Botan: Botan::RTSS_Share Class Reference

Botan 1.10.17

Public Member Functions | Static Public Member Functions | List of all members
Botan::RTSS_Share Class Reference

`#include <tss.h>`

## Public Member Functions
bool | initialized () const
| RTSS_Share ()
| RTSS_Share (const std::string &hex_input)
byte | share_id () const
size_t | size () const
std::string | to_string () const

## Static Public Member Functions
static SecureVector< byte > | reconstruct (const std::vector< RTSS_Share > &shares)
static std::vector< RTSS_Share > | split (byte M, byte N, const byte secret[], u16bit secret_len, const byte identifier[16], RandomNumberGenerator &rng)

## Detailed Description

A split secret, using the format from draft-mcgrew-tss-03

Definition at line 21 of file tss.h.

## Constructor & Destructor Documentation

## ◆ RTSS_Share() [1/2]

Botan::RTSS_Share::RTSS_Share | ( |  | ) |
| inline

Definition at line 44 of file tss.h.

44 {}

## ◆ RTSS_Share() [2/2]

Botan::RTSS_Share::RTSS_Share | ( | const std::string & | hex_input | ) |

Parameters

  hex_input | the share encoded in hexadecimal

Definition at line 107 of file tss.cpp.

References Botan::hex_decode().

108 {
109 contents = hex_decode(hex_input);
110 }
Botan::hex_decode
size_t hex_decode(byte output[], const char input[], size_t input_length, size_t &input_consumed, bool ignore_ws)
Definition: hex.cpp:55

## Member Function Documentation

## ◆ initialized()

bool Botan::RTSS_Share::initialized | ( |  | ) | const
| inline

Returns
  if this TSS share was initialized or not

Definition at line 69 of file tss.h.

Referenced by share_id().

69 { return (contents.size() > 0); }
Botan::MemoryRegion::size
size_t size() const
Definition: secmem.h:29

## ◆ reconstruct()

SecureVector< byte > Botan::RTSS_Share::reconstruct | ( | const std::vector< RTSS_Share > & | shares | ) |
| static

Parameters

  shares | the list of shares

Definition at line 182 of file tss.cpp.

References Botan::make_u16bit(), Botan::same_mem(), share_id(), and size().

183 {
184 const size_t RTSS_HEADER_SIZE = 20;
185
186 for(size_t i = 0; i != shares.size(); ++i)
187 {
188 if(shares[i].size() != shares[0].size())
189 throw Decoding_Error("Different sized RTSS shares detected");
190 if(shares[i].share_id() == 0)
191 throw Decoding_Error("Invalid (id = 0) RTSS share detected");
192 if(shares[i].size() < RTSS_HEADER_SIZE)
193 throw Decoding_Error("Missing or malformed RTSS header");
194
195 if(!same_mem(&shares[0].contents[0],
196 &shares[i].contents[0], RTSS_HEADER_SIZE))
197 throw Decoding_Error("Different RTSS headers detected");
198 }
199
200 if(shares.size() < shares[0].contents[17])
201 throw Decoding_Error("Insufficient shares to do TSS reconstruction");
202
203 u16bit secret_len = make_u16bit(shares[0].contents[18],
204 shares[0].contents[19]);
205
206 byte hash_id = shares[0].contents[16];
207
208 std::auto_ptr<HashFunction> hash(get_rtss_hash_by_id(hash_id));
209
210 if(shares[0].size() != secret_len + hash->output_length() + RTSS_HEADER_SIZE + 1)
211 throw Decoding_Error("Bad RTSS length field in header");
212
213 std::vector<byte> V(shares.size());
214 SecureVector<byte> secret;
215
216 for(size_t i = RTSS_HEADER_SIZE + 1; i != shares[0].size(); ++i)
217 {
218 for(size_t j = 0; j != V.size(); ++j)
219 V[j] = shares[j].contents[i];
220
221 byte r = 0;
222 for(size_t k = 0; k != shares.size(); ++k)
223 {
224 // L_i function:
225 byte r2 = 1;
226 for(size_t l = 0; l != shares.size(); ++l)
227 {
228 if(k == l)
229 continue;
230
231 byte share_k = shares[k].share_id();
232 byte share_l = shares[l].share_id();
233
234 if(share_k == share_l)
235 throw Decoding_Error("Duplicate shares found in RTSS recovery");
236
237 byte div = RTSS_EXP[(255 +
238 RTSS_LOG[share_l] -
239 RTSS_LOG[share_k ^ share_l]) % 255];
240
241 r2 = gfp_mul(r2, div);
242 }
243
244 r ^= gfp_mul(V[k], r2);
245 }
246 secret.push_back(r);
247 }
248
249 if(secret.size() != secret_len + hash->output_length())
250 throw Decoding_Error("Bad length in RTSS output");
251
252 hash->update(&secret[0], secret_len);
253 SecureVector<byte> hash_check = hash->final();
254
255 if(!same_mem(&hash_check[0],
256 &secret[secret_len], hash->output_length()))
257 throw Decoding_Error("RTSS hash check failed");
258
259 return SecureVector<byte>(&secret[0], secret_len);
260 }
Botan::RTSS_Share::share_id
byte share_id() const
Definition: tss.cpp:112
Botan::same_mem
bool same_mem(const T *p1, const T *p2, size_t n)
Definition: mem_ops.h:57
Botan::byte
unsigned char byte
Definition: types.h:22
Botan::RTSS_Share::size
size_t size() const
Definition: tss.h:64
Botan::u16bit
unsigned short u16bit
Definition: types.h:27
Botan::make_u16bit
u16bit make_u16bit(byte i0, byte i1)
Definition: loadstor.h:47

