/*
This file is part of GNUnet
- (C) 2013 Christian Grothoff (and other contributing authors)
+ Copyright (C) 2013 GNUnet e.V.
GNUnet is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
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.
+ Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ Boston, MA 02110-1301, USA.
*/
/**
- * @file include/gnunet_secretsharing_service.h
- * @brief verified additive secret sharing and cooperative decryption
* @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
#endif
#endif
-#include "platform.h"
#include "gnunet_common.h"
#include "gnunet_time_lib.h"
#include "gnunet_configuration_lib.h"
#include <gcrypt.h>
+/**
+ * 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.
/**
- * Parameters of the crypto system.
+ * Public key of a group sharing a secret.
*/
-struct GNUNET_SECRETSHARING_Parameters
+struct GNUNET_SECRETSHARING_PublicKey
{
- /**
- * Threshold, that is, minimum number of peers that
- * must cooperate to decrypt a value.
- */
- unsigned int k;
- /**
- * Prime with p = 2q+1.
- */
- gcry_mpi_t p;
- /**
- * Prime.
- */
- gcry_mpi_t q;
- /**
- * Generator of G_q.
- */
- gcry_mpi_t g;
+ uint32_t bits[GNUNET_SECRETSHARING_ELGAMAL_BITS / 8 / sizeof (uint32_t)];
};
/**
* Encrypted field element.
*/
-struct GNUNET_SECRETSHARING_Ciphertext
+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
{
/**
- * First component.
- */
- gcry_mpi_t c1;
- /**
- * Second component.
+ * Value of the message.
*/
- gcry_mpi_t c2;
+ 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 that 'k' (this threshold parameter), which
- * makes the threshold crypto system useledd. However, in this case one can still determine which peers
+ * 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 @ready_peers
- * @parem ready_peers peers that successfuly participated in establishing
+ * @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,
- gcry_mpi_t public_key,
- unsigned int num_ready_peers,
- const struct GNUNET_PeerIdentity *ready_peers);
+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 result decrypted value
+ * @param data decrypted value
+ * @param data_size number of bytes in @a data
*/
-typedef void (*GNUNET_SECRETSHARING_DecryptCallback) (void *cls,
- gcry_mpi_t result);
+typedef void
+(*GNUNET_SECRETSHARING_DecryptCallback) (void *cls,
+ const struct GNUNET_SECRETSHARING_Plaintext *plaintext);
/**
* with the other peers.
*
* @param cfg configuration to use
- * @param num_peers number of peers in @peers
+ * @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 cb
+ * @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,
- struct GNUNET_SECRETSHARING_Parameters *parameters,
- GNUNET_SECRETSHARING_SecretReadyCallback *cb,
+ unsigned int threshold,
+ GNUNET_SECRETSHARING_SecretReadyCallback cb,
void *cls);
/**
* Destroy a secret sharing session.
+ * The secret ready callback will not be called.
*
- * @param session session to destroy
+ * @param s session to destroy
*/
void
-GNUNET_SECRETSHARING_destroy_session (struct GNUNET_SECRETSHARING_Session *session);
+GNUNET_SECRETSHARING_session_destroy (struct GNUNET_SECRETSHARING_Session *s);
/**
* This is a helper function, encryption can be done soley with a session's public key
* and the crypto system parameters.
*
- * @param session session to take the key for encryption from,
- * the session's ready callback must have been already called
+ * @param public_key public key to use for decryption
* @param message message to encrypt
- * @param result_cyphertext pointer to store the resulting ciphertext
- * @return GNUNET_YES on succes, GNUNET_SYSERR if the message is invalid (invalid range)
+ * @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_Session *session,
- gcry_mpi_t message,
+int
+GNUNET_SECRETSHARING_encrypt (const struct GNUNET_SECRETSHARING_PublicKey *public_key,
+ const struct GNUNET_SECRETSHARING_Plaintext *plaintext,
struct GNUNET_SECRETSHARING_Ciphertext *result_ciphertext);
* 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 session session to use for the decryption
+ * @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 cls closure for decrypt_cb
+ * @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_publish_decrypt (struct GNUNET_SECRETSHARING_Session *session,
- struct GNUNET_SECRETSHARING_Ciphertext *ciphertext,
- GNUNET_SECRETSHARING_DecryptCallback decrypt_cb,
- void *cls);
+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 decryption_handle decryption to cancel
+ * @param dh to cancel
*/
void
-GNUNET_SECRETSHARING_cancel_decrypt (struct GNUNET_SECRETSHARING_DecryptionHandle *decryption_handle);
+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
#endif
+
+/** @} */ /* end of group */
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