r"""
Rijndael-GF

Rijndael-GF is an algebraic implementation of the AES cipher which seeks to
provide a fully generalized algebraic representation of both the whole AES
cipher as well as its individual components.

This class is an algebraic implementation of the Rijndael-GF extension of the
AES cipher, as described in [DR2002]_. The AES cipher itself is defined to
operate on a state in `(\GF{2})^{8 n_t}` where
`n_t \in \{16, 20, 24, 28, 32\}`. Rijndael-GF is a generalization of AES which
allows for operations in `(\GF{2^8})^{n_t}`, enabling more algebraically
sophisticated study of AES and its variants. This implementation of
Rijndael-GF is suitable for learning purposes, for comparison to other
algebraic ciphers, and for studying various techniques of algebraic
cryptanalysis of AES. This cipher is different from
:mod:`Mini-AES <sage.crypto.block_cipher.miniaes>`, which is a
teaching tool for beginners to understand the basic structure of AES.

An algebraic implementation of Rijndael-GF is achieved by recognizing that
for each round component function `\phi` of AES (SubBytes, ShiftRows, etc.)
operating on state matrices, every entry of the output matrix `B = \phi(A)` is
representable as a polynomial with variables being the entries of the input
state matrix `A`. Correspondingly, this implementation of Rijndael-GF provides
a ``RijndaelGF.Round_Component_Poly_Constr`` class which allows for creation
of these such polynomials. For each round component function `\phi` of
Rijndael-GF there exists a ``Round_Component_Poly_Constr`` object with a
``__call__`` method of the form ``__call__(i, j)`` which returns a polynomial
representing `\phi(A)_{i,j}` in terms of the entries of `A`.
There additionally are various methods provided which allow for easy polynomial
evaluation and for simple creation of ``Round_Component_Poly_Constr`` objects
representing more complex aspects of the cipher.

This approach to implementing Rijndael-GF bears some similarity to the
multivariate quadratic (MQ) systems utilized in :mod:`SR <sage.crypto.mq.sr>`,
in that the MQ systems also seek to describe the AES cipher as a system of
algebraic equations. Despite this initial similarity though, Rijndael-GF and
:mod:`SR <sage.crypto.mq.sr>` are quite different as this implementation
seeks to provide a fully generalized algebraic representation of both the
whole AES cipher as well as its individual components, while
:mod:`SR <sage.crypto.mq.sr>` is instead a family of parameterizable variants
of the AES suitable as a framework for comparing different cryptanalytic
techniques that can be brought to bear on the AES.

AUTHORS:

- Thomas Gagne (2015-06): initial version

EXAMPLES

We build Rijndael-GF with a block length of 4 and a key length of 6::

    sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
    sage: rgf = RijndaelGF(4, 6)

We can encrypt plaintexts and decrypt and ciphertexts by calling the
``encrypt`` and ``decrypt`` methods or by calling the Rijndael-GF object
explicitly. Note that the default input format is a hex string. ::

    sage: plaintext = '00112233445566778899aabbccddeeff'
    sage: key = '000102030405060708090a0b0c0d0e0f1011121314151617'
    sage: rgf.encrypt(plaintext, key)
    'dda97ca4864cdfe06eaf70a0ec0d7191'
    sage: rgf.decrypt('dda97ca4864cdfe06eaf70a0ec0d7191', key)
    '00112233445566778899aabbccddeeff'

We can also use binary strings as input and output. ::

    sage: plain = '11101011100111110000000111001100' * 4
    sage: key = '01100010111101101000110010111010' * 6
    sage: ciphertext = rgf(plain, key, format='binary')
    sage: ciphertext
    '11010011000010011010110001000011101110110100110100110010011011111100011011100111110011100111010011001110110100011100000011111011'
    sage: rgf(ciphertext, key, algorithm='decrypt', format='binary') == plain
    True

[DR2002]_ demonstrates an example of encryption which takes the plaintext
'3243f6a8885a308d313198a2e0370734' and the key
'2b7e151628aed2a6abf7158809cf4f3c' and returns the ciphertext
'3902dc1925dc116a8409850b1dfb9732'. We can use this example to demonstrate
the correctness of this implementation::

    sage: rgf = RijndaelGF(4, 4) # change dimensions for this example
    sage: plain = '3243f6a8885a308d313198a2e0370734'
    sage: key = '2b7e151628aed2a6abf7158809cf4f3c'
    sage: expected_ciphertext = '3925841d02dc09fbdc118597196a0b32'
    sage: rgf.encrypt(plain, key) == expected_ciphertext
    True

::

    sage: rgf = RijndaelGF(4, 6) # revert to previous dimensions

To build polynomials representing entries of the output matrix `B = \phi(A)`
for any round component function `\phi`, each of the round component functions
(SubBytes, ShiftRows, and MixColumns) have a ``Round_Component_Poly_Constr``
object associated with it for building polynomials. These objects can be
accessed by calling their getter functions: ``rgf.sub_bytes_poly()``,
``rgf.shift_rows_poly()``, and ``rgf.mix_columns_poly()``. Each returned
object has a ``__call__`` method which takes an index ``i,j`` and an
``algorithm`` flag ('encrypt' or 'decrypt') and returns a polynomial
representing `\phi(A)_{i,j}` in terms of the entries of `A`, where `A` is an
arbitrary state matrix and `\phi` is the round component function associated
with that particular ``Round_Component_Poly_Constr`` object. Some of these
objects' ``__call__`` methods also have additional keywords to modify their
behavior, and so we describe the usage of each object below.

``rgf.shift_rows_poly()`` and ``rgf.mix_columns_poly()`` do not have any
additional keywords for their ``__call__`` methods and we can call them as
such::

    sage: sr_pc = rgf.shift_rows_poly_constr()
    sage: sr_pc(1, 2)
    a13
    sage: sr_pc(2, 3, algorithm='decrypt')
    a21

::

    sage: mc_pc = rgf.mix_columns_poly_constr()
    sage: mc_pc(1, 2)
    a02 + (x)*a12 + (x + 1)*a22 + a32
    sage: mc_pc(2, 3, algorithm='decrypt')
    (x^3 + x^2 + 1)*a03 + (x^3 + 1)*a13 + (x^3 + x^2 + x)*a23 + (x^3 + x + 1)*a33

``rgf.sub_bytes_poly()`` has a single keyword ``no_inversion=False``, which
when set to ``True`` returns only the affine transformation step of SubBytes.
Below describes the usage of ``rgf.sub_bytes_poly()`` ::

    sage: sb_pc = rgf.sub_bytes_poly_constr()
    sage: sb_pc(1, 2)
    (x^2 + 1)*a12^254 +
    (x^3 + 1)*a12^253 +
    (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a12^251 +
    (x^5 + x^2 + 1)*a12^247 +
    (x^7 + x^6 + x^5 + x^4 + x^2)*a12^239 +
    a12^223 +
    (x^7 + x^5 + x^4 + x^2 + 1)*a12^191 +
    (x^7 + x^3 + x^2 + x + 1)*a12^127 +
    (x^6 + x^5 + x + 1)
    sage: sb_pc(2, 3, no_inversion=True)
    (x^7 + x^3 + x^2 + x + 1)*a23^128 +
    (x^7 + x^5 + x^4 + x^2 + 1)*a23^64 +
    a23^32 +
    (x^7 + x^6 + x^5 + x^4 + x^2)*a23^16 +
    (x^5 + x^2 + 1)*a23^8 +
    (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a23^4 +
    (x^3 + 1)*a23^2 +
    (x^2 + 1)*a23 +
    (x^6 + x^5 + x + 1)

Because of the order of the affine transformation and the inversion step in
SubBytes, calling ``rgf.sub_bytes_poly()(i, j, algorithm='decrypt')`` results
in a polynomial with thousands of terms which takes a very long time to
compute. Hence, when using the decryption version of ``rgf.sub_bytes_poly()``
with the intention of evaluating the polynomials it constructs, it is
recommended to first call ``rgf.sub_bytes_poly()(i, j, algorithm='decrypt',
no_inversion=True)`` to get a polynomial representing only the inverse affine
transformation, evaluate this polynomial for a particular input block, then
finally perform the inversion step after the affine transformation polynomial
has been evaluated. ::

    sage: inv_affine = sb_pc(1, 2, algorithm='decrypt',
    ....: no_inversion=True)
    sage: state = rgf._hex_to_GF('ff87968431d86a51645151fa773ad009')
    sage: evaluated = inv_affine(state.list())
    sage: result = evaluated * -1
    sage: rgf._GF_to_hex(result)
    '79'

We can see how the variables of these polynomials are organized in `A`::

    sage: rgf.state_vrs
    [a00 a01 a02 a03]
    [a10 a11 a12 a13]
    [a20 a21 a22 a23]
    [a30 a31 a32 a33]

The final ``Round_Component_Poly_Constr`` object we have not discussed yet is
``add_round_key_poly``, which corresponds to the AddRoundKey round component
function. This object differs from the other ``Round_Component_Poly_Constr``
objects in that it returns polynomials with variables being entries of an
input state `A` as well as entries of various subkeys. Since there are `N_r`
subkeys to choose from, ``add_round_key_poly`` has a keyword of ``round=0`` to
select which subkey to use variables from. ::

    sage: ark_pc = rgf.add_round_key_poly_constr()
    sage: ark_pc(1, 2)
    a12 + k012
    sage: ark_pc(1, 2, algorithm='decrypt')
    a12 + k012
    sage: ark_pc(2, 3, round=7)
    a23 + k723

We can see how key variables are organized in the original key (the key used
to build the rest of the subkeys) below. Note that because key variables are
subkey entries, if the key length is longer than the block length we will have
entries from multiple subkeys in the original key matrix. ::

    sage: rgf.key_vrs
    [k000 k001 k002 k003 k100 k101]
    [k010 k011 k012 k013 k110 k111]
    [k020 k021 k022 k023 k120 k121]
    [k030 k031 k032 k033 k130 k131]

We can evaluate any of these constructed polynomials for a particular input
state (in essence, calculate `\phi(A)_{i,j}`) as such::

    sage: rgf = RijndaelGF(4, 6)
    sage: state = rgf._hex_to_GF('fe7b5170fe7c8e93477f7e4bf6b98071')
    sage: poly = mc_pc(3, 2, algorithm='decrypt')
    sage: poly(state.list())
    x^7 + x^6 + x^5 + x^2 + x

We can use the ``apply_poly`` method to build a matrix whose `i,j` th
entry equals the polynomial ``phi_poly(i, j)`` evaluated for a particular input
state, where ``phi_poly`` is the ``Round_Component_Poly_Constr`` object
associated with the round component function `\phi`. Essentially,
``apply_poly`` calculates `\phi(A)`, where `A` is our input state.
Calling ``apply_poly`` is equivalent to applying the round component function
associated this ``Round_Component_Poly_Constr`` object to `A`. ::

    sage: state = rgf._hex_to_GF('c4cedcabe694694e4b23bfdd6fb522fa')
    sage: result = rgf.apply_poly(state, rgf.sub_bytes_poly_constr())
    sage: rgf._GF_to_hex(result)
    '1c8b86628e22f92fb32608c1a8d5932d'
    sage: result == rgf.sub_bytes(state)
    True

Alternatively, we can pass a matrix of polynomials as input to ``apply_poly``,
which will then return another matrix of polynomials. For example,
``rgf.state_vrs`` can be used as input to make each ``i,j`` th entry of the
output matrix equal ``phi_poly_constr(i, j)``, where ``phi_poly_constr`` is
our inputted ``Round_Component_Poly_Constr`` object. This matrix can then be
passed through again and so on, demonstrating how one could potentially build
a matrix of polynomials representing the entire cipher. ::

    sage: state = rgf.apply_poly(rgf.state_vrs, rgf.shift_rows_poly_constr())
    sage: state
    [a00 a01 a02 a03]
    [a11 a12 a13 a10]
    [a22 a23 a20 a21]
    [a33 a30 a31 a32]
    sage: rgf.apply_poly(state, rgf.add_round_key_poly_constr())
    [a00 + k000 a01 + k001 a02 + k002 a03 + k003]
    [a11 + k010 a12 + k011 a13 + k012 a10 + k013]
    [a22 + k020 a23 + k021 a20 + k022 a21 + k023]
    [a33 + k030 a30 + k031 a31 + k032 a32 + k033]

