summaryrefslogtreecommitdiff
path: root/src/include/gnunet_secretsharing_service.h
blob: 127f1db7813aa72c4e511b1984f4c629a787edce (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
/*
      This file is part of GNUnet
      Copyright (C) 2013 GNUnet e.V.

      GNUnet is free software: you can redistribute it and/or modify it
      under the terms of the GNU Affero General Public License as published
      by the Free Software Foundation, either version 3 of the License,
      or (at your option) any later version.

      GNUnet is distributed in the hope that it will be useful, but
      WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      Affero General Public License for more details.

      You should have received a copy of the GNU Affero General Public License
      along with this program.  If not, see <http://www.gnu.org/licenses/>.

     SPDX-License-Identifier: AGPL3.0-or-later
 */

/**
 * @author Florian Dold
 *
 * @file
 * Verifiable additive secret sharing and cooperative decryption
 *
 * @defgroup secretsharing  Secret Sharing service
 * Verifiable additive secret sharing and cooperative decryption.
 * @{
 */

#ifndef GNUNET_SECRETSHARING_SERVICE_H
#define GNUNET_SECRETSHARING_SERVICE_H

#ifdef __cplusplus
extern "C"
{
#if 0                           /* keep Emacsens' auto-indent happy */
}
#endif
#endif

#include "gnunet_common.h"
#include "gnunet_time_lib.h"
#include "gnunet_configuration_lib.h"
#include <gcrypt.h>


/**
 * Number of bits for secretsharing elements.
 * Must be smaller than the Pallier key size used internally
 * by the secretsharing service.
 * When changing this value, other internal parameters must also
 * be adjusted.
 */
#define GNUNET_SECRETSHARING_ELGAMAL_BITS 1024


/**
 * The q-parameter for ElGamal encryption, a 1024-bit safe prime.
 */
#define GNUNET_SECRETSHARING_ELGAMAL_P_HEX  \
  "0x08a347d3d69e8b2dd7d1b12a08dfbccbebf4ca" \
  "6f4269a0814e158a34312964d946b3ef22882317" \
  "2bcf30fc08f772774cb404f9bc002a6f66b09a79" \
  "d810d67c4f8cb3bedc6060e3c8ef874b1b64df71" \
  "6c7d2b002da880e269438d5a776e6b5f253c8df5" \
  "6a16b1c7ce58def07c03db48238aadfc52a354a2" \
  "7ed285b0c1675cad3f3"

/**
 * The q-parameter for ElGamal encryption,
 * a 1023-bit Sophie Germain prime, q = (p-1)/2
 */
#define GNUNET_SECRETSHARING_ELGAMAL_Q_HEX  \
  "0x0451a3e9eb4f4596ebe8d895046fde65f5fa65" \
  "37a134d040a70ac51a1894b26ca359f79144118b" \
  "95e7987e047bb93ba65a027cde001537b3584d3c" \
  "ec086b3e27c659df6e303071e477c3a58db26fb8" \
  "b63e958016d4407134a1c6ad3bb735af929e46fa" \
  "b50b58e3e72c6f783e01eda411c556fe2951aa51" \
  "3f6942d860b3ae569f9"

/**
 * The g-parameter for ElGamal encryption,
 * a generator of the unique size q subgroup of Z_p^*
 */
#define GNUNET_SECRETSHARING_ELGAMAL_G_HEX  \
  "0x05c00c36d2e822950087ef09d8252994adc4e4" \
  "8fe3ec70269f035b46063aff0c99b633fd64df43" \
  "02442e1914c829a41505a275438871f365e91c12" \
  "3d5303ef9e90f4b8cb89bf86cc9b513e74a72634" \
  "9cfd9f953674fab5d511e1c078fc72d72b34086f" \
  "c82b4b951989eb85325cb203ff98df76bc366bba" \
  "1d7024c3650f60d0da"


/**
 * Session that will eventually establish a shared secred between
 * the involved peers and allow encryption and cooperative decryption.
 */
struct GNUNET_SECRETSHARING_Session;

