text: // Copyright (c) 2009-2019 Bitcoin Developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include "ecwrapper.h"
  
  #include "serialize.h"
  #include "uint256.h"
  
  #include <openssl/bn.h>
  #include <openssl/ecdsa.h>
  #include <openssl/obj_mac.h>
  
  namespace
  {
  /**
   * Perform ECDSA key recovery (see SEC1 4.1.6) for curves over (mod p)-fields
   * recid selects which key is recovered
   * if check is non-zero, additional checks are performed
   */
  int ECDSA_SIG_recover_key_GFp(EC_KEY* eckey, ECDSA_SIG* ecsig, const unsigned char* msg, int msglen, int recid, int check)
  {
      if (!eckey) return 0;
  
      int ret = 0;
      BN_CTX* ctx = NULL;
  
      BIGNUM* x = NULL;
      BIGNUM* e = NULL;
      BIGNUM* order = NULL;
      BIGNUM* sor = NULL;
      BIGNUM* eor = NULL;
      BIGNUM* field = NULL;
      EC_POINT* R = NULL;
      EC_POINT* O = NULL;
      EC_POINT* Q = NULL;
      BIGNUM* rr = NULL;
      BIGNUM* zero = NULL;
      int n = 0;
      int i = recid / 2;
  
      const EC_GROUP* group = EC_KEY_get0_group(eckey);
      if ((ctx = BN_CTX_new()) == NULL) {
          ret = -1;
          goto err;
      }
      BN_CTX_start(ctx);
      order = BN_CTX_get(ctx);
      if (!EC_GROUP_get_order(group, order, ctx)) {
          ret = -2;
          goto err;
      }
      x = BN_CTX_get(ctx);
      if (!BN_copy(x, order)) {
          ret = -1;
          goto err;
      }
      if (!BN_mul_word(x, i)) {
          ret = -1;
          goto err;
      }
      if (!BN_add(x, x, ecsig->r)) {
          ret = -1;
          goto err;
      }
      field = BN_CTX_get(ctx);
      if (!EC_GROUP_get_curve_GFp(group, field, NULL, NULL, ctx)) {
          ret = -2;
          goto err;
      }
      if (BN_cmp(x, field) >= 0) {
          ret = 0;
          goto err;
      }
      if ((R = EC_POINT_new(group)) == NULL) {
          ret = -2;
          goto err;
      }
      if (!EC_POINT_set_compressed_coordinates_GFp(group, R, x, recid % 2, ctx)) {
          ret = 0;
          goto err;
      }
      if (check) {
          if ((O = EC_POINT_new(group)) == NULL) {
              ret = -2;
              goto err;
          }
          if (!EC_POINT_mul(group, O, NULL, R, order, ctx)) {
              ret = -2;
              goto err;
          }
          if (!EC_POINT_is_at_infinity(group, O)) {
              ret = 0;
              goto err;
          }
      }
      if ((Q = EC_POINT_new(group)) == NULL) {
          ret = -2;
          goto err;
      }
      n = EC_GROUP_get_degree(group);
      e = BN_CTX_get(ctx);
      if (!BN_bin2bn(msg, msglen, e)) {
          ret = -1;
          goto err;
      }
      if (8 * msglen > n) BN_rshift(e, e, 8 - (n & 7));
      zero = BN_CTX_get(ctx);
      if (!BN_zero(zero)) {
          ret = -1;
          goto err;
      }
      if (!BN_mod_sub(e, zero, e, order, ctx)) {
          ret = -1;
          goto err;
      }
      rr = BN_CTX_get(ctx);
      if (!BN_mod_inverse(rr, ecsig->r, order, ctx)) {
          ret = -1;
          goto err;
      }
      sor = BN_CTX_get(ctx);
      if (!BN_mod_mul(sor, ecsig->s, rr, order, ctx)) {
          ret = -1;
          goto err;
      }
      eor = BN_CTX_get(ctx);
      if (!BN_mod_mul(eor, e, rr, order, ctx)) {
          ret = -1;
          goto err;
      }
      if (!EC_POINT_mul(group, Q, eor, R, sor, ctx)) {
          ret = -2;
          goto err;
      }
      if (!EC_KEY_set_public_key(eckey, Q)) {
          ret = -2;
          goto err;
      }
  
      ret = 1;
  
  err:
      if (ctx) {
          BN_CTX_end(ctx);
          BN_CTX_free(ctx);
      }
      if (R != NULL) EC_POINT_free(R);
      if (O != NULL) EC_POINT_free(O);
      if (Q != NULL) EC_POINT_free(Q);
      return ret;
  }
  