For any of these ``Round_Component_Poly_Constr`` objects, we can change the
keywords of its ``__call__`` method when ``apply_poly`` invokes it by passing
``apply_poly`` a dictionary mapping keywords to their values. ::

    sage: rgf.apply_poly(rgf.state_vrs, rgf.add_round_key_poly_constr(),
    ....: poly_constr_attr={'round' : 5})
    [a00 + k500 a01 + k501 a02 + k502 a03 + k503]
    [a10 + k510 a11 + k511 a12 + k512 a13 + k513]
    [a20 + k520 a21 + k521 a22 + k522 a23 + k523]
    [a30 + k530 a31 + k531 a32 + k532 a33 + k533]

We can build our own ``Round_Component_Poly_Constr`` objects which correspond
to the composition of multiple round component functions with the ``compose``
method. To do this, if we pass two ``Round_Component_Poly_Constr`` objects
to ``compose`` where the first object corresponds to the round component
function `f` and the second to the round component function `g`, ``compose``
will return a new ``Round_Component_Poly_Constr`` object corresponding to the
function `g \circ f`. This returned ``Round_Component_Poly_Constr`` object
will have the arguments of ``__call__(row, col, algorithm='encrypt')`` and
when passed an index ``i,j`` will return `g(f(A))_{i,j}` in terms of the
entries of `A`. ::

    sage: rcpc = rgf.compose(rgf.shift_rows_poly_constr(),
    ....: rgf.mix_columns_poly_constr())
    sage: rcpc
    A polynomial constructor of a round component of Rijndael-GF block cipher with block length 4, key length 6, and 12 rounds.
    sage: rcpc(2, 1)
    a01 + a12 + (x)*a23 + (x + 1)*a30
    <BLANKLINE>
    sage: state = rgf._hex_to_GF('afb73eeb1cd1b85162280f27fb20d585')
    sage: result = rgf.apply_poly(state, rcpc)
    sage: new_state = rgf.shift_rows(state)
    sage: new_state = rgf.mix_columns(new_state)
    sage: result == new_state
    True
    <BLANKLINE>
    sage: rcpc = rgf.compose(rgf.mix_columns_poly_constr(),
    ....: rgf.shift_rows_poly_constr())
    sage: result = rgf.apply_poly(state, rcpc, algorithm='decrypt')
    sage: new_state = rgf.mix_columns(state, algorithm='decrypt')
    sage: new_state = rgf.shift_rows(new_state, algorithm='decrypt')
    sage: new_state == result
    True

Alternatively, we can use ``compose`` to build the polynomial output of
a ``Round_Component_Poly_Constr`` object corresponding to the composition of
multiple round functions like above without having to explicitly build our
own ``Round_Component_Poly_Constr`` object. To do this, we simply make the
first input a ``Round_Component_Poly_Constr`` object corresponding to a
round component function `f` and make the second input a polynomial
representing `g(A)_{i,j}` for a round component function `g`. Given this,
``compose`` will return a polynomial representing `g(f(A))_{i,j}` in terms
of the entries of `A`. ::

    sage: poly = rgf.mix_columns_poly_constr()(0, 3)
    sage: poly
    (x)*a03 + (x + 1)*a13 + a23 + a33
    sage: rgf.compose(rgf.sub_bytes_poly_constr(), poly)
    (x^3 + x)*a03^254 +
    (x^3 + x^2 + x + 1)*a13^254 +
    (x^2 + 1)*a23^254 +
    (x^2 + 1)*a33^254 +
    (x^4 + x)*a03^253 +
    (x^4 + x^3 + x + 1)*a13^253 +
    (x^3 + 1)*a23^253 +
    (x^3 + 1)*a33^253 +
    (x^7 + x^6 + x^5 + x^3 + 1)*a03^251 +
    (x^4)*a13^251 +
    (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a23^251 +
    (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a33^251 +
    (x^6 + x^3 + x)*a03^247 +
    (x^6 + x^5 + x^3 + x^2 + x + 1)*a13^247 +
    (x^5 + x^2 + 1)*a23^247 +
    (x^5 + x^2 + 1)*a33^247 +
    (x^7 + x^6 + x^5 + x^4 + x + 1)*a03^239 +
    (x^2 + x + 1)*a13^239 +
    (x^7 + x^6 + x^5 + x^4 + x^2)*a23^239 +
    (x^7 + x^6 + x^5 + x^4 + x^2)*a33^239 +
    (x)*a03^223 +
    (x + 1)*a13^223 +
    a23^223 +
    a33^223 +
    (x^6 + x^5 + x^4 + 1)*a03^191 +
    (x^7 + x^6 + x^2)*a13^191 +
    (x^7 + x^5 + x^4 + x^2 + 1)*a23^191 +
    (x^7 + x^5 + x^4 + x^2 + 1)*a33^191 +
    (x^2 + 1)*a03^127 +
    (x^7 + x^3 + x)*a13^127 +
    (x^7 + x^3 + x^2 + x + 1)*a23^127 +
    (x^7 + x^3 + x^2 + x + 1)*a33^127 +
    (x^6 + x^5 + x + 1)

If we use ``algorithm='decrypt'`` as an argument to ``compose``, then the
value of ``algorithm`` will be passed directly to the first argument of
``compose`` (a ``Round_Component_Poly_Constr`` object) when it is called,
provided the second argument is a polynomial. Setting this flag does nothing
if both arguments are ``Round_Component_Poly_Constr`` objects, since the
returned ``Round_Component_Poly_Constr`` object's ``__call__`` method must have
its own ``algorithm`` keyword defaulted to 'encrypt'. ::

    sage: poly = rgf.shift_rows_poly_constr()(2, 1)
    sage: rgf.compose(rgf.mix_columns_poly_constr(), poly, algorithm='decrypt')
    (x^3 + x^2 + 1)*a03 + (x^3 + 1)*a13 + (x^3 + x^2 + x)*a23 + (x^3 + x + 1)*a33
    <BLANKLINE>
    sage: state = rgf._hex_to_GF('80121e0776fd1d8a8d8c31bc965d1fee')
    sage: with_decrypt = rgf.compose(rgf.sub_bytes_poly_constr(),
    ....: rgf.shift_rows_poly_constr(), algorithm='decrypt')
    sage: result_wd = rgf.apply_poly(state, with_decrypt)
    sage: no_decrypt = rgf.compose(rgf.sub_bytes_poly_constr(),
    ....: rgf.shift_rows_poly_constr())
    sage: result_nd = rgf.apply_poly(state, no_decrypt)
    sage: result_wd == result_nd
    True

We can also pass keyword dictionaries of ``f_attr`` and ``g_attr`` to
``compose`` to make ``f`` and ``g`` use those keywords during polynomial
creation. ::

    sage: rcpc = rgf.compose(rgf.add_round_key_poly_constr(),
    ....: rgf.add_round_key_poly_constr(),
    ....: f_attr={'round' : 4}, g_attr={'round' : 7})
    sage: rcpc(1, 2)
    a12 + k412 + k712

In addition to building polynomial representations of state matrices, we can
also build polynomial representations of elements of the expanded key with the
``expand_key_poly`` method. However, since the key schedule is defined
recursively, it is impossible to build polynomials for the key schedule in
the same manner as we do for the round component functions. Consequently,
``expand_round_key_poly()`` is not a ``Round_Component_Poly_Constr`` object.
Instead, ``expand_key_poly`` is a method which takes an index ``i,j`` and a
round number ``round``, and returns a polynomial representing the `i,j` th
entry of the ``round`` th round key. This polynomial's variables are entries
of the original key we built above. ::

    sage: rgf.expand_key_poly(1, 2, 0)
    k012
    sage: rgf.expand_key_poly(1, 1, 1)
    k111
    sage: rgf.expand_key_poly(1, 2, 1)
    (x^2 + 1)*k121^254 +
    (x^3 + 1)*k121^253 +
    (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*k121^251 +
    (x^5 + x^2 + 1)*k121^247 +
    (x^7 + x^6 + x^5 + x^4 + x^2)*k121^239 +
    k121^223 +
    (x^7 + x^5 + x^4 + x^2 + 1)*k121^191 +
    (x^7 + x^3 + x^2 + x + 1)*k121^127 +
    k010 +
    (x^6 + x^5 + x)

Since ``expand_key_poly`` is not actually a
``Round_Component_Poly_Constr`` object, we cannot use it as input to
``apply_poly`` or ``compose``. ::

    sage: rgf.apply_poly(state, rgf.expand_key_poly)
    Traceback (most recent call last):
    ...
    TypeError: keyword 'poly_constr' must be a Round_Component_Poly_Constr
    sage: rgf.compose(rgf.expand_key_poly, rgf.sub_bytes_poly_constr())
    Traceback (most recent call last):
    ...
    TypeError: keyword 'f' must be a Round_Component_Poly_Constr
"""

#*****************************************************************************
#       Copyright (C) 2015 Thomas Gagne <thomasgagne100@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#                  http://www.gnu.org/licenses/
#*****************************************************************************
from __future__ import print_function, division
from six import string_types

from sage.matrix.constructor import matrix
from sage.matrix.constructor import column_matrix
from sage.structure.element import Matrix
from sage.rings.finite_rings.finite_field_constructor import FiniteField
from sage.rings.integer import Integer
from sage.structure.sage_object import SageObject
from sage.matrix.matrix_space import MatrixSpace
from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing

class RijndaelGF(SageObject):

    def __init__(self, Nb, Nk, state_chr='a', key_chr='k'):
        r"""
        An algebraically generalized version of the AES cipher.

        INPUT:

        - ``Nb`` -- The block length of this instantiation. Must be between 4
          and 8.

        - ``Nk`` -- The key length of this instantiation. Must be between 4 and 8.

        - ``state_chr`` -- The variable name for polynomials representing
          elements from state matrices.

        - ``key_chr`` -- The variable name for polynomials representing
          elements of the key schedule.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(6, 8)
            sage: rgf
            Rijndael-GF block cipher with block length 6, key length 8, and 14 rounds.

        By changing ``state_chr`` we can alter the names of variables in
        polynomials representing elements from state matrices. ::

            sage: rgf = RijndaelGF(4, 6, state_chr='myChr')
            sage: rgf.mix_columns_poly_constr()(3, 2)
            (x + 1)*myChr02 + myChr12 + myChr22 + (x)*myChr32

        We can also alter the name of variables in polynomials representing
        elements from round keys by changing ``key_chr``. ::

            sage: rgf = RijndaelGF(4, 6, key_chr='myKeyChr')
            sage: rgf.expand_key_poly(1, 2, 1)
            (x^2 + 1)*myKeyChr121^254 +
            (x^3 + 1)*myKeyChr121^253 +
            (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*myKeyChr121^251 +
            (x^5 + x^2 + 1)*myKeyChr121^247 +
            (x^7 + x^6 + x^5 + x^4 + x^2)*myKeyChr121^239 +
            myKeyChr121^223 +
            (x^7 + x^5 + x^4 + x^2 + 1)*myKeyChr121^191 +
            (x^7 + x^3 + x^2 + x + 1)*myKeyChr121^127 +
            myKeyChr010 +
            (x^6 + x^5 + x)
        """
        if Nb not in range(4, 9):
            msg = "Block length Nb must be in the range 4 - 8, not {0}"
            raise ValueError(msg.format(Nb))
        if Nk not in range(4, 9):
            msg = "Key length Nk must be in the range 4 - 8, not {0}"
            raise ValueError(msg.format(Nk))
        if not isinstance(state_chr, string_types):
            msg = "state_chr must be a string, not {0}"
            raise TypeError(msg.format(state_chr))
        if not isinstance(key_chr, string_types):
            msg = "key_chr must be a string, not {0}"
            raise TypeError(msg.format(key_chr))

        self._Nb = Nb
        self._Nk = Nk
        round_num_table = matrix([[10,11,12,13,14], [11,11,12,13,14],
                                  [12,12,12,13,14], [13,13,13,13,14],
                                  [14,14,14,14,14]])
        self._Nr = round_num_table[self._Nb - 4, self._Nk - 4]
        from sage.rings.polynomial.polynomial_ring import polygen

