text: /**********************************************************************
   * Copyright (c) 2013, 2014 Pieter Wuille                             *
   * Distributed under the MIT software license, see the accompanying   *
   * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
   **********************************************************************/
  
  #ifndef _SECP256K1_ECKEY_IMPL_H_
  #define _SECP256K1_ECKEY_IMPL_H_
  
  #include "eckey.h"
  
  #include "scalar.h"
  #include "field.h"
  #include "group.h"
  #include "ecmult_gen.h"
  
  static int secp256k1_eckey_pubkey_parse(secp256k1_ge_t *elem, const unsigned char *pub, int size) {
      if (size == 33 && (pub[0] == 0x02 || pub[0] == 0x03)) {
          secp256k1_fe_t x;
          return secp256k1_fe_set_b32(&x, pub+1) && secp256k1_ge_set_xo(elem, &x, pub[0] == 0x03);
      } else if (size == 65 && (pub[0] == 0x04 || pub[0] == 0x06 || pub[0] == 0x07)) {
          secp256k1_fe_t x, y;
          if (!secp256k1_fe_set_b32(&x, pub+1) || !secp256k1_fe_set_b32(&y, pub+33)) {
              return 0;
          }
          secp256k1_ge_set_xy(elem, &x, &y);
          if ((pub[0] == 0x06 || pub[0] == 0x07) && secp256k1_fe_is_odd(&y) != (pub[0] == 0x07))
              return 0;
          return secp256k1_ge_is_valid(elem);
      } else {
          return 0;
      }
  }
  
  static int secp256k1_eckey_pubkey_serialize(secp256k1_ge_t *elem, unsigned char *pub, int *size, int compressed) {
      if (secp256k1_ge_is_infinity(elem)) {
          return 0;
      }
      secp256k1_fe_normalize(&elem->x);
      secp256k1_fe_normalize(&elem->y);
      secp256k1_fe_get_b32(&pub[1], &elem->x);
      if (compressed) {
          *size = 33;
          pub[0] = 0x02 | (secp256k1_fe_is_odd(&elem->y) ? 0x01 : 0x00);
      } else {
          *size = 65;
          pub[0] = 0x04;
          secp256k1_fe_get_b32(&pub[33], &elem->y);
      }
      return 1;
  }
  
  static int secp256k1_eckey_privkey_parse(secp256k1_scalar_t *key, const unsigned char *privkey, int privkeylen) {
      const unsigned char *end = privkey + privkeylen;
      /* sequence header */
      if (end < privkey+1 || *privkey != 0x30)
          return 0;
      privkey++;
      /* sequence length constructor */
      int lenb = 0;
      if (end < privkey+1 || !(*privkey & 0x80))
          return 0;
      lenb = *privkey & ~0x80; privkey++;
      if (lenb < 1 || lenb > 2)
          return 0;
      if (end < privkey+lenb)
          return 0;
      /* sequence length */
      int len = 0;
      len = privkey[lenb-1] | (lenb > 1 ? privkey[lenb-2] << 8 : 0);
      privkey += lenb;
      if (end < privkey+len)
          return 0;
      /* sequence element 0: version number (=1) */
      if (end < privkey+3 || privkey[0] != 0x02 || privkey[1] != 0x01 || privkey[2] != 0x01)
          return 0;
      privkey += 3;
      /* sequence element 1: octet string, up to 32 bytes */
      if (end < privkey+2 || privkey[0] != 0x04 || privkey[1] > 0x20 || end < privkey+2+privkey[1])
          return 0;
      int overflow = 0;
      unsigned char c[32] = {0};
      memcpy(c + 32 - privkey[1], privkey + 2, privkey[1]);
      secp256k1_scalar_set_b32(key, c, &overflow);
      memset(c, 0, 32);
      return !overflow;
  }
  
