2 This file is part of GNUnet
3 Copyright (C) 2013 Christian Grothoff (and other contributing authors)
5 GNUnet is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published
7 by the Free Software Foundation; either version 3, or (at your
8 option) any later version.
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11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with GNUnet; see the file COPYING. If not, write to the
17 Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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22 * @file include/gnunet_secretsharing_service.h
23 * @brief verifiable additive secret sharing and cooperative decryption
24 * @author Florian Dold
27 #ifndef GNUNET_SECRETSHARING_SERVICE_H
28 #define GNUNET_SECRETSHARING_SERVICE_H
33 #if 0 /* keep Emacsens' auto-indent happy */
39 #include "gnunet_common.h"
40 #include "gnunet_time_lib.h"
41 #include "gnunet_configuration_lib.h"
46 * Number of bits for secretsharing elements.
47 * Must be smaller than the Pallier key size used internally
48 * by the secretsharing service.
49 * When changing this value, other internal parameters must also
52 #define GNUNET_SECRETSHARING_ELGAMAL_BITS 1024
56 * The q-parameter for ElGamal encryption, a 1024-bit safe prime.
58 #define GNUNET_SECRETSHARING_ELGAMAL_P_HEX \
59 "0x08a347d3d69e8b2dd7d1b12a08dfbccbebf4ca" \
60 "6f4269a0814e158a34312964d946b3ef22882317" \
61 "2bcf30fc08f772774cb404f9bc002a6f66b09a79" \
62 "d810d67c4f8cb3bedc6060e3c8ef874b1b64df71" \
63 "6c7d2b002da880e269438d5a776e6b5f253c8df5" \
64 "6a16b1c7ce58def07c03db48238aadfc52a354a2" \
68 * The q-parameter for ElGamal encryption,
69 * a 1023-bit Sophie Germain prime, q = (p-1)/2
71 #define GNUNET_SECRETSHARING_ELGAMAL_Q_HEX \
72 "0x0451a3e9eb4f4596ebe8d895046fde65f5fa65" \
73 "37a134d040a70ac51a1894b26ca359f79144118b" \
74 "95e7987e047bb93ba65a027cde001537b3584d3c" \
75 "ec086b3e27c659df6e303071e477c3a58db26fb8" \
76 "b63e958016d4407134a1c6ad3bb735af929e46fa" \
77 "b50b58e3e72c6f783e01eda411c556fe2951aa51" \
81 * The g-parameter for ElGamal encryption,
82 * a generator of the unique size q subgroup of Z_p^*
84 #define GNUNET_SECRETSHARING_ELGAMAL_G_HEX \
85 "0x05c00c36d2e822950087ef09d8252994adc4e4" \
86 "8fe3ec70269f035b46063aff0c99b633fd64df43" \
87 "02442e1914c829a41505a275438871f365e91c12" \
88 "3d5303ef9e90f4b8cb89bf86cc9b513e74a72634" \
89 "9cfd9f953674fab5d511e1c078fc72d72b34086f" \
90 "c82b4b951989eb85325cb203ff98df76bc366bba" \
96 * Session that will eventually establish a shared secred between
97 * the involved peers and allow encryption and cooperative decryption.
99 struct GNUNET_SECRETSHARING_Session;
102 * Share of a secret shared with a group of peers.
103 * Contains the secret share itself, the public key, the list of peers, and the
104 * exponential commitments to the secret shares of the other peers.
106 struct GNUNET_SECRETSHARING_Share;
110 * Handle to cancel a cooperative decryption operation.
112 struct GNUNET_SECRETSHARING_DecryptionHandle;
116 * Public key of a group sharing a secret.
118 struct GNUNET_SECRETSHARING_PublicKey
120 uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
125 * Encrypted field element.
127 struct GNUNET_SECRETSHARING_Ciphertext
129 uint32_t c1_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
130 uint32_t c2_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
135 * Plain, unencrypted message that can be encrypted with
136 * a group public key.
137 * Note that we are not operating in GF(2^n), thus not every
138 * bit pattern is a valid plain text.
140 struct GNUNET_SECRETSHARING_Plaintext
143 * Value of the message.
145 uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
150 * Called once the secret has been established with all peers, or the deadline is due.
152 * Note that the number of peers can be smaller than 'k' (this threshold parameter), which
153 * makes the threshold crypto system useless. However, in this case one can still determine which peers
154 * were able to participate in the secret sharing successfully.
156 * If the secret sharing failed, num_ready_peers is 0 and my_share and public_key is NULL.
158 * After this callback has been called, the secretsharing session will be invalid.
161 * @param my_share the share of this peer
162 * @param public_key public key of the session
163 * @param num_ready_peers number of peers in @a ready_peers
164 * @param ready_peers peers that successfuly participated in establishing
167 typedef void (*GNUNET_SECRETSHARING_SecretReadyCallback) (void *cls,
168 struct GNUNET_SECRETSHARING_Share *my_share,
169 struct GNUNET_SECRETSHARING_PublicKey *public_key,
170 unsigned int num_ready_peers,
171 struct GNUNET_PeerIdentity *ready_peers);
175 * Called when a decryption has succeeded.