        # Build framework for polynomial creation.
        from sage.rings.finite_rings.integer_mod_ring import Integers
        pgen = polygen(Integers(2))
        mod = pgen**8 + pgen**4 + pgen**3 + pgen + 1
        self._F = FiniteField(2**8, 'x', modulus=mod)
        state_names = [state_chr + str(i) + str(j)
                       for i in range(4) for j in range(self._Nb)]
        subkey_names = [key_chr + str(r) + str(i) + str(j)
                        for r in range(self._Nr + 1) for i in range(4)
                        for j in range(self._Nb)]
        self._state_PR = PolynomialRing(self._F, len(state_names), state_names)
        self._all_PR = PolynomialRing(self._F, len(state_names + subkey_names),
                                      state_names + subkey_names)
        self.state_vrs = matrix(4, self._Nb, self._state_PR.gens())
        self.subkey_vrs_list = list(self._all_PR.gens()[4 * self._Nb:])
        self.subkey_vrs = [matrix(4, self._Nb,
                           self.subkey_vrs_list[(4 * self._Nb)*i :
                                        (4 * self._Nb)*(i+1)])
                           for i in range(self._Nr)]
        self.key_vrs = column_matrix([
                       self.subkey_vrs[int(i / self._Nb)].column(i % 4)
                       for i in range(self._Nk)])
        self._shiftrows_offsets_E = matrix([[0,1,2,3], [0,1,2,3], [0,1,2,3],
                                   [0,1,2,4], [0,1,3,4]])
        self._shiftrows_offsets_D = matrix([[0,-1,-2,-3], [0,-1,-2,-3],
                                           [0,-1,-2,-3], [0,-1,-2,-4],
                                           [0,-1,-3,-4]])
        self._sb_E_coeffs = [self._F("x^2 + 1"),
                             self._F("x^3 + 1"),
                             self._F("x^7 + x^6 + x^5 + x^4 + x^3 + 1"),
                             self._F("x^5 + x^2 + 1"),
                             self._F("x^7 + x^6 + x^5 + x^4 + x^2"),
                             self._F("1"),
                             self._F("x^7 + x^5 + x^4 + x^2 + 1"),
                             self._F("x^7 + x^3 + x^2 + x + 1")]
        self._sb_D_coeffs = [self._F("x^2 + 1"),
                             self._F("x^7 + x^6 + x^5 + x^4 + x^3 + x^2 + x"),
                             self._F("x^6 + x^5 + x^4 + x^3 + x^2 + x + 1"),
                             self._F("x^6 + x^4 + x^3 + x"),
                             self._F("x^6 + x^5 + x^4 + x^3"),
                             self._F("x^6 + x^4 + x^3 + 1"),
                             self._F("x^7 + x^6 + x^4 + x^3 + x + 1"),
                             self._F("x^6 + x^5 + x^3 + x^2 + x")]
        mixcols_E_row = [self._F('x'), self._F('x+1'), self._F('1'),
                         self._F('1')]
        self._mixcols_E = matrix([mixcols_E_row[-i:] + mixcols_E_row[:-i]
                                  for i in range(4)])
        mixcols_D_row = [self._F('x^3 + x^2 + x'), self._F('x^3 + x + 1'),
                         self._F('x^3 + x^2 + 1'), self._F('x^3 + 1')]
        self._mixcols_D = matrix([mixcols_D_row[-i:] + mixcols_D_row[:-i]
                                  for i in range(4)])
        # Build the Round_Component_Poly_Constr objects
        self._add_round_key_rcpc = \
        RijndaelGF.Round_Component_Poly_Constr(self._add_round_key_pc, self,
                                               "Add Round Key")
        self._sub_bytes_rcpc = \
        RijndaelGF.Round_Component_Poly_Constr(self._sub_bytes_pc, self,
                                               "SubBytes")
        self._mix_columns_rcpc = \
        RijndaelGF.Round_Component_Poly_Constr(self._mix_columns_pc, self,
                                               "Mix Columns")
        self._shift_rows_rcpc = \
        RijndaelGF.Round_Component_Poly_Constr(self._shift_rows_pc, self,
                                               "Shift Rows")

    def __call__(self, text, key, algorithm='encrypt', format='hex'):
        r"""
        Returns the encryption/decryption of ``text`` with key ``key``.

        INPUT:

        - ``text`` -- A plaintext to encrypt or a ciphertext to decrypt.

        - ``key`` -- The key to encrypt/decrypt ``text`` with.

        - ``algorithm`` -- Whether to encrypt or decrypt ``text``. Flag for
          encryption is "encrypt", flag for decryption is "decrypt".

        - ``format`` -- The format of ``text`` and ``key``, either "hex" or
          "binary"

        OUTPUT:

        - The encrypted or decrypted message ``text`` with key ``key``.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: text = 'ef053f7c8b3d32fd4d2a64ad3c93071a'
            sage: key = '2d7e86a339d9393ee6570a1101904e16'
            sage: rgf(text, key)
            '84e75b142c8fd5a445312c0a9b2d6699'
            sage: rgf(text, key, algorithm='decrypt')
            '9bf83275406304f050c826ca72d035e6'

        We can also use binary strings for ``text`` and ``key``. ::

            sage: text = '11011100011010000011101111011011' * 4
            sage: key = '01000000000011000101101011011110' * 4
            sage: rgf(text, key, format='binary')
            '00011000010110010011100100010111010101001000010010100110101010101111001001100000011111011100100011010001010100110011000111110011'
            sage: rgf(text, key, algorithm='decrypt', format='binary')
            '11000110011001001110000101011101001001010101110001110010000111110000010111111101000011010101101011111100100001010010111000011010'
        """

        if algorithm == 'encrypt':
            return self.encrypt(text, key, format)
        elif algorithm == 'decrypt':
            return self.decrypt(text, key, format)
        else:
            raise ValueError(("keyword 'algorithm' must be either 'encrypt' "
                             "or 'decrypt'"))

    def __repr__(self):
        r"""
        Returns the string representation of ``self``.

        EXAMPLES ::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(5, 8)
            sage: rgf
            Rijndael-GF block cipher with block length 5, key length 8, and 14 rounds.
        """

        msg = ("Rijndael-GF block cipher with block length {0}, key length "
               "{1}, and {2} rounds.")
        return msg.format(self._Nb, self._Nk, self._Nr)

    def block_length(self):
        r"""
        Returns the block length of this instantiation of Rijndael-GF.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 6)
            sage: rgf.block_length()
            4
        """
        return self._Nb

    def key_length(self):
        r"""
        Returns the key length of this instantiation of Rijndael-GF.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 8)
            sage: rgf.key_length()
            8
        """
        return self._Nk

    def number_rounds(self):
        r"""
        Returns the number of rounds used in this instantiation of Rijndael-GF.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(5, 4)
            sage: rgf.number_rounds()
            11
        """
        return self._Nr

    def _hex_to_GF(self, H, matrix=True):
        r"""
        Returns a matrix/list of elements of `\GF{2^8}` corresponding to ``H``.

        INPUT:

        - ``H`` -- A hex string where every two hex characters correspond to a
          single element in `\GF{2^8}`

        - ``matrix`` -- (default: ``True``) Returns a list if ``False``;
          returns a state matrix if ``True``.

        OUTPUT:

        - A list of or a state matrix of elements of `\GF{2^8}` where each
          element corresponds to the appropriate hex value in ``H``. In
          particular, every element `a_7x^7 + a_6x^6 + a_5x^5 + a_4x^4 +
          a_3x^3 + a_2x^2 + a_1x^1 + a_0` in `\GF{2^8}` corresponds to the
          8-bit binary string '`a_7a_6a_5a_4a_3a_2a_1a_0`'.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: state = rgf._hex_to_GF('1147659047cf663b9b0ece8dfc0bf1f0')
            sage: output = rgf.shift_rows(state)
            sage: rgf._GF_to_hex(output)
            '11cfcef0470ef1909b0b653bfc47668d'

        We can output a list instead by setting ``matrix`` to ``False``. ::

            sage: rgf._hex_to_GF('2f', matrix=False)
            [x^5 + x^3 + x^2 + x + 1]
            sage: rgf._hex_to_GF('1a2b0f', matrix=False)
            [x^4 + x^3 + x, x^5 + x^3 + x + 1, x^3 + x^2 + x + 1]
        """
        if not isinstance(H, string_types) or \
           any(c not in '0123456789abcdefABCDEF' for c in H):
            raise TypeError("keyword 'H' must be a hex string")

        def hx_to_gf(h):
            return self._F(map(int, bin(int(h, 16))[2:].zfill(8))[::-1])
        hexes = [H[2 * i] + H[2 * i + 1] for i in range(len(H) // 2)]
        result = [hx_to_gf(h) for h in hexes]
        if matrix:
            return column_matrix(len(result) // 4, 4, result)
        else:
            return result

    def _GF_to_hex(self, GF):
        r"""
        Returns the hex string representation of ``GF``.

        INPUT:

        - ``GF`` -- Either a state matrix over `\GF{2^8}`, a list of elements
          from `\GF{2^8}`, or a single element from `\GF{2^8}`

        OUTPUT:

        - A hex string representation of ``GF``, where every two characters in
          the string correspond to a single element in `\GF{2^8}`. In
          particular, every element `a_7x^7 + a_6x^6 + a_5x^5 + a_4x^4 +
          a_3x^3 + a_2x^2 + a_1x^1 + a_0` in `\GF{2^8}` corresponds to the
          8-bit binary string '`a_7a_6a_5a_4a_3a_2a_1a_0`'.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4,4)
            sage: F.<a> = GF(2^8)
            sage: els = [a^7 + a^5 + a + 1, a^7 + a^6 + a^4 + a^2]
            sage: rgf._GF_to_hex(els)
            'a3d4'
            <BLANKLINE>
            sage: h = '8fb999c973b26839c7f9d89d85c68c72'
            sage: h == rgf._GF_to_hex(rgf._hex_to_GF(h))
            True

        We can use this to get concise output from round functions. ::

            sage: plain = rgf._hex_to_GF('72b86c7c0f0d52d3e0d0da104055036b')
            sage: key = rgf._hex_to_GF('93faa123c2903f4743e4dd83431692de')
            sage: output = rgf.add_round_key(plain, key)
            sage: rgf._GF_to_hex(output)
            'e142cd5fcd9d6d94a3340793034391b5'
        """
        from sage.rings.finite_rings.element_base import is_FiniteFieldElement
        if not isinstance(GF, Matrix) and \
           not isinstance(GF, list) and \
           not is_FiniteFieldElement(GF):
            msg = ("keyword 'GF' must be a matrix over {0}, a list of "
                   "elements from {0}, or a single element from {0}")
            raise TypeError(msg.format(self._F))

        if isinstance(GF, Matrix):
            if not GF.base_ring().is_field() or \
               not GF.base_ring().is_finite() or \
               not GF.base_ring().order() == 2**8:
                msg = "The elements of keyword 'GF' must all be from {0}"
                raise TypeError(msg.format(self._F))
            return ''.join([self._GF_to_hex(el)
                            for col in GF.columns() for el in col])
        elif isinstance(GF, list):
            if not all([g.parent().is_field() and g.parent().is_finite() and
                        g.parent().order() == 2**8 for g in GF]):
                msg = "The elements of keyword 'GF' must all be from {0}"
                raise TypeError(msg.format(self._F))
            return ''.join([self._GF_to_hex(el) for el in GF])
        else:
            if not GF.parent().is_field() or \
               not GF.parent().is_finite() or \
               not GF.parent().order() == 2**8:
                msg = "keyword 'GF' must be in"
                raise TypeError(msg.format(self._F))
            return hex(GF.integer_representation())[2:].zfill(2)

    def _bin_to_GF(self, B, matrix=True):
        r"""
        Returns a matrix/list of elements of `\GF{2^8}` corresponding to ``B``.

        INPUT:

        - ``B`` -- A binary string where every eight bits correspond to a
          single element in `\GF{2^8}`

        - ``matrix`` -- (default: ``True``) Returns a list if ``False``.
          Returns a state matrix over `\GF{2^8}` if ``True``.

