github.com/ethereum/go-ethereum@v1.16.1/crypto/secp256k1/libsecp256k1/src/modules/ecdh/main_impl.h (about)

     1  /***********************************************************************
     2   * Copyright (c) 2015 Andrew Poelstra                                  *
     3   * Distributed under the MIT software license, see the accompanying    *
     4   * file COPYING or https://www.opensource.org/licenses/mit-license.php.*
     5   ***********************************************************************/
     6  
     7  #ifndef SECP256K1_MODULE_ECDH_MAIN_H
     8  #define SECP256K1_MODULE_ECDH_MAIN_H
     9  
    10  #include "../../../include/secp256k1_ecdh.h"
    11  #include "../../ecmult_const_impl.h"
    12  
    13  static int ecdh_hash_function_sha256(unsigned char *output, const unsigned char *x32, const unsigned char *y32, void *data) {
    14      unsigned char version = (y32[31] & 0x01) | 0x02;
    15      secp256k1_sha256 sha;
    16      (void)data;
    17  
    18      secp256k1_sha256_initialize(&sha);
    19      secp256k1_sha256_write(&sha, &version, 1);
    20      secp256k1_sha256_write(&sha, x32, 32);
    21      secp256k1_sha256_finalize(&sha, output);
    22      secp256k1_sha256_clear(&sha);
    23  
    24      return 1;
    25  }
    26  
    27  const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256 = ecdh_hash_function_sha256;
    28  const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default = ecdh_hash_function_sha256;
    29  
    30  int secp256k1_ecdh(const secp256k1_context* ctx, unsigned char *output, const secp256k1_pubkey *point, const unsigned char *scalar, secp256k1_ecdh_hash_function hashfp, void *data) {
    31      int ret = 0;
    32      int overflow = 0;
    33      secp256k1_gej res;
    34      secp256k1_ge pt;
    35      secp256k1_scalar s;
    36      unsigned char x[32];
    37      unsigned char y[32];
    38  
    39      VERIFY_CHECK(ctx != NULL);
    40      ARG_CHECK(output != NULL);
    41      ARG_CHECK(point != NULL);
    42      ARG_CHECK(scalar != NULL);
    43  
    44      if (hashfp == NULL) {
    45          hashfp = secp256k1_ecdh_hash_function_default;
    46      }
    47  
    48      secp256k1_pubkey_load(ctx, &pt, point);
    49      secp256k1_scalar_set_b32(&s, scalar, &overflow);
    50  
    51      overflow |= secp256k1_scalar_is_zero(&s);
    52      secp256k1_scalar_cmov(&s, &secp256k1_scalar_one, overflow);
    53  
    54      secp256k1_ecmult_const(&res, &pt, &s);
    55      secp256k1_ge_set_gej(&pt, &res);
    56  
    57      /* Compute a hash of the point */
    58      secp256k1_fe_normalize(&pt.x);
    59      secp256k1_fe_normalize(&pt.y);
    60      secp256k1_fe_get_b32(x, &pt.x);
    61      secp256k1_fe_get_b32(y, &pt.y);
    62  
    63      ret = hashfp(output, x, y, data);
    64  
    65      secp256k1_memclear(x, sizeof(x));
    66      secp256k1_memclear(y, sizeof(y));
    67      secp256k1_scalar_clear(&s);
    68      secp256k1_ge_clear(&pt);
    69      secp256k1_gej_clear(&res);
    70  
    71      return !!ret & !overflow;
    72  }
    73  
    74  #endif /* SECP256K1_MODULE_ECDH_MAIN_H */