178 * @param data decrypted value
179 * @param data_size number of bytes in @a data
181 typedef void (*GNUNET_SECRETSHARING_DecryptCallback) (void *cls,
182 const struct GNUNET_SECRETSHARING_Plaintext *plaintext);
186 * Create a session that will eventually establish a shared secret
187 * with the other peers.
189 * @param cfg configuration to use
190 * @param num_peers number of peers in @a peers
191 * @param peers array of peers that we will share secrets with, can optionally contain the local peer
192 * @param session_id unique session id
193 * @param start When should all peers be available for sharing the secret?
194 * Random number generation can take place before the start time.
195 * @param deadline point in time where the session must be established; taken as hint
196 * by underlying consensus sessions
197 * @param threshold minimum number of peers that must cooperate to decrypt a value
198 * @param cb called when the secret has been established
199 * @param cls closure for @a cb
201 struct GNUNET_SECRETSHARING_Session *
202 GNUNET_SECRETSHARING_create_session (const struct GNUNET_CONFIGURATION_Handle *cfg,
203 unsigned int num_peers,
204 const struct GNUNET_PeerIdentity *peers,
205 const struct GNUNET_HashCode *session_id,
206 struct GNUNET_TIME_Absolute start,
207 struct GNUNET_TIME_Absolute deadline,
208 unsigned int threshold,
209 GNUNET_SECRETSHARING_SecretReadyCallback cb,
214 * Destroy a secret sharing session.
215 * The secret ready callback will not be called.
217 * @param s session to destroy
220 GNUNET_SECRETSHARING_session_destroy (struct GNUNET_SECRETSHARING_Session *s);
224 * Encrypt a value. This operation is executed locally, no communication is
227 * This is a helper function, encryption can be done soley with a session's public key
228 * and the crypto system parameters.
230 * @param public_key public key to use for decryption
231 * @param message message to encrypt
232 * @param message_size number of bytes in @a message
233 * @param result_ciphertext pointer to store the resulting ciphertext
234 * @return #GNUNET_YES on succes, #GNUNET_SYSERR if the message is invalid (invalid range)
237 GNUNET_SECRETSHARING_encrypt (const struct GNUNET_SECRETSHARING_PublicKey *public_key,
238 const struct GNUNET_SECRETSHARING_Plaintext *plaintext,
239 struct GNUNET_SECRETSHARING_Ciphertext *result_ciphertext);
243 * Publish the given ciphertext for decryption. Once a sufficient (>=k) number of peers has
244 * published the same value, it will be decrypted.
246 * When the operation is canceled, the decrypt_cb is not called anymore, but the calling
247 * peer may already have irrevocably contributed his share for the decryption of the value.
249 * @param cfg configuration to use
250 * @param share our secret share to use for decryption
251 * @param ciphertext ciphertext to publish in order to decrypt it (if enough peers agree)
252 * @param decrypt_cb callback called once the decryption succeeded
253 * @param start By when should the cooperation for decryption start?
254 * @param deadline By when should the decryption be finished?
255 * @param decrypt_cb_cls closure for @a decrypt_cb
256 * @return handle to cancel the operation
258 struct GNUNET_SECRETSHARING_DecryptionHandle *
259 GNUNET_SECRETSHARING_decrypt (const struct GNUNET_CONFIGURATION_Handle *cfg,
260 struct GNUNET_SECRETSHARING_Share *share,
261 const struct GNUNET_SECRETSHARING_Ciphertext *ciphertext,
262 struct GNUNET_TIME_Absolute start,
263 struct GNUNET_TIME_Absolute deadline,
264 GNUNET_SECRETSHARING_DecryptCallback decrypt_cb,
265 void *decrypt_cb_cls);
269 * Cancel a decryption.
271 * The decrypt_cb is not called anymore, but the calling
272 * peer may already have irrevocably contributed his share for the decryption of the value.
274 * @param dh to cancel
277 GNUNET_SECRETSHARING_decrypt_cancel (struct GNUNET_SECRETSHARING_DecryptionHandle *dh);
281 * Read a share from its binary representation.
283 * @param data Binary representation of the share.
284 * @param len Length of @a data.
285 * @param[out] readlen Number of bytes read,
287 * @return The share, or NULL on error.
289 struct GNUNET_SECRETSHARING_Share *
290 GNUNET_SECRETSHARING_share_read (const void *data, size_t len, size_t *readlen);
294 * Convert a share to its binary representation.
295 * Can be called with a NULL @a buf to get the size of the share.
297 * @param share Share to write.
298 * @param buf Buffer to write to.
299 * @param buflen Number of writable bytes in @a buf.
300 * @param[out] writelen Pointer to store number of bytes written,
302 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure.
305 GNUNET_SECRETSHARING_share_write (const struct GNUNET_SECRETSHARING_Share *share,
306 void *buf, size_t buflen, size_t *writelen);
310 GNUNET_SECRETSHARING_share_destroy (struct GNUNET_SECRETSHARING_Share *share);
314 GNUNET_SECRETSHARING_plaintext_generate (struct GNUNET_SECRETSHARING_Plaintext *plaintext,
315 gcry_mpi_t exponent);
318 GNUNET_SECRETSHARING_plaintext_generate_i (struct GNUNET_SECRETSHARING_Plaintext *plaintext,
324 #if 0 /* keep Emacsens' auto-indent happy */