        OUTPUT:

        - A list of or a state matrix of elements of `\GF{2^8}` where each
          element corresponds to the appropriate 8-bit binary string in ``B``.
          In particular, every element `a_7x^7 + a_6x^6 + a_5x^5 + a_4x^4 +
          a_3x^3 + a_2x^2 + a_1x^1 + a_0` in `\GF{2^8}` corresponds to the
          8-bit binary string '`a_7a_6a_5a_4a_3a_2a_1a_0`'.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: bs = '11101011100111110000000111001100' * 4
            sage: len(bs)
            128
            sage: state = rgf._bin_to_GF(bs)
            sage: output = rgf.sub_bytes(state)
            sage: rgf._GF_to_bin(output)
            '11101001110110110111110001001011111010011101101101111100010010111110100111011011011111000100101111101001110110110111110001001011'

        We can make this method output a list by setting ``matrix`` to
        ``False``. ::

            sage: bs = '01010011'
            sage: rgf._bin_to_GF(bs, matrix=False)
            [x^6 + x^4 + x + 1]
            sage: bs = '000100000111001000110101110001101101011100110101'
            sage: rgf._bin_to_GF(bs, matrix=False)
            [x^4,
             x^6 + x^5 + x^4 + x,
             x^5 + x^4 + x^2 + 1,
             x^7 + x^6 + x^2 + x,
             x^7 + x^6 + x^4 + x^2 + x + 1,
             x^5 + x^4 + x^2 + 1]
        """
        if not isinstance(B, string_types) or any(c not in '01' for c in B):
            raise TypeError("keyword 'B' must be a binary string")

        def bn_to_gf(b):
            return self._F(map(int, b)[::-1])
        bins = [B[8 * i : 8 * (i + 1)] for i in range(len(B) // 8)]
        result = [bn_to_gf(b) for b in bins]
        if matrix:
            return column_matrix(len(result) // 4, 4, result)
        else:
            return result

    def _GF_to_bin(self, GF):
        r"""
        Returns the binary string representation of ``GF``.

        INPUT:

        - ``GF`` -- Either a state matrix over `\GF{2^8}`, a list of elements
          from `\GF{2^8}`, or a single element from `\GF{2^8}`

        OUTPUT:

        - A binary string representation of ``GF``, where every eight
          characters in the string corresponds to a single element in
          `\GF{2^8}`. In particular, every element `a_7x^7 + a_6x^6 + a_5x^5 +
          a_4x^4 + a_3x^3 + a_2x^2 + a_1x^1 + a_0` in `\GF{2^8}` corresponds
          to the binary string '`a_7a_6a_5a_4a_3a_2a_1a_0`'.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: F.<a> = GF(2^8)
            sage: els = [a^7 + a^5 + a + 1, a^7 + a^6 + a^4 + a^2]
            sage: rgf._GF_to_bin(els)
            '1010001111010100'

        We can use this to get clearer output from the round functions. ::

            sage: plain = '11101011100111110000000111001100' * 4
            sage: plain_state = rgf._bin_to_GF(plain)
            sage: key = '00110011100000001111100111010111' * 4
            sage: key_state = rgf._bin_to_GF(key)
            sage: output = rgf.add_round_key(plain_state, key_state)
            sage: rgf._GF_to_bin(output)
            '11011000000111111111100000011011110110000001111111111000000110111101100000011111111110000001101111011000000111111111100000011011'
        """
        from sage.rings.finite_rings.element_base import is_FiniteFieldElement
        if not isinstance(GF, Matrix) and \
           not isinstance(GF, list) and \
           not is_FiniteFieldElement(GF):
            msg = ("keyword 'GF' must be a matrix over {0}, a list of "
                   "elements from {0}, or a single element from {0}")
            raise TypeError(msg.format(self))

        if isinstance(GF, Matrix):
            if not GF.base_ring().is_field() or \
               not GF.base_ring().is_finite() or \
               not GF.base_ring().order() == 2**8:
                msg = "The elements of keyword 'GF' must all be from {0}"
                raise TypeError(msg.format(self._F))
            return ''.join([self._GF_to_bin(el)
                            for col in GF.columns() for el in col])
        elif isinstance(GF, list):
            if not all([g.parent().is_field() and g.parent().is_finite() and
                        g.parent().order() == 2**8 for g in GF]):
                msg = "The elements of keyword 'GF' must all be from {0}"
                raise TypeError(msg.format(self._F))
            return ''.join([self._GF_to_bin(el) for el in GF])
        else:
            if not GF.parent().is_field() or \
               not GF.parent().is_finite() or \
               not GF.parent().order() == 2**8:
                msg = "keyword 'GF' must be in"
                raise TypeError(msg.format(self._F))
            return bin(GF.integer_representation())[2:].zfill(8)

    def encrypt(self, plain, key, format='hex'):
        r"""
        Returns the plaintext ``plain`` encrypted with the key ``key``.

        INPUT:

        - ``plain`` -- The plaintext to be encrypted.

        - ``key`` -- The key to encrypt ``plain`` with.

        - ``format`` -- (default: ``hex``) The string format of ``key`` and
          ``plain``, either "hex" or "binary".

        OUTPUT:

        - A string of the plaintext ``plain`` encrypted with the key ``key``.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: key = 'c81677bc9b7ac93b25027992b0261996'
            sage: plain = 'fde3bad205e5d0d73547964ef1fe37f1'
            sage: expected_ciphertext = 'e767290ddfc6414e3c50a444bec081f0'
            sage: rgf.encrypt(plain, key) == expected_ciphertext
            True

        We can encrypt binary strings as well. ::

            sage: key = '10010111110000011111011011010001' * 4
            sage: plain = '00000000101000000000000001111011' * 4
            sage: expected_ciphertext = ('11010111100100001010001011110010111'
            ....: '1110011000000011111100100011011100101000000001000111000010'
            ....: '00100111011011001000111101111110100')
            sage: result = rgf.encrypt(plain, key, format='binary')
            sage: result == expected_ciphertext
            True
        """
        if format == 'hex':
            if not isinstance(plain, string_types) or \
               any(c not in '0123456789abcdefABCDEF' for c in plain):
                raise TypeError("'plain' keyword must be a hex string")
            if len(plain) != 8 * self._Nb:
                msg = "'plain' keyword\'s length must be {0}, not{1}"
                raise ValueError(msg.format(8 * self._Nb, len(plain)))
            if not isinstance(key, string_types) or \
               any(c not in '0123456789abcdefABCDEF' for c in key):
                raise TypeError("'key' keyword must be a hex string")
            if len(key) != 8 * self._Nk:
                msg = "'key' keyword's length must be {0}, not {1}"
                raise ValueError(msg.format(8 * self._Nk, len(key)))
            state = self._hex_to_GF(plain)
            key_state = self._hex_to_GF(key)
            roundKeys = self.expand_key(key_state)
        elif format == 'binary':
            if not isinstance(plain, string_types) or \
               any(c not in '01' for c in plain):
                raise TypeError("'plain' keyword must be a binary string")
            if len(plain) != 32 * self._Nb:
                msg = "'plain' keyword's length must be {0}, not {1}"
                raise ValueError(msg.format(32 * self._Nb, len(plain)))
            if not isinstance(key, string_types) or \
               any(c not in '01' for c in key):
                raise TypeError("'key' keyword must be a binary string")
            if len(key) != 32 * self._Nk:
                msg = "'key' keyword's length must be {0}, not {1}"
                raise ValueError(msg.format(32 * self._Nk, len(key)))
            state = self._bin_to_GF(plain)
            key_state = self._bin_to_GF(key)
            roundKeys = self.expand_key(key_state)
        else:
            raise ValueError(("'format' keyword must be either 'hex' or "
                             "'binary'"))

        state = self.add_round_key(state, roundKeys[0])
        for r in range(self._Nr-1):
            state = self.sub_bytes(state, algorithm='encrypt')
            state = self.shift_rows(state, algorithm='encrypt')
            state = self.mix_columns(state, algorithm='encrypt')
            state = self.add_round_key(state, roundKeys[r+1])
        state = self.sub_bytes(state, algorithm='encrypt')
        state = self.shift_rows(state, algorithm='encrypt')
        state = self.add_round_key(state, roundKeys[self._Nr])

        if format == 'hex':
            return self._GF_to_hex(state)
        else:
            return self._GF_to_bin(state)

    def decrypt(self, ciphertext, key, format='hex'):
        r"""
        Returns the ciphertext ``ciphertext`` decrypted with the key ``key``.

        INPUT:

        - ``ciphertext`` -- The ciphertext to be decrypted.

        - ``key`` -- The key to decrypt ``ciphertext`` with.

        - ``format`` -- (default: ``hex``) The string format that both
          ``ciphertext`` and ``key`` must be in, either "hex" or "binary".

        OUTPUT:

        - A string in the format ``format`` of ``ciphertext`` decrypted with
          key ``key``.

        EXAMPLES ::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: key = '2dfb02343f6d12dd09337ec75b36e3f0'
            sage: ciphertext = '54d990a16ba09ab596bbf40ea111702f'
            sage: expected_plaintext = '1e1d913b7274ad9b5a4ab1a5f9133b93'
            sage: rgf.decrypt(ciphertext, key) == expected_plaintext
            True

        We can also decrypt messages using binary strings. ::

            sage: key = '00011010000011100011000000111101' * 4
            sage: ciphertext = '00110010001110000111110110000001' * 4
            sage: expected_plaintext = ('101111111010011100111100101010100111'
            ....: '1111010000101101100001101000000000000000010000000100111011'
            ....: '0100001111100011010001101101001011')
            sage: result = rgf.decrypt(ciphertext, key, format='binary')
            sage: result == expected_plaintext
            True
        """
        if format == 'hex':
            if not isinstance(ciphertext, string_types) or \
               any(c not in '0123456789abcdefABCDEF' for c in ciphertext):
                raise TypeError("'ciphertext' keyword must be a hex string")
            if len(ciphertext) != 8 * self._Nb:
                msg = "'ciphertext' keyword's length must be {0}, not{1}"
                raise ValueError(msg.format(8 * self._Nb, len(ciphertext)))
            if not isinstance(key, string_types) or \
               any(c not in '0123456789abcdefABCDEF' for c in key):
                raise TypeError("'key' keyword must be a hex string")
            if len(key) != 8 * self._Nk:
                msg = "'key' keyword's length must be {0}, not {1}"
                raise ValueError(msg.format(8 * self._Nk, len(key)))
            state = self._hex_to_GF(ciphertext)
            key_state = self._hex_to_GF(key)
            roundKeys = self.expand_key(key_state)
        elif format == 'binary':
            if not isinstance(ciphertext, string_types) or \
               any(c not in '01' for c in ciphertext):
                raise TypeError(("'ciphertext' keyword must be a binary "
                                 "string"))
            if len(ciphertext) != 32 * self._Nb:
                msg = "'ciphertext' keyword's length must be {0}, not {1}"
                raise ValueError(msg.format(32 * self._Nb, len(ciphertext)))
            if not isinstance(key, string_types) or \
               any(c not in '01' for c in key):
                raise TypeError("'key' keyword must be a binary string")
            if len(key) != 32 * self._Nk:
                msg = "'key' keyword\'s length must be {0}, not {1}"
                raise ValueError(msg.format(32 * self._Nk, len(key)))
            state = self._bin_to_GF(ciphertext)
            key_state = self._bin_to_GF(key)
            roundKeys = self.expand_key(key_state)
        else:
            raise ValueError(("'format' keyword must be either \'hex\' or "
                             "'binary'"))

        state = self.add_round_key(state, roundKeys[self._Nr])
        state = self.shift_rows(state, algorithm='decrypt')
        state = self.sub_bytes(state, algorithm='decrypt')
        for r in range(self._Nr-1):
            state = self.add_round_key(state, roundKeys[self._Nr - r - 1])
            state = self.mix_columns(state, algorithm='decrypt')
            state = self.shift_rows(state, algorithm='decrypt')
            state = self.sub_bytes(state, algorithm='decrypt')
        state = self.add_round_key(state, roundKeys[0])

        if format == 'hex':
            return self._GF_to_hex(state)
        else:
            return self._GF_to_bin(state)

    def _check_valid_PRmatrix(self, PRm, keyword):
        r"""
        Raises an error if ``PRm`` is not a valid input matrix over ``F``.

        INPUT:

        - ``PRm`` -- If ``PRm`` is a `4 \times Nb` matrix with entries from
          the multivariate PolynomialRing ``_all_PR``, this method does nothing
          `\GF{2^8}`, this method does nothing. Otherwise, this method raises
          an error. Note that a matrix of elements from `\GF{2^8}` is regarded
          as a matrix with entries from ``_all_PR`` and will pass this test.

        - ``keyword`` -- The name of the keyword ``PRm`` from where this
          method was called, for the potential error message. For example, if
          called from ``sub_bytes``, ``keyword`` would be "state".

