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22 * @author Florian Dold
25 * Verifiable additive secret sharing and cooperative decryption
27 * @defgroup secretsharing Secret Sharing service
28 * Verifiable additive secret sharing and cooperative decryption.
32 #ifndef GNUNET_SECRETSHARING_SERVICE_H
33 #define GNUNET_SECRETSHARING_SERVICE_H
38 #if 0 /* keep Emacsens' auto-indent happy */
43 #include "gnunet_common.h"
44 #include "gnunet_time_lib.h"
45 #include "gnunet_configuration_lib.h"
50 * Number of bits for secretsharing elements.
51 * Must be smaller than the Pallier key size used internally
52 * by the secretsharing service.
53 * When changing this value, other internal parameters must also
56 #define GNUNET_SECRETSHARING_ELGAMAL_BITS 1024
60 * The q-parameter for ElGamal encryption, a 1024-bit safe prime.
62 #define GNUNET_SECRETSHARING_ELGAMAL_P_HEX \
63 "0x08a347d3d69e8b2dd7d1b12a08dfbccbebf4ca" \
64 "6f4269a0814e158a34312964d946b3ef22882317" \
65 "2bcf30fc08f772774cb404f9bc002a6f66b09a79" \
66 "d810d67c4f8cb3bedc6060e3c8ef874b1b64df71" \
67 "6c7d2b002da880e269438d5a776e6b5f253c8df5" \
68 "6a16b1c7ce58def07c03db48238aadfc52a354a2" \
72 * The q-parameter for ElGamal encryption,
73 * a 1023-bit Sophie Germain prime, q = (p-1)/2
75 #define GNUNET_SECRETSHARING_ELGAMAL_Q_HEX \
76 "0x0451a3e9eb4f4596ebe8d895046fde65f5fa65" \
77 "37a134d040a70ac51a1894b26ca359f79144118b" \
78 "95e7987e047bb93ba65a027cde001537b3584d3c" \
79 "ec086b3e27c659df6e303071e477c3a58db26fb8" \
80 "b63e958016d4407134a1c6ad3bb735af929e46fa" \
81 "b50b58e3e72c6f783e01eda411c556fe2951aa51" \
85 * The g-parameter for ElGamal encryption,
86 * a generator of the unique size q subgroup of Z_p^*
88 #define GNUNET_SECRETSHARING_ELGAMAL_G_HEX \
89 "0x05c00c36d2e822950087ef09d8252994adc4e4" \
90 "8fe3ec70269f035b46063aff0c99b633fd64df43" \
91 "02442e1914c829a41505a275438871f365e91c12" \
92 "3d5303ef9e90f4b8cb89bf86cc9b513e74a72634" \
93 "9cfd9f953674fab5d511e1c078fc72d72b34086f" \
94 "c82b4b951989eb85325cb203ff98df76bc366bba" \
100 * Session that will eventually establish a shared secred between
101 * the involved peers and allow encryption and cooperative decryption.
103 struct GNUNET_SECRETSHARING_Session;
106 * Share of a secret shared with a group of peers.
107 * Contains the secret share itself, the public key, the list of peers, and the
108 * exponential commitments to the secret shares of the other peers.
110 struct GNUNET_SECRETSHARING_Share;
114 * Handle to cancel a cooperative decryption operation.
116 struct GNUNET_SECRETSHARING_DecryptionHandle;
120 * Public key of a group sharing a secret.
122 struct GNUNET_SECRETSHARING_PublicKey
124 uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
129 * Encrypted field element.
131 struct GNUNET_SECRETSHARING_Ciphertext
133 uint32_t c1_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
134 uint32_t c2_bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
139 * Plain, unencrypted message that can be encrypted with
140 * a group public key.
141 * Note that we are not operating in GF(2^n), thus not every
142 * bit pattern is a valid plain text.
144 struct GNUNET_SECRETSHARING_Plaintext
147 * Value of the message.
149 uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
154 * Called once the secret has been established with all peers, or the deadline is due.
156 * Note that the number of peers can be smaller than 'k' (this threshold parameter), which
157 * makes the threshold crypto system useless. However, in this case one can still determine which peers
158 * were able to participate in the secret sharing successfully.
160 * If the secret sharing failed, num_ready_peers is 0 and my_share and public_key is NULL.
162 * After this callback has been called, the secretsharing session will be invalid.
165 * @param my_share the share of this peer
166 * @param public_key public key of the session
167 * @param num_ready_peers number of peers in @a ready_peers
168 * @param ready_peers peers that successfuly participated in establishing
172 (*GNUNET_SECRETSHARING_SecretReadyCallback) (void *cls,
173 struct GNUNET_SECRETSHARING_Share *my_share,
174 struct GNUNET_SECRETSHARING_PublicKey *public_key,
175 unsigned int num_ready_peers,
176 const struct GNUNET_PeerIdentity *ready_peers);
180 * Called when a decryption has succeeded.
183 * @param data decrypted value
184 * @param data_size number of bytes in @a data
187 (*GNUNET_SECRETSHARING_DecryptCallback) (void *cls,
188 const struct GNUNET_SECRETSHARING_Plaintext *plaintext);
192 * Create a session that will eventually establish a shared secret
193 * with the other peers.
