frosix

Multiparty signature service (experimental)
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keygen_begin.c (3601B)

      1 /*
      2   This file is part of Frosix
      3   Copyright (C) 2022, 2023 Joel Urech
      4 
      5   Frosix is free software; you can redistribute it and/or modify it under the
      6   terms of the GNU Affero General Public License as published by the Free Software
      7   Foundation; either version 3, or (at your option) any later version.
      8 
      9   Frosix is distributed in the hope that it will be useful, but WITHOUT ANY
     10   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
     11   A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more details.
     12 
     13   You should have received a copy of the GNU Affero General Public License along with
     14   Frosix; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
     15 */
     16 /**
     17  * @file keygen_begin.c
     18  * @brief Implementation of the first round of the distributed key generation
     19  * @author Joel Urech
     20 */
     21 #include "keygen.h"
     22 #include "keygen_common.h"
     23 
     24 
     25 enum GNUNET_GenericReturnValue
     26 FROST_keygen_begin (struct FROST_DkgCommitment *dkg_commitment,
     27                     struct FROST_DkgShare dkg_shares[],
     28                     const struct FROST_DkgContextString *context_string,
     29                     const struct FROST_HashCode *additional_data,
     30                     uint8_t my_index,
     31                     uint8_t num_of_participants,
     32                     uint8_t threshold)
     33 {
     34   /* check params */
     35   if (GNUNET_OK != FROST_validate_dkg_params (my_index,
     36                                               threshold,
     37                                               num_of_participants))
     38     return GNUNET_NO;
     39 
     40   /* check if calling function misbehaves */
     41   GNUNET_assert (NULL != dkg_commitment);
     42   GNUNET_assert (NULL != dkg_shares);
     43   GNUNET_assert (NULL != context_string);
     44 
     45   /* derive secret value 'x0' from context_string */
     46   struct FROST_DkgSecretKey secret;
     47   FROST_kdf_scalar_to_curve (&secret.sk,
     48                              0,
     49                              &context_string->con_str);
     50 
     51   /* Generate commitments and shares */
     52   FROST_generate_shares_ (dkg_shares,
     53                           dkg_commitment,
     54                           &secret,
     55                           &context_string->con_str,
     56                           num_of_participants,
     57                           threshold);
     58 
     59   /* Generate the signature / zero knowledge proof of secret 'x0' */
     60 
     61   // hash secret value and map back to a scalar -> our 'rnd'-value
     62   struct FROST_HashState r_h_state;
     63   FROST_hash_init (&r_h_state);
     64   FROST_hash_scalar_update (&r_h_state,
     65                             &secret.sk);
     66   FROST_hash_fixed_update (&r_h_state,
     67                            "FROST-DKG-ZKP",
     68                            strlen ("FROST-DKG-ZKP"));
     69   struct FROST_HashCode r_h;
     70   FROST_hash_final (&r_h_state,
     71                     &r_h);
     72 
     73   struct FROST_Scalar r;
     74   FROST_hash_to_scalar (&r,
     75                         &r_h);
     76 
     77   // compute signature / zkp
     78   FROST_base_mul_scalar (&dkg_commitment->zkp.r,
     79                          &r);
     80 
     81   struct FROST_DkgShareCommitment s_pub;
     82   FROST_base_mul_scalar (&s_pub.sc,
     83                          &secret.sk);
     84 
     85   struct FROST_DkgChallenge challenge;
     86   FROST_generate_dkg_challenge_ (&challenge,
     87                                  my_index,
     88                                  &s_pub,
     89                                  &dkg_commitment->zkp,
     90                                  additional_data);
     91 
     92   FROST_scalar_mul_scalar (&dkg_commitment->zkp.z,
     93                            &secret.sk,
     94                            &challenge.c);
     95   FROST_scalar_add_scalar (&dkg_commitment->zkp.z,
     96                            &dkg_commitment->zkp.z,
     97                            &r);
     98 
     99   return GNUNET_OK;
    100 }