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