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: good_state = rgf._hex_to_GF('0'*32)
            sage: rgf._check_valid_PRmatrix(good_state, 'state')
            sage: rgf._check_valid_PRmatrix(rgf.state_vrs, 'state')
            sage: rgf._check_valid_PRmatrix(5, 'state')
            Traceback (most recent call last):
            ...
            TypeError: keyword 'state' must be a 4 x 4 matrix with entries from a multivariate PolynomialRing over Finite Field in x of size 2^8
            <BLANKLINE>
            sage: entries = [rgf._F.random_element() for i in range(24)]
            sage: wrong_dimensions = matrix(4, 6, entries)
            sage: rgf._check_valid_PRmatrix(wrong_dimensions, 'state')
            Traceback (most recent call last):
            ...
            TypeError: keyword 'state' must be a 4 x 4 matrix with entries from a multivariate PolynomialRing over Finite Field in x of size 2^8
            <BLANKLINE>
            sage: F.<a> = GF(3^4)
            sage: entries = [F.random_element() for i in range(16)]
            sage: wrong_base = matrix(4, 4, entries)
            sage: rgf._check_valid_PRmatrix(wrong_base, 'state')
            Traceback (most recent call last):
            ...
            TypeError: keyword 'state' must be a 4 x 4 matrix with entries from a multivariate PolynomialRing over Finite Field in x of size 2^8
        """
        from sage.rings.polynomial.multi_polynomial_ring_generic import \
            MPolynomialRing_generic
        msg = ("keyword '{0}' must be a {1} x {2} matrix with entries from a "
               "multivariate PolynomialRing over {3}")
        msg = msg.format(keyword, 4, self._Nb, self._F)
        if (not isinstance(PRm, Matrix) or \
            not (PRm.base_ring().is_field() and \
                PRm.base_ring().is_finite() and \
                PRm.base_ring().order() == 256 and \
                PRm.dimensions() == (4, self._Nb))) and \
           (not isinstance(PRm, Matrix) or \
            not isinstance(PRm.base_ring(), MPolynomialRing_generic) or \
            not (PRm.base_ring().base_ring().is_field() and \
                 PRm.base_ring().base_ring().is_finite() and \
                 PRm.base_ring().base_ring().order() == 256) or \
                not PRm.dimensions() == (4, self._Nb)):
            raise TypeError(msg)

    def expand_key(self, key):
        r"""
        Returns the expanded key schedule from ``key``.

        INPUT:

        - ``key`` -- The key to build a key schedule from. Must be a matrix
          over `\GF{2^8}` of dimensions `4 \times N_k`.

        OUTPUT:

        - A length `Nr` list of `4 \times N_b` matrices corresponding to the
          expanded key. The `n` th entry of the list corresponds to the matrix
          used in the ``add_round_key`` step of the `n` th round.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 6)
            sage: key = '331D0084B176C3FB59CAA0EDA271B565BB5D9A2D1E4B2892'
            sage: key_state = rgf._hex_to_GF(key)
            sage: key_schedule = rgf.expand_key(key_state)
            sage: rgf._GF_to_hex(key_schedule[0])
            '331d0084b176c3fb59caa0eda271b565'
            sage: rgf._GF_to_hex(key_schedule[6])
            '5c5d51c4121f018d0f4f3e408ae9f78c'
        """
        msg = "keyword '{0}' must be a {1} x {2} matrix over GF({3})"
        msg = msg.format(key, 4, self._Nk, self._F.order())
        if not isinstance(key, Matrix) or \
           not (key.base_ring().is_field() and \
                key.base_ring().is_finite() and \
                key.base_ring().order() == self._F.order()) or \
           not key.dimensions() == (4, self._Nk):
            raise TypeError(msg)

        def add_cols(col1, col2):
            return [x + y for x, y in zip(col1, col2)]

        key_cols = []
        for i in range(self._Nb * (self._Nr + 1)):
            key_cols.append([])

        # Copy columns from ``key``, then build the rest of the columns
        for j in range(self._Nk):
            key_cols[j] = list(key.columns()[j])
        for j in range(self._Nk, self._Nb * (self._Nr + 1)):
            if j % self._Nk == 0:
                # Apply non-linear function to k[j - 1]
                add_key = map(self._srd, key_cols[j - 1])
                add_key = add_key[1:] + add_key[:1]
                add_key[0] += self._F.gen() ** (int(j / self._Nk) - 1)
                key_cols[j] = add_cols(key_cols[j - self._Nk], add_key)
            else:
                add_key = key_cols[j - 1]
                if self._Nk > 6 and j % self._Nk == 4:
                    add_key = map(self._srd, add_key)
                key_cols[j] = add_cols(key_cols[j - self._Nk], add_key)

        # Copy the expanded columns into 4xNb blocks
        round_keys = []
        for r in range(self._Nr + 1):
            rk = column_matrix([key_cols[r*self._Nb + i]
                                for i in range(self._Nb)])
            round_keys.append(rk)
        return round_keys

    def expand_key_poly(self, row, col, round):
        r"""
        Returns a polynomial representing the ``row,col`` th entry of the
        ``round`` th round key.

        INPUT:

        - ``row`` -- The row position of the element represented by this
          polynomial.

        - ``col`` -- The column position of the element represented by this
          polynomial.

        OUTPUT:

        - A polynomial representing the ``row,col`` th entry of the ``round``
          th round key in terms of entries of the input key.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: rgf.expand_key_poly(1, 2, 0)
            k012
            sage: rgf.expand_key_poly(1, 2, 1)
            (x^2 + 1)*k023^254 +
            (x^3 + 1)*k023^253 +
            (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*k023^251 +
            (x^5 + x^2 + 1)*k023^247 +
            (x^7 + x^6 + x^5 + x^4 + x^2)*k023^239 +
            k023^223 +
            (x^7 + x^5 + x^4 + x^2 + 1)*k023^191 +
            (x^7 + x^3 + x^2 + x + 1)*k023^127 +
            k010 +
            k011 +
            k012 +
            (x^6 + x^5 + x)

        It should be noted that ``expand_key_poly`` cannot be used with
        ``apply_poly`` or ``compose``, since ``expand_key_poly`` is not a
        ``Round_Component_Poly_Constr`` object. ::

            sage: rgf.compose(rgf.sub_bytes_poly_constr(), rgf.expand_key_poly)
            Traceback (most recent call last):
            ...
            TypeError: keyword 'g' must be a Round_Component_Poly_Constr or a polynomial over Finite Field in x of size 2^8
            <BLANKLINE>
            sage: state = rgf._hex_to_GF('00000000000000000000000000000000')
            sage: rgf.apply_poly(state, rgf.expand_key_poly)
            Traceback (most recent call last):
            ...
            TypeError: keyword 'poly_constr' must be a Round_Component_Poly_Constr
        """
        if row not in range(4):
            raise ValueError("keyword 'row' must be between 0 and 4")
        if col not in range(self._Nb):
            msg = "keyword 'col' must be between 0 and {0}"
            raise ValueError(msg.format(self._Nb))
        if round not in range(self._Nr + 1):
            msg = "keyword 'r' must be between 0 and {0}"
            raise ValueError(msg.format(self._Nr))

        key_col = round * self._Nb + col
        if key_col < self._Nk:
            return self.key_vrs[row, key_col]
        else:
            if key_col % self._Nk == 0 or \
               (self._Nk > 6 and col % self._Nk == 4):
                # Apply non-linear transformation to key_col - 1
                recur_r = int((key_col - 1)/self._Nb)
                recur_j = (key_col - 1) - (recur_r * self._Nb)
                non_linear = self.expand_key_poly((row+1) % 4,
                                                  recur_j, recur_r)
                non_linear = self._srd(non_linear)
                non_linear += self._F.gen() ** (int(key_col / self._Nk) - 1)
                # Identify key_col - Nk
                recur_r = int((key_col - self._Nk)/self._Nb)
                recur_j = (key_col - self._Nk) - (recur_r * self._Nb)
                return self.expand_key_poly(row, recur_j, recur_r) + non_linear
            else:
                # Identify key_col - Nk
                recur_r = int((key_col - self._Nk)/self._Nb)
                recur_j = (key_col - self._Nk) - (recur_r * self._Nb)
                result = self.expand_key_poly(row, recur_j, recur_r)
                # Identify key_col - 1
                recur_r = int((key_col- 1)/self._Nb)
                recur_j = (key_col - 1) - (recur_r * self._Nb)
                return result + \
                       self.expand_key_poly(row, recur_j, recur_r)

    def apply_poly(self, state, poly_constr, algorithm='encrypt', keys=None,
                   poly_constr_attr=None):
        r"""
        Returns a state matrix where ``poly_method`` is applied to each entry.

        INPUT:

        - ``state`` -- The state matrix over `\GF{2^8}` to which
          ``poly_method`` is applied to.

        - ``poly_constr`` -- The ``Round_Component_Poly_Constr`` object to
          build polynomials during evaluation.

        - ``algorithm`` -- (default: "encrypt") Passed directly to
          ``rcpc`` to select encryption or decryption. The
          encryption flag is "encrypt" and the decrypt flag is "decrypt".

        - ``keys`` -- (default: None) An array of `N_r` subkey matrices to
          replace any key variables in any polynomials returned by
          ``poly_method``. Must be identical to the format returned by
          ``expand_key``. If any polynomials have key variables and ``keys``
          is not supplied, the key variables will remain as-is.

        - ``poly_constr_attr`` -- (default:None) A dictionary of keyword
          attributes to pass to ``rcpc`` when it is called.

        OUTPUT:

        - A state matrix in `\GF{2^8}` whose `i,j` th entry equals the
          polynomial ``poly_constr(i, j, algorithm, **poly_constr_attr)``
          evaluated by setting its variables equal to the corresponding
          entries of ``state``.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: state = rgf._hex_to_GF('3b59cb73fcd90ee05774222dc067fb68')
            sage: result = rgf.apply_poly(state, rgf.shift_rows_poly_constr())
            sage: rgf._GF_to_hex(result)
            '3bd92268fc74fb735767cbe0c0590e2d'

        Calling ``apply_poly`` with the ``Round_Component_Poly_Constr`` object
        of a round component (e.g. ``sub_bytes_poly``) is identical to
        calling that round component function itself. ::

            sage: state = rgf._hex_to_GF('4915598f55e5d7a0daca94fa1f0a63f7')
            sage: apply_poly_result = rgf.apply_poly(state,
            ....: rgf.sub_bytes_poly_constr())
            sage: direct_result = rgf.sub_bytes(state)
            sage: direct_result == apply_poly_result
            True

        If the ``Round_Component_Poly_Constr`` object's ``__call__`` method
        returns a polynomial with state variables as well as key variables, we
        can supply a list of `N_r` round keys ``keys`` whose elements are
        evaluated as the key variables. If this is not provided, the key
        variables will remain as is.::

            sage: state = rgf._hex_to_GF('14f9701ae35fe28c440adf4d4ea9c026')
            sage: key = rgf._hex_to_GF('54d990a16ba09ab596bbf40ea111702f')
            sage: keys = rgf.expand_key(key)
            sage: result = rgf.apply_poly(state,
            ....: rgf.add_round_key_poly_constr(), keys=keys)
            sage: result == rgf.add_round_key(state, key)
            True
            <BLANKLINE>
            sage: rgf.apply_poly(state, rgf.add_round_key_poly_constr())[0,0]
            k000 + (x^4 + x^2)

        We can change the value of the keywords of ``poly_constr`` 's
        ``__call__`` method when ``apply_poly`` calls it by passing in a
        dictionary ``poly_constr_attr`` mapping keywords to their values. ::

            sage: rgf.apply_poly(rgf.state_vrs,
            ....: rgf.add_round_key_poly_constr(),
            ....: poly_constr_attr={'round' : 5})
            [a00 + k500 a01 + k501 a02 + k502 a03 + k503]
            [a10 + k510 a11 + k511 a12 + k512 a13 + k513]
            [a20 + k520 a21 + k521 a22 + k522 a23 + k523]
            [a30 + k530 a31 + k531 a32 + k532 a33 + k533]
        """
        self._check_valid_PRmatrix(state, 'state')
        if not isinstance(poly_constr, RijndaelGF.Round_Component_Poly_Constr):
            msg = "keyword 'poly_constr' must be a Round_Component_Poly_Constr"
            raise TypeError(msg)
        if keys is not None and (not isinstance(keys, list) or \
           len(keys) != self._Nr + 1 or \
           not all([isinstance(k, Matrix) for k in keys]) or \
           not all([k.dimensions() == (4, self._Nb) for k in keys]) or \
           not all([k.base_ring().is_finite() and k.base_ring().is_field()
                    and k.base_ring().order() == 256 for k in keys]) ):
            msg = ("keys must be a length {0} array of 4 by {1} matrices"
                   " over {2}")
            raise TypeError(msg.format(self._Nr, self._Nb, self._F))

        output = []
        if keys is not None:
            key_list = [el for inner in keys for el in inner.list()]
        for i in range(4):
            for j in range(self._Nb):
                # this is to combat a major performance issue caused by
                # subbytes' inversion transformation.
                if poly_constr == self.sub_bytes_poly_constr() and \
                   algorithm == 'decrypt':
                    p = poly_constr(i, j, algorithm, no_inversion=True)
                    p = p(state.list()) ** 254
                else:
                    if poly_constr_attr is None:
                        p = poly_constr(i, j, algorithm)
                    else:
                        p = poly_constr(i, j, algorithm, **poly_constr_attr)
                    # If there are key variables in the polynomial
                    if len(p.args()) > 4 * self._Nb:
                        if keys is not None:
                            p = p(state.list() + key_list)
                        else:
                            p = p(state.list() + self.subkey_vrs_list)
                    else:
                        p = p(state.list())
                output.append(p)
        return matrix(4, 4, output)

    def compose(self, f, g, algorithm='encrypt', f_attr=None, g_attr=None):
        r"""
        Return a ``Round_Component_Poly_Constr`` object corresponding to
        `g \circ f` or the polynomial output of this object's ``__call__``
        method.