195 * @param cfg configuration to use
196 * @param num_peers number of peers in @a peers
197 * @param peers array of peers that we will share secrets with, can optionally contain the local peer
198 * @param session_id unique session id
199 * @param start When should all peers be available for sharing the secret?
200 * Random number generation can take place before the start time.
201 * @param deadline point in time where the session must be established; taken as hint
202 * by underlying consensus sessions
203 * @param threshold minimum number of peers that must cooperate to decrypt a value
204 * @param cb called when the secret has been established
205 * @param cls closure for @a cb
207 struct GNUNET_SECRETSHARING_Session *
208 GNUNET_SECRETSHARING_create_session (const struct GNUNET_CONFIGURATION_Handle *cfg,
209 unsigned int num_peers,
210 const struct GNUNET_PeerIdentity *peers,
211 const struct GNUNET_HashCode *session_id,
212 struct GNUNET_TIME_Absolute start,
213 struct GNUNET_TIME_Absolute deadline,
214 unsigned int threshold,
215 GNUNET_SECRETSHARING_SecretReadyCallback cb,
220 * Destroy a secret sharing session.
221 * The secret ready callback will not be called.
223 * @param s session to destroy
226 GNUNET_SECRETSHARING_session_destroy (struct GNUNET_SECRETSHARING_Session *s);
230 * Encrypt a value. This operation is executed locally, no communication is
233 * This is a helper function, encryption can be done soley with a session's public key
234 * and the crypto system parameters.
236 * @param public_key public key to use for decryption
237 * @param message message to encrypt
238 * @param message_size number of bytes in @a message
239 * @param result_ciphertext pointer to store the resulting ciphertext
240 * @return #GNUNET_YES on succes, #GNUNET_SYSERR if the message is invalid (invalid range)
243 GNUNET_SECRETSHARING_encrypt (const struct GNUNET_SECRETSHARING_PublicKey *public_key,
244 const struct GNUNET_SECRETSHARING_Plaintext *plaintext,
245 struct GNUNET_SECRETSHARING_Ciphertext *result_ciphertext);
249 * Publish the given ciphertext for decryption. Once a sufficient (>=k) number of peers has
250 * published the same value, it will be decrypted.
252 * When the operation is canceled, the decrypt_cb is not called anymore, but the calling
253 * peer may already have irrevocably contributed his share for the decryption of the value.
255 * @param cfg configuration to use
256 * @param share our secret share to use for decryption
257 * @param ciphertext ciphertext to publish in order to decrypt it (if enough peers agree)
258 * @param decrypt_cb callback called once the decryption succeeded
259 * @param start By when should the cooperation for decryption start?
260 * @param deadline By when should the decryption be finished?
261 * @param decrypt_cb_cls closure for @a decrypt_cb
262 * @return handle to cancel the operation
264 struct GNUNET_SECRETSHARING_DecryptionHandle *
265 GNUNET_SECRETSHARING_decrypt (const struct GNUNET_CONFIGURATION_Handle *cfg,
266 struct GNUNET_SECRETSHARING_Share *share,
267 const struct GNUNET_SECRETSHARING_Ciphertext *ciphertext,
268 struct GNUNET_TIME_Absolute start,
269 struct GNUNET_TIME_Absolute deadline,
270 GNUNET_SECRETSHARING_DecryptCallback decrypt_cb,
271 void *decrypt_cb_cls);
275 * Cancel a decryption.
277 * The decrypt_cb is not called anymore, but the calling
278 * peer may already have irrevocably contributed his share for the decryption of the value.
280 * @param dh to cancel
283 GNUNET_SECRETSHARING_decrypt_cancel (struct GNUNET_SECRETSHARING_DecryptionHandle *dh);
287 * Read a share from its binary representation.
289 * @param data Binary representation of the share.
290 * @param len Length of @a data.
291 * @param[out] readlen Number of bytes read,
293 * @return The share, or NULL on error.
295 struct GNUNET_SECRETSHARING_Share *
296 GNUNET_SECRETSHARING_share_read (const void *data, size_t len, size_t *readlen);
300 * Convert a share to its binary representation.
301 * Can be called with a NULL @a buf to get the size of the share.
303 * @param share Share to write.
304 * @param buf Buffer to write to.
305 * @param buflen Number of writable bytes in @a buf.
306 * @param[out] writelen Pointer to store number of bytes written,
308 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure.
311 GNUNET_SECRETSHARING_share_write (const struct GNUNET_SECRETSHARING_Share *share,
312 void *buf, size_t buflen, size_t *writelen);
316 GNUNET_SECRETSHARING_share_destroy (struct GNUNET_SECRETSHARING_Share *share);
320 GNUNET_SECRETSHARING_plaintext_generate (struct GNUNET_SECRETSHARING_Plaintext *plaintext,
321 gcry_mpi_t exponent);
324 GNUNET_SECRETSHARING_plaintext_generate_i (struct GNUNET_SECRETSHARING_Plaintext *plaintext,
328 #if 0 /* keep Emacsens' auto-indent happy */
337 /** @} */ /* end of group */