  } // anon namespace
  
  CECKey::CECKey()
  {
      pkey = EC_KEY_new_by_curve_name(NID_secp256k1);
      assert(pkey != NULL);
  }
  
  CECKey::~CECKey()
  {
      EC_KEY_free(pkey);
  }
  
  void CECKey::GetPubKey(std::vector<unsigned char>& pubkey, bool fCompressed)
  {
      EC_KEY_set_conv_form(pkey, fCompressed ? POINT_CONVERSION_COMPRESSED : POINT_CONVERSION_UNCOMPRESSED);
      int nSize = i2o_ECPublicKey(pkey, NULL);
      assert(nSize);
      assert(nSize <= 65);
      pubkey.clear();
      pubkey.resize(nSize);
      unsigned char* pbegin(begin_ptr(pubkey));
      int nSize2 = i2o_ECPublicKey(pkey, &pbegin);
      assert(nSize == nSize2);
  }
  
  bool CECKey::SetPubKey(const unsigned char* pubkey, size_t size)
  {
      return o2i_ECPublicKey(&pkey, &pubkey, size) != NULL;
  }
  
  bool CECKey::Verify(const uint256& hash, const std::vector<unsigned char>& vchSig)
  {
      if (vchSig.empty())
          return false;
  
      // New versions of OpenSSL will reject non-canonical DER signatures. de/re-serialize first.
      unsigned char* norm_der = NULL;
      ECDSA_SIG* norm_sig = ECDSA_SIG_new();
      const unsigned char* sigptr = &vchSig[0];
      assert(norm_sig);
      if (d2i_ECDSA_SIG(&norm_sig, &sigptr, vchSig.size()) == NULL) {
          /* As of OpenSSL 1.0.0p d2i_ECDSA_SIG frees and nulls the pointer on
           * error. But OpenSSL's own use of this function redundantly frees the
           * result. As ECDSA_SIG_free(NULL) is a no-op, and in the absence of a
           * clear contract for the function behaving the same way is more
           * conservative.
           */
          ECDSA_SIG_free(norm_sig);
          return false;
      }
      int derlen = i2d_ECDSA_SIG(norm_sig, &norm_der);
      ECDSA_SIG_free(norm_sig);
      if (derlen <= 0)
          return false;
  
      // -1 = error, 0 = bad sig, 1 = good
      bool ret = ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), norm_der, derlen, pkey) == 1;
      OPENSSL_free(norm_der);
      return ret;
  }
  
  bool CECKey::Recover(const uint256& hash, const unsigned char* p64, int rec)
  {
      if (rec < 0 || rec >= 3)
          return false;
      ECDSA_SIG* sig = ECDSA_SIG_new();
      BN_bin2bn(&p64[0], 32, sig->r);
      BN_bin2bn(&p64[32], 32, sig->s);
      bool ret = ECDSA_SIG_recover_key_GFp(pkey, sig, (unsigned char*)&hash, sizeof(hash), rec, 0) == 1;
      ECDSA_SIG_free(sig);
      return ret;
  }
  
  bool CECKey::TweakPublic(const unsigned char vchTweak[32])
  {
      bool ret = true;
      BN_CTX* ctx = BN_CTX_new();
      BN_CTX_start(ctx);
      BIGNUM* bnTweak = BN_CTX_get(ctx);
      BIGNUM* bnOrder = BN_CTX_get(ctx);
      BIGNUM* bnOne = BN_CTX_get(ctx);
      const EC_GROUP* group = EC_KEY_get0_group(pkey);
      EC_GROUP_get_order(group, bnOrder, ctx); // what a grossly inefficient way to get the (constant) group order...
      BN_bin2bn(vchTweak, 32, bnTweak);
      if (BN_cmp(bnTweak, bnOrder) >= 0)
          ret = false; // extremely unlikely
      EC_POINT* point = EC_POINT_dup(EC_KEY_get0_public_key(pkey), group);
      BN_one(bnOne);
      EC_POINT_mul(group, point, bnTweak, point, bnOne, ctx);
      if (EC_POINT_is_at_infinity(group, point))
          ret = false; // ridiculously unlikely
      EC_KEY_set_public_key(pkey, point);
      EC_POINT_free(point);
      BN_CTX_end(ctx);
      BN_CTX_free(ctx);
      return ret;
  }
  
  bool CECKey::SanityCheck()
  {
      EC_KEY* pkey = EC_KEY_new_by_curve_name(NID_secp256k1);
      if (pkey == NULL)
          return false;
      EC_KEY_free(pkey);
  
      // TODO Is there more EC functionality that could be missing?
      return true;
  }
  