        INPUT:

        - ``f`` -- A ``Round_Component_Poly_Constr`` object corresponding to
          a round component function `f`.

        - ``g`` -- A ``Round_Component_Poly_Constr`` object corresponding to
          a round component function `g` or a polynomial output of this
          object's ``__call__`` method.

        - ``algorithm`` -- (default: "encrypt") Whether ``f`` and ``g``
          should use their encryption transformations or their decryption
          transformations. Does nothing if ``g`` is a
          ``Round_Component_Poly_Constr`` object. The encryption flag is
          "encrypt" and the decryption flag is "decrypt".

        - ``f_attr`` -- (default: None) A dictionary of keyword attributes to
          pass to ``f`` when it is called.

        - ``g_attr`` -- (default: None) A dictionary of keyword attributes to
          pass to ``g`` when it is called. Does nothing if ``g`` is a
          polynomial.

        OUTPUT:

        - If ``g`` is a ``Round_Component_Poly_Constr`` object corresponding
          to a round component function `g`, then ``compose`` returns a
          ``Round_Component_Poly_Constr`` corresponding to the round
          component function `g \circ f`, where `f` is the round component
          function corresponding to the first argument ``f``. On the other
          hand, if ``g`` `= g(A)_{i,j}` for a round component function `g`,
          then ``compose`` returns `g(f(A))_{i,j}`, where `A` is an
          arbitrary input state matrix.

        EXAMPLES

        This function allows us to determine the polynomial representations
        of entries across multiple round functions. For example, if we
        wanted a polynomial representing the ``1,3`` entry of a matrix after
        we first apply ShiftRows and then MixColumns to that matrix, we do::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: mcp = rgf.mix_columns_poly_constr()(1, 3); mcp
            a03 + (x)*a13 + (x + 1)*a23 + a33
            sage: result = rgf.compose(rgf.shift_rows_poly_constr(), mcp)
            sage: result
            a03 + (x)*a10 + (x + 1)*a21 + a32

        We can test the correctness of this::

            sage: state = rgf._hex_to_GF('fa636a2825b339c940668a3157244d17')
            sage: new_state = rgf.shift_rows(state)
            sage: new_state = rgf.mix_columns(new_state)
            sage: result(state.list()) == new_state[1,3]
            True

        We can also use ``compose`` to build a new
        ``Round_Component_Poly_Constr`` object corresponding to the composition
        of multiple round functions as such::

            sage: fn = rgf.compose(rgf.shift_rows_poly_constr(),
            ....: rgf.mix_columns_poly_constr())
            sage: fn(1, 3)
            a03 + (x)*a10 + (x + 1)*a21 + a32

        If we use ``compose`` to make a new ``Round_Component_Poly_Constr``
        object, we can use that object as input to ``apply_poly`` and
        ``compose``::

            sage: state = rgf._hex_to_GF('36400926f9336d2d9fb59d23c42c3950')
            sage: result = rgf.apply_poly(state, fn)
            sage: rgf._GF_to_hex(result)
            'f4bcd45432e554d075f1d6c51dd03b3c'
            <BLANKLINE>
            sage: new_state = rgf.shift_rows(state)
            sage: new_state = rgf.mix_columns(new_state)
            sage: result == new_state
            True

        ::

            sage: fn2 = rgf.compose(rgf.sub_bytes_poly_constr(), fn)

        If the second argument is a polynomial, then the value of ``algorithm``
        is passed directly to the first argument `f` during evaluation.
        However, if the second argument is a ``Round_Component_Poly_Constr``
        object, changing ``algorithm`` does nothing since the returned object
        has its own ``algorithm='encrypt'`` keyword. ::

            sage: f = rgf.compose(rgf.sub_bytes_poly_constr(),
            ....: rgf.mix_columns_poly_constr(), algorithm='decrypt')
            sage: g = rgf.compose(rgf.sub_bytes_poly_constr(),
            ....: rgf.mix_columns_poly_constr())
            sage: all([f(i,j) == g(i,j) for i in range(4) for j in range(4)])
            True

        We can change the keyword attributes of the ``__call__`` methods of
        ``f`` and ``g`` by passing dictionaries ``f_attr`` and ``g_attr`` to
        ``compose``. ::

            sage: fn = rgf.compose(rgf.add_round_key_poly_constr(),
            ....: rgf.add_round_key_poly_constr(),
            ....: f_attr={'round' : 4}, g_attr={'round' : 7})
            sage: fn(1, 2)
            a12 + k412 + k712
        """
        if not isinstance(f, RijndaelGF.Round_Component_Poly_Constr):
            msg = "keyword 'f' must be a Round_Component_Poly_Constr"
            raise TypeError(msg)
        from sage.rings.polynomial.multi_polynomial import is_MPolynomial
        if not isinstance(g, RijndaelGF.Round_Component_Poly_Constr) and \
           not is_MPolynomial(g):
            msg = ("keyword 'g' must be a Round_Component_Poly_Constr or a "
                   "polynomial over {0}")
            raise TypeError(msg.format(self._F))
        if f_attr is not None and not isinstance(f_attr, dict):
            raise TypeError("f_attr must be a dictionary of keywords for f")
        if g_attr is not None and not isinstance(g_attr, dict):
            raise TypeError("g_attr must be a dictionary of keywords for g")

        if g in self._all_PR:
            if isinstance(f_attr, dict):
                f_vals = [f(i, j, algorithm, **f_attr)
                          for i in range(4) for j in range(self._Nb)]
            else:
                f_vals = [f(i, j, algorithm)
                          for i in range(4) for j in range(self._Nb)]
            if g in self._state_PR:
                return g(f_vals)
            else:
                return g(f_vals + self.subkey_vrs_list)
        else:
            if isinstance(g_attr, dict):
                lm = lambda i, j, alg='encrypt' : \
                self.compose(f, g(i, j, alg, **g_attr), alg, f_attr, g_attr)
            else:
                lm = lambda i, j, alg='encrypt' : \
                     self.compose(f, g(i, j, alg), alg, f_attr, g_attr)
            return RijndaelGF.Round_Component_Poly_Constr(lm, self)

    def add_round_key_poly_constr(self):
        r"""
        Return the ``Round_Component_Poly_Constr`` object corresponding to
        AddRoundKey.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: ark_pc = rgf.add_round_key_poly_constr()
            sage: ark_pc
            A polynomial constructor for the function 'Add Round Key' of Rijndael-GF block cipher with block length 4, key length 4, and 10 rounds.
            sage: ark_pc(0, 1)
            a01 + k001

        When invoking the returned object's ``__call__`` method, changing the
        value of ``algorithm='encrypt'`` does nothing, since the AddRoundKey
        round component function is its own inverse. ::

            sage: with_encrypt = ark_pc(1, 1, algorithm='encrypt')
            sage: with_decrypt = ark_pc(1, 1, algorithm='decrypt')
            sage: with_encrypt == with_decrypt
            True

        When invoking the returned object's ``__call__`` method, one can change
        the round subkey used in the returned polynomial by changing the
        ``round=0`` keyword. ::

            sage: ark_pc(2, 1, round=7)
            a21 + k721

        When passing the returned object to methods such as ``apply_poly`` and
        ``compose``, we can make these methods use a non-default value for
        ``round=0`` by passing in a dictionary mapping ``round`` to a different
        value. ::

            sage: rgf.apply_poly(rgf.state_vrs, ark_pc,
            ....: poly_constr_attr={'round' : 6})
            [a00 + k600 a01 + k601 a02 + k602 a03 + k603]
            [a10 + k610 a11 + k611 a12 + k612 a13 + k613]
            [a20 + k620 a21 + k621 a22 + k622 a23 + k623]
            [a30 + k630 a31 + k631 a32 + k632 a33 + k633]

        ::

            sage: rcpc = rgf.compose(ark_pc, ark_pc,
            ....: f_attr={'round' : 3}, g_attr={'round' : 5})
            sage: rcpc(3, 1)
            a31 + k331 + k531
        """
        return self._add_round_key_rcpc

    def _add_round_key_pc(self, row, col, algorithm='encrypt', round=0):
        r"""
        Returns a polynomial representing an element of a round-key addition.

        INPUT:

        - ``row`` -- The row number of the entry represented by this method's
          output.

        - ``col`` -- The column number of the entry represented by this
          method's output.

        - ``algorithm`` -- (default: "encrypt") Whether to return the
          polynomial as an encryption or as a decryption. The encryption flag
          is "encrypt" and the decryption  flag is "decrypt".

        - ``round`` -- (default: 0) The round number of the entry represented
          by this method's output.

        OUTPUT:

        - A polynomial representing the ``row,col`` th entry of a state matrix
          after a round-key addition in terms of entries of the input state
          matrix and entries of the ``round`` th round key.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: rgf._add_round_key_pc(1, 2, round=7)
            a12 + k712

        As expected, since the encryption and decryption transformations are
        identical, changing ``algorithm`` has no effect.

            sage: with_encrypt = rgf._add_round_key_pc(3, 2,
            ....: 'encrypt')
            sage: with_decrypt = rgf._add_round_key_pc(3, 2,
            ....: 'decrypt')
            sage: with_encrypt == with_decrypt
            True
        """
        if round not in range(self._Nr):
            msg = "keyword 'round' must be between 0 and {0}"
            raise ValueError(msg.format(self._Nr))
        state_var = self.state_vrs[row, col]
        key_var = self.subkey_vrs[round][row, col]
        return state_var + key_var

    def add_round_key(self, state, round_key):
        r"""
        Returns the round-key addition of matrices ``state`` and ``round_key``.

        INPUT:

        - ``state`` -- The state matrix to have ``round_key`` added to.

        - ``round_key`` -- The round key to add to ``state``.