/**
 * Share of a secret shared with a group of peers.
 * Contains the secret share itself, the public key, the list of peers, and the
 * exponential commitments to the secret shares of the other peers.
 */
struct GNUNET_SECRETSHARING_Share;


/**
 * Handle to cancel a cooperative decryption operation.
 */
struct GNUNET_SECRETSHARING_DecryptionHandle;


/**
 * Public key of a group sharing a secret.
 */
struct GNUNET_SECRETSHARING_PublicKey
{
  uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof(uint32_t)];
};


/**
 * Encrypted field element.
 */
struct GNUNET_SECRETSHARING_Ciphertext
{
  uint32_t c1_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof(uint32_t)];
  uint32_t c2_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof(uint32_t)];
};


/**
 * Plain, unencrypted message that can be encrypted with
 * a group public key.
 * Note that we are not operating in GF(2^n), thus not every
 * bit pattern is a valid plain text.
 */
struct GNUNET_SECRETSHARING_Plaintext
{
  /**
   * Value of the message.
   */
  uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof(uint32_t)];
};


/**
 * Called once the secret has been established with all peers, or the deadline is due.
 *
 * Note that the number of peers can be smaller than 'k' (this threshold parameter), which
 * makes the threshold crypto system useless.  However, in this case one can still determine which peers
 * were able to participate in the secret sharing successfully.
 *
 * If the secret sharing failed, num_ready_peers is 0 and my_share and public_key is NULL.
 *
 * After this callback has been called, the secretsharing session will be invalid.
 *
 * @param cls closure
 * @param my_share the share of this peer
 * @param public_key public key of the session
 * @param num_ready_peers number of peers in @a ready_peers
 * @param ready_peers peers that successfuly participated in establishing
 *                    the shared secret
 */
typedef void
(*GNUNET_SECRETSHARING_SecretReadyCallback) (void *cls,
                                             struct GNUNET_SECRETSHARING_Share *
                                             my_share,
                                             struct
                                             GNUNET_SECRETSHARING_PublicKey *
                                             public_key,
                                             unsigned int num_ready_peers,
                                             const struct
                                             GNUNET_PeerIdentity *ready_peers);


/**
 * Called when a decryption has succeeded.
 *
 * @param cls closure
 * @param data decrypted value
 * @param data_size number of bytes in @a data
 */
typedef void
(*GNUNET_SECRETSHARING_DecryptCallback) (void *cls,
                                         const struct
                                         GNUNET_SECRETSHARING_Plaintext *
                                         plaintext);


/**
 * Create a session that will eventually establish a shared secret
 * with the other peers.
 *
 * @param cfg configuration to use
 * @param num_peers number of peers in @a peers
 * @param peers array of peers that we will share secrets with, can optionally contain the local peer
 * @param session_id unique session id
 * @param start When should all peers be available for sharing the secret?
 *              Random number generation can take place before the start time.
 * @param deadline point in time where the session must be established; taken as hint
 *                 by underlying consensus sessions
 * @param threshold minimum number of peers that must cooperate to decrypt a value
 * @param cb called when the secret has been established
 * @param cls closure for @a cb
 */
struct GNUNET_SECRETSHARING_Session *
GNUNET_SECRETSHARING_create_session (const struct
                                     GNUNET_CONFIGURATION_Handle *cfg,
                                     unsigned int num_peers,
                                     const struct GNUNET_PeerIdentity *peers,
                                     const struct GNUNET_HashCode *session_id,
                                     struct GNUNET_TIME_Absolute start,
                                     struct GNUNET_TIME_Absolute deadline,
                                     unsigned int threshold,
                                     GNUNET_SECRETSHARING_SecretReadyCallback cb,
                                     void *cls);


/**
 * Destroy a secret sharing session.
 * The secret ready callback will not be called.
 *
 * @param s session to destroy
 */
void
GNUNET_SECRETSHARING_session_destroy (struct GNUNET_SECRETSHARING_Session *s);


