/* This file is part of GNUnet (C) 2013 Christian Grothoff (and other contributing authors) GNUnet is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, 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 General Public License for more details. You should have received a copy of the GNU General Public License along with GNUnet; see the file COPYING. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ /** * @file include/gnunet_secretsharing_service.h * @brief verifiable additive secret sharing and cooperative decryption * @author Florian Dold */ #ifndef GNUNET_SECRETSHARING_SERVICE_H #define GNUNET_SECRETSHARING_SERVICE_H #ifdef __cplusplus extern "C" { #if 0 /* keep Emacsens' auto-indent happy */ } #endif #endif #include "platform.h" #include "gnunet_common.h" #include "gnunet_time_lib.h" #include "gnunet_configuration_lib.h" #include /** * 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, 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 his 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 his 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