## ◆ share_id()

byte Botan::RTSS_Share::share_id | ( |  | ) | const

Returns
  share identifier

Definition at line 112 of file tss.cpp.

References initialized().

Referenced by reconstruct().

113 {
114 if(!initialized())
115 throw Invalid_State("RTSS_Share::share_id not initialized");
116
117 return contents[20];
118 }
Botan::RTSS_Share::initialized
bool initialized() const
Definition: tss.h:69

## ◆ size()

size_t Botan::RTSS_Share::size | ( |  | ) | const
| inline

Returns
  size of this share in bytes

Definition at line 64 of file tss.h.

Referenced by reconstruct().

64 { return contents.size(); }
Botan::MemoryRegion::size
size_t size() const
Definition: secmem.h:29

## ◆ split()

std::vector< RTSS_Share > Botan::RTSS_Share::split | ( | byte | M,
|  | byte | N,
|  | const byte | secret[],
|  | u16bit | secret_len,
|  | const byte | identifier[16],
|  | RandomNumberGenerator & | rng
| ) |  |
| static

Parameters

  M | the number of shares needed to reconstruct
  N | the number of shares generated
  secret | the secret to split
  secret_len | the length of the secret
  identifier | the 16 byte share identifier
  rng | the random number generator to use

Definition at line 126 of file tss.cpp.

130 {
131 if(M == 0 || N == 0 || M > N)
132 throw Encoding_Error("RTSS_Share::split: M == 0 or N == 0 or M > N");
133
134 SHA_256 hash; // always use SHA-256 when generating shares
135
136 std::vector<RTSS_Share> shares(N);
137
138 // Create RTSS header in each share
139 for(byte i = 0; i != N; ++i)
140 {
141 shares[i].contents += std::make_pair(identifier, 16);
142 shares[i].contents += rtss_hash_id(hash.name());
143 shares[i].contents += M;
144 shares[i].contents += get_byte(0, S_len);
145 shares[i].contents += get_byte(1, S_len);
146 }
147
148 // Choose sequential values for X starting from 1
149 for(byte i = 0; i != N; ++i)
150 shares[i].contents.push_back(i+1);
151
152 // secret = S || H(S)
153 SecureVector<byte> secret(S, S_len);
154 secret += hash.process(S, S_len);
155
156 for(size_t i = 0; i != secret.size(); ++i)
157 {
158 std::vector<byte> coefficients(M-1);
159 rng.randomize(&coefficients[0], coefficients.size());
160
161 for(byte j = 0; j != N; ++j)
162 {
163 const byte X = j + 1;
164
165 byte sum = secret[i];
166 byte X_i = X;
167
168 for(size_t k = 0; k != coefficients.size(); ++k)
169 {
170 sum ^= gfp_mul(X_i, coefficients[k]);
171 X_i = gfp_mul(X_i, X);
172 }
173
174 shares[j].contents.push_back(sum);
175 }
176 }
177
178 return shares;
179 }
Botan::MemoryRegion::push_back
void push_back(T x)
Definition: secmem.h:149
Botan::get_byte
byte get_byte(size_t byte_num, T input)
Definition: get_byte.h:21
Botan::byte
unsigned char byte
Definition: types.h:22

## ◆ to_string()

std::string Botan::RTSS_Share::to_string | ( |  | ) | const

Returns
  hex representation

Definition at line 120 of file tss.cpp.

References Botan::hex_encode(), and Botan::MemoryRegion< T >::size().

121 {
122 return hex_encode(&contents[0], contents.size());
123 }
Botan::MemoryRegion::size
size_t size() const
Definition: secmem.h:29
Botan::hex_encode
void hex_encode(char output[], const byte input[], size_t input_length, bool uppercase)
Definition: hex.cpp:14

The documentation for this class was generated from the following files:

- src/constructs/tss/tss.h
- src/constructs/tss/tss.cpp