\input texinfo @c -*-texinfo-*-
@comment %**start of header
@setfilename mit-scheme-blowfish.info
@include version.texi
@set SCMVERS 11.1
@settitle MIT/GNU Scheme Blowfish Plugin Manual
@comment %**end of header

@copying
This manual documents MIT/GNU Scheme Blowfish @value{VERSION}.

Copyright @copyright{} 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993,
    1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004,
    2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015,
    2016, 2017, 2018, 2019, 2020 Massachusetts Institute of Technology

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts and no Back-Cover Texts.
A copy of the license is included in the section entitled ``GNU Free
Documentation License.''
@end quotation
@end copying

@dircategory Programming Languages
@direntry
* MIT/GNU Scheme Blowfish: (mit-scheme-blowfish).
                                Blowfish plugin.
@end direntry

@titlepage
@title MIT/GNU Scheme Blowfish Plugin Manual
@subtitle a Blowfish block cipher plugin (version @value{VERSION})
@subtitle for MIT/GNU Scheme version @value{SCMVERS}
@subtitle @value{UPDATED}
@author by Matt Birkholz
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@ifnottex
@node Top
@top Blowfish Plugin Manual

@insertcopying
@end ifnottex

@menu
* Introduction::
* Procedures::
* DES Modes::
* GNU Free Documentation License::
@end menu

@node Introduction
@chapter Introduction

This plugin is a dynamically loadable wrapper of the Blowfish block
cipher C API as implemented by libssl (OpenSSL).

The cipher operates on 64 bit (8 byte) blocks of data and uses a
variable size key.  Keys with 128 bits (16 bytes) are considered good
for modest encryption.  Blowfish can be used in the same modes as DES,
is quite a bit faster than DES, and much faster than IDEA or RC2.

The plugin includes a Scheme procedure to feed bytes from a binary
input port to the library, and write the encrypted bytes to a binary
output port.

@node Procedures
@chapter Procedures

Blowfish consists of a key setup phase and the actual encryption or
decryption phase.

@deffn Procedure blowfish-set-key bytes
Generate a Blowfish key from @var{bytes}, which must be 72 bytes or
less in length.  For text keys (strings), apply @code{md5-string}
and use the digest for @var{bytes}.
@end deffn

@deffn Procedure blowfish-ecb input output key encyrpt?
Apply Blowfish in Electronic Code Book mode.
@var{Input} is an 8-byte byte vector.
@var{Output} is an 8-byte byte vector.
@var{Key} is a Blowfish key.
@var{Encrypt?} specifies whether to encrypt (when @code{#t}) or decrypt
(when @code{#f}).
@end deffn

The mode functions below all operate on variable length data.  They
all take an initialization vector which needs to be passed along into
the next call of the same function for the same message.  The vector
may be initialized with anything, but the recipient needs to know what
it was initialized with, or it won't be able to decrypt.  Some
programs and protocols simplify this, like SSH, where the vector is
simply initialized to zero.  @code{Blowfish-cbc} operates on data that
is a multiple of 8 bytes long, while @code{blowfish-cfb64} and
@code{blowfish-ofb64} are used to encrypt any number of bytes.  The
purpose of the latter two is to simulate stream ciphers, and
therefore, they have a parameter @code{num}, the current offset in the
initialization vector, which should start at zero and be stored
between calls.

@deffn Procedure blowfish-cbc input output key init encrypt?
Apply Blowfish in Cipher Block Chaining mode.
@var{Input} is a multiple of 8 bytes.
@var{Output} is the same number of bytes as in Input.
@var{Key} is a Blowfish key.
@var{Init} is an 8 byte initialization vector;
  it is modified after each call.
  The value from any call may be passed in to a later call.
@var{Encrypt?} specifies whether to encrypt (when @code{#t}) or decrypt
(when @code{#f}).
@end deffn

@deffn Procedure blowfish-cfb64 input istart iend output ostart key init num encrypt?
Apply Blowfish in Cipher Feed-Back mode.
@var{Istart} and @var{Iend} specify a range of bytes in @var{Input}.
@var{Ostart} specifies the first byte to write in @var{Output}.
@var{Key} is a Blowfish key.
@var{Init} is an 8 byte initialization vector;
  it is modified after each call.
  The value from any call may be passed in to a later call.
  The initial value must be unique for each message/key pair.
@var{Num} is an integer from 0 to 7 inclusive, the low 3 bits of the
  number of bytes that have previously been processed in this stream.
@var{Encrypt?} specifies whether to encrypt (when @code{#t}) or decrypt
(when @code{#f}).
The returned value is the new value of Num.
@end deffn

@deffn Procedure blowfish-ofb64 input istart iend output ostart key init num
Apply Blowfish in Output Feed-Back mode.
@var{Istart} and @var{Iend} specify a range of bytes in @var{Input}.
@var{Ostart} specifies the first byte to write in @var{Output}.
@var{Key} is a Blowfish key.
@var{Init} is an 8 byte initialization vector;
  it is modified after each call.
  The value from any call may be passed in to a later call.
  The initial value must be unique for each message/key pair.
@var{Num} is an integer from 0 to 7 inclusive, the low 3 bits of the
  number of bytes that have previously been processed in this stream.
The returned value is the new value of Num.
@end deffn

Two convenience procedures are also provided.