        OUTPUT:

        - A state matrix which is the round key addition of ``state`` and
          ``round_key``. This transformation is simply the entrywise addition
          of these two matrices.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: state = rgf._hex_to_GF('36339d50f9b539269f2c092dc4406d23')
            sage: key = rgf._hex_to_GF('7CC78D0E22754E667E24573F454A6531')
            sage: key_schedule = rgf.expand_key(key)
            sage: result = rgf.add_round_key(state, key_schedule[0])
            sage: rgf._GF_to_hex(result)
            '4af4105edbc07740e1085e12810a0812'
        """
        self._check_valid_PRmatrix(state, 'state')
        self._check_valid_PRmatrix(round_key, 'round_key')
        # We don't use apply_poly here since that would require giving this
        # method an extra argument of a round number
        return state + round_key

    def sub_bytes_poly_constr(self):
        r"""
        Return the ``Round_Component_Poly_Constr`` object corresponding to
        SubBytes.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: sb_pc = rgf.sub_bytes_poly_constr()
            sage: sb_pc
            A polynomial constructor for the function 'SubBytes' of Rijndael-GF block cipher with block length 4, key length 4, and 10 rounds.
            sage: sb_pc(2, 3)
            (x^2 + 1)*a23^254 +
            (x^3 + 1)*a23^253 +
            (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a23^251 +
            (x^5 + x^2 + 1)*a23^247 +
            (x^7 + x^6 + x^5 + x^4 + x^2)*a23^239 +
            a23^223 +
            (x^7 + x^5 + x^4 + x^2 + 1)*a23^191 +
            (x^7 + x^3 + x^2 + x + 1)*a23^127 +
            (x^6 + x^5 + x + 1)

        The returned object's ``__call__`` method has an additional keyword
        of ``no_inversion=False``, which causes the returned polynomial to
        represent only the affine transformation step of SubBytes. ::

            sage: sb_pc(1, 0, no_inversion=True)
            (x^7 + x^3 + x^2 + x + 1)*a10^128 +
            (x^7 + x^5 + x^4 + x^2 + 1)*a10^64 +
            a10^32 +
            (x^7 + x^6 + x^5 + x^4 + x^2)*a10^16 +
            (x^5 + x^2 + 1)*a10^8 +
            (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a10^4 +
            (x^3 + 1)*a10^2 +
            (x^2 + 1)*a10 +
            (x^6 + x^5 + x + 1)

        We can build a polynomial representing the inverse transformation
        by setting the keyword ``algorithm='decrypt'``. However, the order of
        the affine transformation and the inversion step in SubBytes means that
        this polynomial has thousands of terms and is very slow to compute.
        Hence, if one wishes to build the decryption polynomial with the
        intention of evaluating that polynomial for a particular input, it is
        strongly recommended to first call
        ``sb_pc(i, j, algorithm='decrypt', no_inversion=True)`` to build a
        polynomial representing only the inverse affine transformation,
        evaluate this polynomial for your intended input, then finally
        calculate the inverse of the result. ::

            sage: poly = sb_pc(1, 2, algorithm='decrypt', no_inversion=True)
            sage: state = rgf._hex_to_GF('39daee38f4f1a82aaf432410c36d45b9')
            sage: result = poly(state.list())
            sage: rgf._GF_to_hex(result * -1)
            '49'

        When passing the returned object to ``apply_poly`` and ``compose``, we
        can make those methods change the keyword ``no_inversion`` of this
        object's ``__call__`` method by passing the dictionary
        ``{'no_inversion' : True}`` to them. ::

            sage: result = rgf.apply_poly(state, sb_pc,
            ....: poly_constr_attr={'no_inversion' : True})
            sage: rgf._GF_to_hex(result)
            '961c72894526f746aa85fc920adcc719'

        ::

            sage: rcpc = rgf.compose(sb_pc, rgf.shift_rows_poly_constr(),
            ....: f_attr={'no_inversion' : True})

        Note that if we set ``algorithm='decrypt'`` for ``apply_poly``, it
        will perform the necessary performance enhancement described above
        automatically. The structure of ``compose``, however, unfortunately
        does not allow this enhancement to be employed.
        """
        return self._sub_bytes_rcpc

    def _sub_bytes_pc(self, row, col, algorithm='encrypt', no_inversion=False):
        r"""
        Returns a polynomial representing `SubBytes(A)_{\textit{row, col}}`.

        INPUT:

        - ``row`` -- The row number of the entry represented by this method's
          output.

        - ``col`` -- The column number of the entry represented by this
          method's output.

        - ``algorithm`` -- (default: "encrypt") Whether to return the
          polynomial as an encryption or as a decryption. The encryption flag
          is "encrypt" and the decryption  flag is "decrypt".

        - ``no_inversion`` -- (default: ``False``) Don't perform the inversion
          step, only perform the affine transformation. Primarily intended
          to increase performance during decryption, as is shown in the
          below example.

        OUTPUT:

        - A polynomial representing the ``row,col`` th entry of a state matrix
          after the SubBytes method has been applied to it.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: rgf._sub_bytes_pc(2, 3)
            (x^2 + 1)*a23^254 + (x^3 + 1)*a23^253 + (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a23^251 + (x^5 + x^2 + 1)*a23^247 + (x^7 + x^6 + x^5 + x^4 + x^2)*a23^239 + a23^223 + (x^7 + x^5 + x^4 + x^2 + 1)*a23^191 + (x^7 + x^3 + x^2 + x + 1)*a23^127 + (x^6 + x^5 + x + 1)

        We can use this polynomial to calculate individual entries of the
        output matrix for any given state as such::

            sage: state = rgf._hex_to_GF('6385b79ffc538df997be478e7547d691')
            sage: poly = rgf._sub_bytes_pc(2, 3)
            sage: poly(state.list())
            x^7 + x^6 + x^5 + x^4 + x^2 + x

        We can set ``no_inversion`` to ``True`` to get a polynomial
        representation of solely the affine transformation. ::

            sage: rgf._sub_bytes_pc(0, 2, no_inversion=True)
            (x^7 + x^3 + x^2 + x + 1)*a02^128 + (x^7 + x^5 + x^4 + x^2 + 1)*a02^64 + a02^32 + (x^7 + x^6 + x^5 + x^4 + x^2)*a02^16 + (x^5 + x^2 + 1)*a02^8 + (x^7 + x^6 + x^5 + x^4 + x^3 + 1)*a02^4 + (x^3 + 1)*a02^2 + (x^2 + 1)*a02 + (x^6 + x^5 + x + 1)

        When generating a decryption polynomial, calculating the inverse of
        the polynomial representing the affine transformation can be a very
        slow process. In order to speed up decryption when applying
        ``sub_bytes_poly`` to a state matrix, it is recommended to calculate
        the decryption polynomial with ``no_inversion=True``, evaluate the
        arguments, then perform the inversion after this result has been
        calculated. ::

            sage: poly = rgf._sub_bytes_pc(0, 0,
            ....: algorithm='decrypt', no_inversion=True)
            sage: state = rgf._hex_to_GF('b415f8016858552e4bb6124c5f998a4c')
            sage: poly(state.list()) ^ -1
            x^7 + x^6 + x^2 + x
        """
        if algorithm == 'encrypt':
            var = self.state_vrs[row, col]
            coeffs = self._sb_E_coeffs
            if no_inversion:
                return sum([coeffs[i] * (var**(2**i))
                            for i in range(8)]) + self._F("x^6 + x^5 + x + 1")
            else:
                return sum([coeffs[i] * (var**(255 - 2**i))
                            for i in range(8)]) + self._F("x^6 + x^5 + x + 1")
        elif algorithm == 'decrypt':
            var = self.state_vrs[row, col]
            coeffs = self._sb_D_coeffs
            result = (sum([coeffs[i] * var**(2**i) for i in range(8)]) + \
                        self._F("x^2 + 1"))
            if no_inversion:
                return result
            else:
                return result ** 254
        else:
            raise ValueError(("keyword 'algorithm' must be either 'encrypt' "
                             "or 'decrypt'"))

    def _srd(self, el, algorithm='encrypt'):
        r"""
        Returns the application of SubBytes (`S_{RD}`) to ``el``.

        INPUT:

        - ``el`` -- An element of `\GF{2^8}`.

        - ``algorithm`` -- (default: "encrypt") Whether to perform the
          encryption transformation or the decryption transformation.
          The encryption flag is "encrypt" and the decryption flag is
          "decrypt".

        OUTPUT:

        - The result of the application of the non-linear transformation
          SubBytes to ``el``.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: el = rgf._hex_to_GF('2A', matrix=False)[0]
            sage: rgf._srd(el)
            x^7 + x^6 + x^5 + x^2 + 1
        """
        if algorithm == 'encrypt':
            p = self._sub_bytes_rcpc(0, 0, algorithm)
            state = [el] + [self._F.zero()]*((4 * self._Nb)-1)
            return p(state)
        elif algorithm == 'decrypt':
            p = self._sub_bytes_rcpc(0, 0, algorithm, no_inversion=True)
            state = [el] + [self._F.zero()]*((4 * self._Nb)-1)
            return p(state) ** 254
        else:
            raise ValueError(("keyword 'algorithm' must be either 'encrypt' "
                             "or 'decrypt'"))

    def sub_bytes(self, state, algorithm='encrypt'):
        r"""
        Returns the application of SubBytes to the state matrix ``state``.

        INPUT:

        - ``state`` -- The state matrix to apply SubBytes to.

        - ``algorithm`` -- (default: "encrypt") Whether to apply the
          encryption step of SubBytes or its decryption inverse. The encryption
          flag is "encrypt" and the decryption flag is "decrypt".

        OUTPUT:

        - The state matrix over `\GF{2^8}` where SubBytes has been applied
          to every entry of ``state``.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: state = rgf._hex_to_GF('d1c4941f7955f40fb46f6c0ad68730ad')
            sage: result = rgf.sub_bytes(state)
            sage: rgf._GF_to_hex(result)
            '3e1c22c0b6fcbf768da85067f6170495'
            sage: decryption = rgf.sub_bytes(result, algorithm='decrypt')
            sage: decryption == state
            True
        """
        self._check_valid_PRmatrix(state, 'state')
        return self.apply_poly(state, self._sub_bytes_rcpc, algorithm)

    def mix_columns_poly_constr(self):
        r"""
        Return a ``Round_Component_Poly_Constr`` object corresponding to
        MixColumns.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: mc_pc = rgf.mix_columns_poly_constr()
            sage: mc_pc
            A polynomial constructor for the function 'Mix Columns' of Rijndael-GF block cipher with block length 4, key length 4, and 10 rounds.
            sage: mc_pc(1, 2)
            a02 + (x)*a12 + (x + 1)*a22 + a32
            sage: mc_pc(1, 0, algorithm='decrypt')
            (x^3 + 1)*a00 + (x^3 + x^2 + x)*a10 + (x^3 + x + 1)*a20 + (x^3 + x^2 + 1)*a30

        The returned object's ``__call__`` method has no additional keywords,
        unlike ``sub_bytes_poly_constr()`` and ``add_round_key_poly_constr()``.
        """
        return self._mix_columns_rcpc

    def _mix_columns_pc(self, row, col, algorithm='encrypt'):
        r"""
        Returns a polynomial representing `MixColumns(A)_{\textit{row, col}}`.

        INPUT:

        - ``row`` -- The row number of the entry represented by this method's
          output.

        - ``col`` -- The column number of the entry represented by this
          method's output.

        - ``algorithm`` -- (default: "encrypt") Whether to perform the
          encryption transformation or the decryption transformation. The
          encryption flag is "encrypt" and the decryption flag is "decrypt".

        OUTPUT:

        - A polynomial in terms of entries of the input state matrix which
          represents the ``row,col`` th entry of the output matrix after
          MixColumns has been applied to it.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: rgf._mix_columns_pc(3, 1)
            (x + 1)*a01 + a11 + a21 + (x)*a31

        We can use this to calculate individual entries of a state matrix after
        the decryption version of MixColumns has been applied to it as such::

            sage: poly = rgf._mix_columns_pc(2, 2, algorithm='decrypt')
            sage: state = rgf._hex_to_GF('a761ca9b97be8b45d8ad1a611fc97369')
            sage: result = poly(state.list())
            sage: rgf._GF_to_hex(result)
            'b7'
            sage: output = rgf.mix_columns(state, algorithm='decrypt')
            sage: output[2,2] == result
            True
        """
        if algorithm == 'encrypt':
            coeffs = self._mixcols_E
        elif algorithm == 'decrypt':
            coeffs = self._mixcols_D
        else:
            raise ValueError(("keyword 'algorithm' must be either 'encrypt' "
                             "or 'decrypt'"))
        return sum([coeffs[row,k] * self.state_vrs[k,col] for k in range(4)])

    def mix_columns(self, state, algorithm='encrypt'):
        r"""
        Returns the application of MixColumns to the state matrix ``state``.

        INPUT:

        - ``state`` -- The state matrix to apply MixColumns to.

        - ``algorithm`` -- (default: "encrypt") Whether to perform the
          encryption version of MixColumns, or its decryption inverse. The
          encryption flag is "encrypt" and the decryption flag is "decrypt".