/**
 * Encrypt a value.  This operation is executed locally, no communication is
 * necessary.
 *
 * This is a helper function, encryption can be done soley with a session's public key
 * and the crypto system parameters.
 *
 * @param public_key public key to use for decryption
 * @param message message to encrypt
 * @param message_size number of bytes in @a message
 * @param result_ciphertext pointer to store the resulting ciphertext
 * @return #GNUNET_YES on succes, #GNUNET_SYSERR if the message is invalid (invalid range)
 */
int
GNUNET_SECRETSHARING_encrypt (const struct
                              GNUNET_SECRETSHARING_PublicKey *public_key,
                              const struct
                              GNUNET_SECRETSHARING_Plaintext *plaintext,
                              struct GNUNET_SECRETSHARING_Ciphertext *
                              result_ciphertext);


/**
 * Publish the given ciphertext for decryption.  Once a sufficient (>=k) number of peers has
 * published the same value, it will be decrypted.
 *
 * When the operation is canceled, the decrypt_cb is not called anymore, but the calling
 * peer may already have irrevocably contributed its share for the decryption of the value.
 *
 * @param cfg configuration to use
 * @param share our secret share to use for decryption
 * @param ciphertext ciphertext to publish in order to decrypt it (if enough peers agree)
 * @param decrypt_cb callback called once the decryption succeeded
 * @param start By when should the cooperation for decryption start?
 * @param deadline By when should the decryption be finished?
 * @param decrypt_cb_cls closure for @a decrypt_cb
 * @return handle to cancel the operation
 */
struct GNUNET_SECRETSHARING_DecryptionHandle *
GNUNET_SECRETSHARING_decrypt (const struct GNUNET_CONFIGURATION_Handle *cfg,
                              struct GNUNET_SECRETSHARING_Share *share,
                              const struct
                              GNUNET_SECRETSHARING_Ciphertext *ciphertext,
                              struct GNUNET_TIME_Absolute start,
                              struct GNUNET_TIME_Absolute deadline,
                              GNUNET_SECRETSHARING_DecryptCallback decrypt_cb,
                              void *decrypt_cb_cls);


/**
 * Cancel a decryption.
 *
 * The decrypt_cb is not called anymore, but the calling
 * peer may already have irrevocably contributed its share for the decryption of the value.
 *
 * @param dh to cancel
 */
void
GNUNET_SECRETSHARING_decrypt_cancel (struct
                                     GNUNET_SECRETSHARING_DecryptionHandle *dh);


/**
 * Read a share from its binary representation.
 *
 * @param data Binary representation of the share.
 * @param len Length of @a data.
 * @param[out] readlen Number of bytes read,
 *             ignored if NULL.
 * @return The share, or NULL on error.
 */
struct GNUNET_SECRETSHARING_Share *
GNUNET_SECRETSHARING_share_read (const void *data, size_t len, size_t *readlen);


/**
 * Convert a share to its binary representation.
 * Can be called with a NULL @a buf to get the size of the share.
 *
 * @param share Share to write.
 * @param buf Buffer to write to.
 * @param buflen Number of writable bytes in @a buf.
 * @param[out] writelen Pointer to store number of bytes written,
 *             ignored if NULL.
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure.
 */
int
GNUNET_SECRETSHARING_share_write (const struct
                                  GNUNET_SECRETSHARING_Share *share,
                                  void *buf, size_t buflen, size_t *writelen);


void
GNUNET_SECRETSHARING_share_destroy (struct GNUNET_SECRETSHARING_Share *share);


int
GNUNET_SECRETSHARING_plaintext_generate (struct
                                         GNUNET_SECRETSHARING_Plaintext *
                                         plaintext,
                                         gcry_mpi_t exponent);

int
GNUNET_SECRETSHARING_plaintext_generate_i (struct
                                           GNUNET_SECRETSHARING_Plaintext *
                                           plaintext,
                                           int64_t exponent);


#if 0                           /* keep Emacsens' auto-indent happy */
{
#endif
#ifdef __cplusplus
}
#endif

#endif

/** @} */  /* end of group */