  static int secp256k1_eckey_privkey_serialize(unsigned char *privkey, int *privkeylen, const secp256k1_scalar_t *key, int compressed) {
      secp256k1_gej_t rp;
      secp256k1_ecmult_gen(&rp, key);
      secp256k1_ge_t r;
      secp256k1_ge_set_gej(&r, &rp);
      if (compressed) {
          static const unsigned char begin[] = {
              0x30,0x81,0xD3,0x02,0x01,0x01,0x04,0x20
          };
          static const unsigned char middle[] = {
              0xA0,0x81,0x85,0x30,0x81,0x82,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
              0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
              0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
              0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
              0x21,0x02,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
              0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
              0x17,0x98,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
              0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
              0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x24,0x03,0x22,0x00
          };
          unsigned char *ptr = privkey;
          memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
          secp256k1_scalar_get_b32(ptr, key); ptr += 32;
          memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
          int pubkeylen = 0;
          if (!secp256k1_eckey_pubkey_serialize(&r, ptr, &pubkeylen, 1)) {
              return 0;
          }
          ptr += pubkeylen;
          *privkeylen = ptr - privkey;
      } else {
          static const unsigned char begin[] = {
              0x30,0x82,0x01,0x13,0x02,0x01,0x01,0x04,0x20
          };
          static const unsigned char middle[] = {
              0xA0,0x81,0xA5,0x30,0x81,0xA2,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
              0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
              0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
              0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
              0x41,0x04,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
              0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
              0x17,0x98,0x48,0x3A,0xDA,0x77,0x26,0xA3,0xC4,0x65,0x5D,0xA4,0xFB,0xFC,0x0E,0x11,
              0x08,0xA8,0xFD,0x17,0xB4,0x48,0xA6,0x85,0x54,0x19,0x9C,0x47,0xD0,0x8F,0xFB,0x10,
              0xD4,0xB8,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
              0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
              0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x44,0x03,0x42,0x00
          };
          unsigned char *ptr = privkey;
          memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
          secp256k1_scalar_get_b32(ptr, key); ptr += 32;
          memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
          int pubkeylen = 0;
          if (!secp256k1_eckey_pubkey_serialize(&r, ptr, &pubkeylen, 0)) {
              return 0;
          }
          ptr += pubkeylen;
          *privkeylen = ptr - privkey;
      }
      return 1;
  }
  
  static int secp256k1_eckey_privkey_tweak_add(secp256k1_scalar_t *key, const secp256k1_scalar_t *tweak) {
      secp256k1_scalar_add(key, key, tweak);
      if (secp256k1_scalar_is_zero(key))
          return 0;
      return 1;
  }
  
  static int secp256k1_eckey_pubkey_tweak_add(secp256k1_ge_t *key, const secp256k1_scalar_t *tweak) {
      secp256k1_gej_t pt;
      secp256k1_gej_set_ge(&pt, key);
      secp256k1_scalar_t one;
      secp256k1_scalar_set_int(&one, 1);
      secp256k1_ecmult(&pt, &pt, &one, tweak);
  
      if (secp256k1_gej_is_infinity(&pt))
          return 0;
      secp256k1_ge_set_gej(key, &pt);
      return 1;
  }
  
  static int secp256k1_eckey_privkey_tweak_mul(secp256k1_scalar_t *key, const secp256k1_scalar_t *tweak) {
      if (secp256k1_scalar_is_zero(tweak))
          return 0;
  
      secp256k1_scalar_mul(key, key, tweak);
      return 1;
  }
  
  static int secp256k1_eckey_pubkey_tweak_mul(secp256k1_ge_t *key, const secp256k1_scalar_t *tweak) {
      if (secp256k1_scalar_is_zero(tweak))
          return 0;
  
      secp256k1_scalar_t zero;
      secp256k1_scalar_set_int(&zero, 0);
      secp256k1_gej_t pt;
      secp256k1_gej_set_ge(&pt, key);
      secp256k1_ecmult(&pt, &pt, tweak, &zero);
      secp256k1_ge_set_gej(key, &pt);
      return 1;
  }
  
  #endif
  