2 This file is part of GNUnet
3 Copyright (C) 2013 GNUnet e.V.
5 GNUnet is free software: you can redistribute it and/or modify it
6 under the terms of the GNU Affero General Public License as published
7 by the Free Software Foundation, either version 3 of the License,
8 or (at your option) any later version.
10 GNUnet is distributed in the hope that it will be useful, but
11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Affero General Public License for more details.
15 You should have received a copy of the GNU Affero General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
20 * @author Florian Dold
23 * Verifiable additive secret sharing and cooperative decryption
25 * @defgroup secretsharing Secret Sharing service
26 * Verifiable additive secret sharing and cooperative decryption.
30 #ifndef GNUNET_SECRETSHARING_SERVICE_H
31 #define GNUNET_SECRETSHARING_SERVICE_H
36 #if 0 /* keep Emacsens' auto-indent happy */
41 #include "gnunet_common.h"
42 #include "gnunet_time_lib.h"
43 #include "gnunet_configuration_lib.h"
48 * Number of bits for secretsharing elements.
49 * Must be smaller than the Pallier key size used internally
50 * by the secretsharing service.
51 * When changing this value, other internal parameters must also
54 #define GNUNET_SECRETSHARING_ELGAMAL_BITS 1024
58 * The q-parameter for ElGamal encryption, a 1024-bit safe prime.
60 #define GNUNET_SECRETSHARING_ELGAMAL_P_HEX \
61 "0x08a347d3d69e8b2dd7d1b12a08dfbccbebf4ca" \
62 "6f4269a0814e158a34312964d946b3ef22882317" \
63 "2bcf30fc08f772774cb404f9bc002a6f66b09a79" \
64 "d810d67c4f8cb3bedc6060e3c8ef874b1b64df71" \
65 "6c7d2b002da880e269438d5a776e6b5f253c8df5" \
66 "6a16b1c7ce58def07c03db48238aadfc52a354a2" \
70 * The q-parameter for ElGamal encryption,
71 * a 1023-bit Sophie Germain prime, q = (p-1)/2
73 #define GNUNET_SECRETSHARING_ELGAMAL_Q_HEX \
74 "0x0451a3e9eb4f4596ebe8d895046fde65f5fa65" \
75 "37a134d040a70ac51a1894b26ca359f79144118b" \
76 "95e7987e047bb93ba65a027cde001537b3584d3c" \
77 "ec086b3e27c659df6e303071e477c3a58db26fb8" \
78 "b63e958016d4407134a1c6ad3bb735af929e46fa" \
79 "b50b58e3e72c6f783e01eda411c556fe2951aa51" \
83 * The g-parameter for ElGamal encryption,
84 * a generator of the unique size q subgroup of Z_p^*
86 #define GNUNET_SECRETSHARING_ELGAMAL_G_HEX \
87 "0x05c00c36d2e822950087ef09d8252994adc4e4" \
88 "8fe3ec70269f035b46063aff0c99b633fd64df43" \
89 "02442e1914c829a41505a275438871f365e91c12" \
90 "3d5303ef9e90f4b8cb89bf86cc9b513e74a72634" \
91 "9cfd9f953674fab5d511e1c078fc72d72b34086f" \
92 "c82b4b951989eb85325cb203ff98df76bc366bba" \
98 * Session that will eventually establish a shared secred between
99 * the involved peers and allow encryption and cooperative decryption.
101 struct GNUNET_SECRETSHARING_Session;
104 * Share of a secret shared with a group of peers.
105 * Contains the secret share itself, the public key, the list of peers, and the
106 * exponential commitments to the secret shares of the other peers.
108 struct GNUNET_SECRETSHARING_Share;
112 * Handle to cancel a cooperative decryption operation.
114 struct GNUNET_SECRETSHARING_DecryptionHandle;
118 * Public key of a group sharing a secret.
120 struct GNUNET_SECRETSHARING_PublicKey
122 uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
127 * Encrypted field element.
129 struct GNUNET_SECRETSHARING_Ciphertext
131 uint32_t c1_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
132 uint32_t c2_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
137 * Plain, unencrypted message that can be encrypted with
138 * a group public key.
139 * Note that we are not operating in GF(2^n), thus not every
140 * bit pattern is a valid plain text.
142 struct GNUNET_SECRETSHARING_Plaintext
145 * Value of the message.
147 uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
152 * Called once the secret has been established with all peers, or the deadline is due.
154 * Note that the number of peers can be smaller than 'k' (this threshold parameter), which
155 * makes the threshold crypto system useless. However, in this case one can still determine which peers
156 * were able to participate in the secret sharing successfully.
158 * If the secret sharing failed, num_ready_peers is 0 and my_share and public_key is NULL.
160 * After this callback has been called, the secretsharing session will be invalid.
163 * @param my_share the share of this peer
164 * @param public_key public key of the session
165 * @param num_ready_peers number of peers in @a ready_peers
166 * @param ready_peers peers that successfuly participated in establishing
170 (*GNUNET_SECRETSHARING_SecretReadyCallback) (void *cls,
171 struct GNUNET_SECRETSHARING_Share *my_share,
172 struct GNUNET_SECRETSHARING_PublicKey *public_key,
173 unsigned int num_ready_peers,
174 const struct GNUNET_PeerIdentity *ready_peers);
178 * Called when a decryption has succeeded.