        OUTPUT:

        - The state matrix over `\GF{2^8}` which is the result of applying
          MixColumns to ``state``.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: state = rgf._hex_to_GF('cd54c7283864c0c55d4c727e90c9a465')
            sage: result = rgf.mix_columns(state)
            sage: rgf._GF_to_hex(result)
            '921f748fd96e937d622d7725ba8ba50c'
            sage: decryption = rgf.mix_columns(result, algorithm='decrypt')
            sage: decryption == state
            True
        """
        self._check_valid_PRmatrix(state, 'state')
        return self.apply_poly(state, self._mix_columns_rcpc, algorithm)

    def shift_rows_poly_constr(self):
        r"""
        Return a ``Round_Component_Poly_Constr`` object corresponding to
        ShiftRows.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: sr_pc = rgf.shift_rows_poly_constr()
            sage: sr_pc(3, 0)
            a33
            sage: sr_pc(2, 1, algorithm='decrypt')
            a23

        The returned object's ``__call__`` method has no additional keywords,
        unlike ``sub_bytes_poly_constr()`` and ``add_round_key_poly_constr``.
        """
        return self._shift_rows_rcpc

    def _shift_rows_pc(self, row, col, algorithm='encrypt'):
        r"""
        Returns a polynomial representing `ShiftRows(A)_{\textit{row,col}}`.

        INPUT:

        - ``row`` -- The row number of the entry represented by this method's
          output.

        - ``col`` -- The column number of the entry represented by this
          method's output.

        - ``algorithm`` -- (default: "encrypt") Whether to perform ShiftRows'
          encryption step or its decryption inverse. The encryption flag is
          "encrypt" and the decryption flag is "decrypt".

        OUTPUT:

        - A polynomial in terms of entries of the input state matrix which
          represents the ``row,col`` th entry of the output matrix after
          ShiftRows has been applied to it.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: rgf._shift_rows_pc(2, 3)
            a21

        We can use this to calculate individual entries of a state matrix
        after the decryption version of ShiftRows has been applied to it as
        such::

            sage: poly = rgf._shift_rows_pc(2, 3, algorithm='decrypt')
            sage: state = rgf._hex_to_GF('78c4f708318d3cd69655b701bfc093cf')
            sage: result = poly(state.list())
            sage: rgf._GF_to_hex(result)
            '3c'
            sage: output = rgf.shift_rows(state, algorithm='decrypt')
            sage: output[2,3] == result
            True
        """
        if algorithm == 'encrypt':
            offs = self._shiftrows_offsets_E
        elif algorithm == 'decrypt':
            offs = self._shiftrows_offsets_D
        else:
            raise ValueError(("keyword 'algorithm' must be either 'encrypt' "
                             "or 'decrypt'"))
        return self.state_vrs[row, (col + offs[4 - self._Nb][row]) % 4]

    def shift_rows(self, state, algorithm='encrypt'):
        r"""
        Returns the application of ShiftRows to the state matrix ``state``.

        INPUT:

        - ``state`` -- A state matrix over `\GF{2^8}` to which ShiftRows is
          applied to.

        - ``algorithm`` -- (default: "encrypt") Whether to perform the
          encryption version of ShiftRows or its decryption inverse. The
          encryption flag is "encrypt" and the decryption flag is "decrypt".

        OUTPUT:

        - A state matrix over `\GF{2^8}` which is the application of ShiftRows
          to ``state``.

        EXAMPLES::

            sage: from sage.crypto.mq.rijndael_gf import RijndaelGF
            sage: rgf = RijndaelGF(4, 4)
            sage: state = rgf._hex_to_GF('adcb0f257e9c63e0bc557e951c15ef01')
            sage: result = rgf.shift_rows(state)
            sage: rgf._GF_to_hex(result)
            'ad9c7e017e55ef25bc150fe01ccb6395'
            sage: decryption = rgf.shift_rows(result, algorithm='decrypt')
            sage: decryption == state
            True
        """
        self._check_valid_PRmatrix(state, 'state')
        return self.apply_poly(state, self._shift_rows_rcpc, algorithm)

    class Round_Component_Poly_Constr(SageObject):

        def __init__(self, polynomial_constr, rgf, round_component_name=None):
            r"""
            An object which constructs polynomials representing round
            component functions of a RijndaelGF object.

            INPUT:

            - ``polynomial_constr`` -- A function which takes an index
              ``row,col`` and returns a polynomial representing the ``row,col``
              th entry of a matrix after a specific round component function
              has been applied to it. This polynomial must be in terms of
              entries of the input matrix to that round component function and
              of entries of various subkeys. ``polynomial_constr`` must have
              arguments of the form ``polynomial_constr(row, col,
              algorithm='encrypt', **kwargs)`` and  must be able to be called
              as ``polynomial_constr(row, col)``.

            - ``rgf`` -- The RijndaelGF object whose state entries are
              represented by polynomials returned from ``polynomial_constr``.

            - ``round_component_name`` -- The name of the round component
              function this object corresponds to as a string. Used solely
              for display purposes.

            EXAMPLES::

                sage: from sage.crypto.mq.rijndael_gf import \
                ....: RijndaelGF
                sage: rgf = RijndaelGF(4, 4)
                sage: rcpc = RijndaelGF.Round_Component_Poly_Constr(
                ....: rgf._shift_rows_pc, rgf, "Shift Rows")
                sage: rcpc
                A polynomial constructor for the function 'Shift Rows' of Rijndael-GF block cipher with block length 4, key length 4, and 10 rounds.

            If `\phi` is the round component function to which this object
            corresponds to, then ``__call__(i,j)`` `= \phi(A)_{i,j}`, where
            `A` is an arbitrary input matrix. Note that the polynomial returned
            by ``__call__(i,j)`` will be in terms of the entries of `A`. ::

                sage: rcpc = RijndaelGF.Round_Component_Poly_Constr(
                ....: rgf._mix_columns_pc, rgf, "Mix Columns")
                sage: poly = rcpc(1, 2); poly
                a02 + (x)*a12 + (x + 1)*a22 + a32
                sage: state = rgf._hex_to_GF('d1876c0f79c4300ab45594add66ff41f')
                sage: result = rgf.mix_columns(state)
                sage: result[1,2] == poly(state.list())
                True

            Invoking this objects ``__call__`` method passes its arguments
            directly to ``polynomial_constr`` and returns the result. In a
            sense, ``Round_Component_Poly_Constr`` acts as a wrapper for
            the ``polynomial_constr`` method and helps ensure that each
            ``Round_Component_Poly_Constr`` object will act similarly. ::

                sage: all([rgf._mix_columns_pc(i, j) == rcpc(i, j)
                ....: for i in range(4) for j in range(4)])
                True

            Since all keyword arguments of ``polynomial_constr`` must have a
            default value except for ``row`` and ``col``, we can always call
            a ``Round_Component_Poly_Constr`` object by ``__call__(row, col)``.
            Because of this, methods such as ``apply_poly`` and ``compose``
            will only call ``__call__(row, col)`` when passed a
            ``Round_Component_Poly_Constr`` object. In order to change this
            object's behavior and force methods such as ``apply_poly`` to use
            non-default values for keywords we can pass dictionaries mapping
            keywords to non-default values as input to ``apply_poly`` and
            ``compose``. ::

                sage: rgf.apply_poly(rgf.state_vrs,
                ....: rgf.add_round_key_poly_constr(),
                ....: poly_constr_attr={'round' : 9})
                [a00 + k900 a01 + k901 a02 + k902 a03 + k903]
                [a10 + k910 a11 + k911 a12 + k912 a13 + k913]
                [a20 + k920 a21 + k921 a22 + k922 a23 + k923]
                [a30 + k930 a31 + k931 a32 + k932 a33 + k933]

            ::

                sage: fn = rgf.compose(rgf.add_round_key_poly_constr(),
                ....: rgf.add_round_key_poly_constr(),
                ....: f_attr={'round' : 3}, g_attr={'round' : 7})
                sage: fn(2, 3)
                a23 + k323 + k723

            Because all ``Round_Component_Poly_Constr`` objects are callable
            as ``__call__(row, col, algorithm)``, ``__call__`` will check
            the validity of these three arguments automatically. Any other
            keywords, however, must be checked in ``polynomial_constr``. ::

                sage: def my_poly_constr(row, col, algorithm='encrypt'):
                ....:     return x * rgf._F.one() # example body with no checks
                ....:
                sage: rcpc = RijndaelGF.Round_Component_Poly_Constr(
                ....: my_poly_constr, rgf, "My Poly Constr")
                sage: rcpc(-1, 2)
                Traceback (most recent call last):
                ...
                ValueError: keyword 'row' must be in range 0 - 3
                sage: rcpc(1, 2, algorithm=5)
                Traceback (most recent call last):
                ...
                ValueError: keyword 'algorithm' must be either 'encrypt' or 'decrypt'
            """
            from inspect import getargspec
            pc_args = getargspec(polynomial_constr)
            if pc_args[0][0] == 'self':
                # Check number of defaulted arguments
                if len(pc_args[3]) != len(pc_args[0]) - 3:
                    msg = ("keyword 'polynomial_constr' must be callable as: "
                           "polynomial_constr(row, col, algorithm='encrypt')")
                    raise TypeError(msg)
            else:
                if len(pc_args[3]) != len(pc_args[0]) - 2:
                    msg = ("keyword 'polynomial_constr' must be callable as: "
                           "polynomial_constr(row, col, algorithm='encrypt')")
                    raise TypeError(msg)
            self._polynomial_constr = polynomial_constr
            self._Nb = rgf.block_length()
            self._rgf_name = rgf.__repr__()
            if round_component_name is not None and \
               not isinstance(round_component_name, str):
                msg = "round_component_name must be None or a string"
                raise TypeError(msg)
            self._rc_name = round_component_name

        def __call__(self, row, col, algorithm='encrypt', **kwargs):
            r"""
            Returns ``polynomial_constr(row, col, algorithm, **attr_dict)``.

            INPUT:

            - ``row`` -- The row number to pass to ``polynomial_constr``.

            - ``col`` -- The column number to pass to ``polynomial_constr``.

            - ``algorithm`` -- (default: 'encrypt') The algorithm keyword
              to pass to ``polynomial_constr``.

            - ``**kwargs`` -- Keyword arguments to pass to
              ``polynomial_constr``. Keyword arguments will vary depending
              on ``polynomial_constr``.

            OUTPUT:

            - The output of ``polynomial_constr(row, col, algorithm,
              ** attr_dict)``. This is required to be a polynomial over
              `\GF{2^8}`.

            EXAMPLES::
                sage: from sage.crypto.mq.rijndael_gf import \
                ....: RijndaelGF
                sage: rgf = RijndaelGF(4, 4)
                sage: rcpc = RijndaelGF.Round_Component_Poly_Constr(
                ....: rgf._shift_rows_pc, rgf, "Shift Rows")
                sage: rcpc(1, 2)
                a13
                sage: all([rcpc(i, j) == rgf._shift_rows_pc(i, j)
                ....: for i in range(4) for j in range(4)])
                True
            """
            if row not in range(4):
                raise ValueError("keyword 'row' must be in range 0 - 3")
            if col not in range(self._Nb):
                msg = "keyword 'col' must be in range 0 - {0}"
                raise ValueError(msg.format(self._Nb-1))
            if algorithm not in ['encrypt', 'decrypt']:
                msg = ("keyword 'algorithm' must be either 'encrypt' or "
                       "'decrypt'")
                print(algorithm)
                raise ValueError(msg)
            return self._polynomial_constr(row, col, algorithm, **kwargs)

        def __repr__(self):
            r"""
            Returns a string representation of this object.

            EXAMPLES::

                sage: from sage.crypto.mq.rijndael_gf import \
                ....: RijndaelGF
                sage: rgf = RijndaelGF(4, 4)
                sage: RijndaelGF.Round_Component_Poly_Constr(
                ....: rgf._shift_rows_pc, rgf, "Shift Rows")
                A polynomial constructor for the function 'Shift Rows' of Rijndael-GF block cipher with block length 4, key length 4, and 10 rounds.
                sage: RijndaelGF.Round_Component_Poly_Constr(
                ....: rgf._shift_rows_pc, rgf)
                A polynomial constructor of a round component of Rijndael-GF block cipher with block length 4, key length 4, and 10 rounds.
            """
            if self._rc_name is None:
                msg = "A polynomial constructor of a round component of {0}"
                return msg.format(self._rgf_name)
            else:
                msg = "A polynomial constructor for the function '{0}' of {1}"
                return msg.format(self._rc_name, self._rgf_name)