@deffn Procedure blowfish-encrypt-port input output key init encrypt?
Reads bytes from @var{input}, which should be in blocking mode, until
the end.  Feeds the bytes to @code{blowfish-cfb64} and writes the
resulting, encrypted bytes to @var{output}.  @var{Key} and
@var{init} are passed to @code{blowfish-cfb64} (which modifies
the latter).
@var{Encrypt?} specifies whether to encrypt (when @code{#t}) or decrypt
(when @code{#f}).
@end deffn

@deffn Procedure compute-blowfish-init-vector
Returns a new initialization vector that includes a timestamp with a
resolution of milliseconds, plus 20 random bits.  This should make it
very likely unique.
@end deffn

The Blowfish cipher was invented and described by Counterpane (see
@url{http://www.counterpane.com/blowfish.html}).  Most of this manual
was adapted from the OpenSSL manual pages.

@node DES Modes
@chapter DES Modes

This chapter was written in large parts by Eric Young in his original
documentation for SSLeay, the predecessor of OpenSSL.  In turn, he
attributed it to:

@smallexample
AS 2805.5.2
Australian Standard
Electronic funds transfer - Requirements for interfaces,
Part 5.2: Modes of operation for an n-bit block cipher algorithm
Appendix A
@end smallexample

@section Electronic Codebook Mode (ECB)

64 bits are enciphered at a time.

The order of the blocks can be rearranged without detection.

The same plain text block always produces the same cipher text block
(for the same key) making it vulnerable to a dictionary attack.

An error will only affect one cipher text block.

@section Cipher Block Chaining Mode (CBC)

A multiple of 64 bits are enciphered at a time.

The CBC mode produces the same cipher text whenever the same plain text
is encrypted using the same key and starting variable.

The chaining operation makes the cipher text blocks dependent on the
current and all preceding plain text blocks and therefore blocks can
not be rearranged.

The use of different starting variables prevents the same plain text
enciphering to the same cipher text.

An error will affect the current and the following cipher text blocks.

@section Cipher Feedback Mode (CFB)

Any number of bits, j, up to 64, are enciphered at a time.

The CFB mode produces the same cipher text whenever the same plain text
is encrypted using the same key and starting variable.

The chaining operation makes the cipher text variables dependent on
the current and all preceding variables and therefore j-bit variables
are chained together and can not be rearranged.

The use of different starting variables prevents the same plain text
enciphering to the same cipher text.

The strength of the CFB mode depends on the size of k (maximal if j
= k).  In my implementation this is always the case.

Selection of a small value for j will require more cycles through the
encipherment algorithm per unit of plain text and thus cause greater
processing overheads.

Only multiples of j bits can be enciphered.

An error will affect the current and the following cipher text
variables.

@section Output Feedback Mode (OFB)

Any number of bits, j, up to 64, are enciphered at a time.

The OFB mode produces the same cipher text whenever the same plain text
enciphered using the same key and starting variable.  More over, in
the OFB mode the same key stream is produced when the same key and
start variable are used.  Consequently, for security reasons a
specific start variable should be used only once for a given key.

The absence of chaining makes the OFB more vulnerable to specific
attacks.

The use of different start variables values prevents the same
plain text enciphering to the same cipher text, by producing different
key streams.

Selection of a small value for j will require more cycles through the
encipherment algorithm per unit of plain text and thus cause greater
processing overheads.

Only multiples of j bits can be enciphered.

OFB mode of operation does not extend cipher text errors in the
resultant plain text output.  Every bit error in the cipher text causes
only one bit to be in error in the deciphered plain text.

OFB mode is not self-synchronizing.  If the two operations of
encipherment and decipherment get out of synchronism, the system
needs to be re-initialized.

Each re-initialization should use a value of the start variable
different from the start variable values used before with the same
key.  The reason for this is that an identical bit stream would be
produced each time from the same parameters.  This would be
susceptible to a 'known plain text' attack.

@node GNU Free Documentation License
@appendix GNU Free Documentation License

@cindex FDL, GNU Free Documentation License
@center Version 1.2, November 2002

@display
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@page
@appendixsec ADDENDUM: How to use this License for your documents

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@smallexample
@group
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@end smallexample

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@bye