181 * @param data decrypted value
182 * @param data_size number of bytes in @a data
185 (*GNUNET_SECRETSHARING_DecryptCallback) (void *cls,
186 const struct GNUNET_SECRETSHARING_Plaintext *plaintext);
190 * Create a session that will eventually establish a shared secret
191 * with the other peers.
193 * @param cfg configuration to use
194 * @param num_peers number of peers in @a peers
195 * @param peers array of peers that we will share secrets with, can optionally contain the local peer
196 * @param session_id unique session id
197 * @param start When should all peers be available for sharing the secret?
198 * Random number generation can take place before the start time.
199 * @param deadline point in time where the session must be established; taken as hint
200 * by underlying consensus sessions
201 * @param threshold minimum number of peers that must cooperate to decrypt a value
202 * @param cb called when the secret has been established
203 * @param cls closure for @a cb
205 struct GNUNET_SECRETSHARING_Session *
206 GNUNET_SECRETSHARING_create_session (const struct GNUNET_CONFIGURATION_Handle *cfg,
207 unsigned int num_peers,
208 const struct GNUNET_PeerIdentity *peers,
209 const struct GNUNET_HashCode *session_id,
210 struct GNUNET_TIME_Absolute start,
211 struct GNUNET_TIME_Absolute deadline,
212 unsigned int threshold,
213 GNUNET_SECRETSHARING_SecretReadyCallback cb,
218 * Destroy a secret sharing session.
219 * The secret ready callback will not be called.
221 * @param s session to destroy
224 GNUNET_SECRETSHARING_session_destroy (struct GNUNET_SECRETSHARING_Session *s);
228 * Encrypt a value. This operation is executed locally, no communication is
231 * This is a helper function, encryption can be done soley with a session's public key
232 * and the crypto system parameters.
234 * @param public_key public key to use for decryption
235 * @param message message to encrypt
236 * @param message_size number of bytes in @a message
237 * @param result_ciphertext pointer to store the resulting ciphertext
238 * @return #GNUNET_YES on succes, #GNUNET_SYSERR if the message is invalid (invalid range)
241 GNUNET_SECRETSHARING_encrypt (const struct GNUNET_SECRETSHARING_PublicKey *public_key,
242 const struct GNUNET_SECRETSHARING_Plaintext *plaintext,
243 struct GNUNET_SECRETSHARING_Ciphertext *result_ciphertext);
247 * Publish the given ciphertext for decryption. Once a sufficient (>=k) number of peers has
248 * published the same value, it will be decrypted.
250 * When the operation is canceled, the decrypt_cb is not called anymore, but the calling
251 * peer may already have irrevocably contributed his share for the decryption of the value.
253 * @param cfg configuration to use
254 * @param share our secret share to use for decryption
255 * @param ciphertext ciphertext to publish in order to decrypt it (if enough peers agree)
256 * @param decrypt_cb callback called once the decryption succeeded
257 * @param start By when should the cooperation for decryption start?
258 * @param deadline By when should the decryption be finished?
259 * @param decrypt_cb_cls closure for @a decrypt_cb
260 * @return handle to cancel the operation
262 struct GNUNET_SECRETSHARING_DecryptionHandle *
263 GNUNET_SECRETSHARING_decrypt (const struct GNUNET_CONFIGURATION_Handle *cfg,
264 struct GNUNET_SECRETSHARING_Share *share,
265 const struct GNUNET_SECRETSHARING_Ciphertext *ciphertext,
266 struct GNUNET_TIME_Absolute start,
267 struct GNUNET_TIME_Absolute deadline,
268 GNUNET_SECRETSHARING_DecryptCallback decrypt_cb,
269 void *decrypt_cb_cls);
273 * Cancel a decryption.
275 * The decrypt_cb is not called anymore, but the calling
276 * peer may already have irrevocably contributed his share for the decryption of the value.
278 * @param dh to cancel
281 GNUNET_SECRETSHARING_decrypt_cancel (struct GNUNET_SECRETSHARING_DecryptionHandle *dh);
285 * Read a share from its binary representation.
287 * @param data Binary representation of the share.
288 * @param len Length of @a data.
289 * @param[out] readlen Number of bytes read,
291 * @return The share, or NULL on error.
293 struct GNUNET_SECRETSHARING_Share *
294 GNUNET_SECRETSHARING_share_read (const void *data, size_t len, size_t *readlen);
298 * Convert a share to its binary representation.
299 * Can be called with a NULL @a buf to get the size of the share.
301 * @param share Share to write.
302 * @param buf Buffer to write to.
303 * @param buflen Number of writable bytes in @a buf.
304 * @param[out] writelen Pointer to store number of bytes written,
306 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure.
309 GNUNET_SECRETSHARING_share_write (const struct GNUNET_SECRETSHARING_Share *share,
310 void *buf, size_t buflen, size_t *writelen);
314 GNUNET_SECRETSHARING_share_destroy (struct GNUNET_SECRETSHARING_Share *share);
318 GNUNET_SECRETSHARING_plaintext_generate (struct GNUNET_SECRETSHARING_Plaintext *plaintext,
319 gcry_mpi_t exponent);
322 GNUNET_SECRETSHARING_plaintext_generate_i (struct GNUNET_SECRETSHARING_Plaintext *plaintext,
326 #if 0 /* keep Emacsens' auto-indent happy */
335 /** @} */ /* end of group */