src/ecwrapper.cpp

   1 // Copyright (c) 2009-2014 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #include "ecwrapper.h"
   6
   7 #include "serialize.h"
   8 #include "uint256.h"
   9
  10 #include <openssl/bn.h>
  11 #include <openssl/ecdsa.h>
  12 #include <openssl/obj_mac.h>
  13
  14 namespace {
  15
  16 /**
  17  * Perform ECDSA key recovery (see SEC1 4.1.6) for curves over (mod p)-fields
  18  * recid selects which key is recovered
  19  * if check is non-zero, additional checks are performed
  20  */
  21 int ECDSA_SIG_recover_key_GFp(EC_KEY *eckey, ECDSA_SIG *ecsig, const unsigned char *msg, int msglen, int recid, int check)
  22 {
  23     if (!eckey) return 0;
  24
  25     int ret = 0;
  26     BN_CTX *ctx = NULL;
  27
  28     BIGNUM *x = NULL;
  29     BIGNUM *e = NULL;
  30     BIGNUM *order = NULL;
  31     BIGNUM *sor = NULL;
  32     BIGNUM *eor = NULL;
  33     BIGNUM *field = NULL;
  34     EC_POINT *R = NULL;
  35     EC_POINT *O = NULL;
  36     EC_POINT *Q = NULL;
  37     BIGNUM *rr = NULL;
  38     BIGNUM *zero = NULL;
  39     int n = 0;
  40     int i = recid / 2;
  41
  42     const EC_GROUP *group = EC_KEY_get0_group(eckey);
  43     if ((ctx = BN_CTX_new()) == NULL) { ret = -1; goto err; }
  44     BN_CTX_start(ctx);
  45     order = BN_CTX_get(ctx);
  46     if (!EC_GROUP_get_order(group, order, ctx)) { ret = -2; goto err; }
  47     x = BN_CTX_get(ctx);
  48     if (!BN_copy(x, order)) { ret=-1; goto err; }
  49     if (!BN_mul_word(x, i)) { ret=-1; goto err; }
  50     if (!BN_add(x, x, ecsig->r)) { ret=-1; goto err; }
  51     field = BN_CTX_get(ctx);
  52     if (!EC_GROUP_get_curve_GFp(group, field, NULL, NULL, ctx)) { ret=-2; goto err; }
  53     if (BN_cmp(x, field) >= 0) { ret=0; goto err; }
  54     if ((R = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
  55     if (!EC_POINT_set_compressed_coordinates_GFp(group, R, x, recid % 2, ctx)) { ret=0; goto err; }
  56     if (check)
  57     {
  58         if ((O = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
  59         if (!EC_POINT_mul(group, O, NULL, R, order, ctx)) { ret=-2; goto err; }
  60         if (!EC_POINT_is_at_infinity(group, O)) { ret = 0; goto err; }
  61     }
  62     if ((Q = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
  63     n = EC_GROUP_get_degree(group);
  64     e = BN_CTX_get(ctx);
  65     if (!BN_bin2bn(msg, msglen, e)) { ret=-1; goto err; }
  66     if (8*msglen > n) BN_rshift(e, e, 8-(n & 7));
  67     zero = BN_CTX_get(ctx);
  68     if (!BN_zero(zero)) { ret=-1; goto err; }
  69     if (!BN_mod_sub(e, zero, e, order, ctx)) { ret=-1; goto err; }
  70     rr = BN_CTX_get(ctx);
  71     if (!BN_mod_inverse(rr, ecsig->r, order, ctx)) { ret=-1; goto err; }
  72     sor = BN_CTX_get(ctx);
  73     if (!BN_mod_mul(sor, ecsig->s, rr, order, ctx)) { ret=-1; goto err; }
  74     eor = BN_CTX_get(ctx);
  75     if (!BN_mod_mul(eor, e, rr, order, ctx)) { ret=-1; goto err; }
  76     if (!EC_POINT_mul(group, Q, eor, R, sor, ctx)) { ret=-2; goto err; }
  77     if (!EC_KEY_set_public_key(eckey, Q)) { ret=-2; goto err; }
  78
  79     ret = 1;
  80
  81 err:
  82     if (ctx) {
  83         BN_CTX_end(ctx);
  84         BN_CTX_free(ctx);
  85     }
  86     if (R != NULL) EC_POINT_free(R);
  87     if (O != NULL) EC_POINT_free(O);
  88     if (Q != NULL) EC_POINT_free(Q);
  89     return ret;
  90 }
  91
  92 } // anon namespace
  93
  94 CECKey::CECKey() {
  95     pkey = EC_KEY_new_by_curve_name(NID_secp256k1);
  96     assert(pkey != NULL);
  97 }
  98
  99 CECKey::~CECKey() {
 100     EC_KEY_free(pkey);
 101 }
 102
 103 void CECKey::GetPubKey(std::vector<unsigned char> &pubkey, bool fCompressed) {
 104     EC_KEY_set_conv_form(pkey, fCompressed ? POINT_CONVERSION_COMPRESSED : POINT_CONVERSION_UNCOMPRESSED);
 105     int nSize = i2o_ECPublicKey(pkey, NULL);
 106     assert(nSize);
 107     assert(nSize <= 65);
 108     pubkey.clear();
 109     pubkey.resize(nSize);
 110     unsigned char *pbegin(begin_ptr(pubkey));
 111     int nSize2 = i2o_ECPublicKey(pkey, &pbegin);
 112     assert(nSize == nSize2);
 113 }
 114
 115 bool CECKey::SetPubKey(const unsigned char* pubkey, size_t size) {
 116     return o2i_ECPublicKey(&pkey, &pubkey, size) != NULL;
 117 }
 118
 119 bool CECKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
 120     if (vchSig.empty())
 121         return false;
 122
 123     // New versions of OpenSSL will reject non-canonical DER signatures. de/re-serialize first.
 124     unsigned char *norm_der = NULL;
 125     ECDSA_SIG *norm_sig = ECDSA_SIG_new();
 126     const unsigned char* sigptr = &vchSig[0];
 127     assert(norm_sig);
 128     if (d2i_ECDSA_SIG(&norm_sig, &sigptr, vchSig.size()) == NULL)
 129     {
 130         /* As of OpenSSL 1.0.0p d2i_ECDSA_SIG frees and nulls the pointer on
 131          * error. But OpenSSL's own use of this function redundantly frees the
 132          * result. As ECDSA_SIG_free(NULL) is a no-op, and in the absence of a
 133          * clear contract for the function behaving the same way is more
 134          * conservative.
 135          */
 136         ECDSA_SIG_free(norm_sig);
 137         return false;
 138     }
 139     int derlen = i2d_ECDSA_SIG(norm_sig, &norm_der);
 140     ECDSA_SIG_free(norm_sig);
 141     if (derlen <= 0)
 142         return false;
 143
 144     // -1 = error, 0 = bad sig, 1 = good
 145     bool ret = ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), norm_der, derlen, pkey) == 1;
 146     OPENSSL_free(norm_der);
 147     return ret;
 148 }
 149
 150 bool CECKey::Recover(const uint256 &hash, const unsigned char *p64, int rec)
 151 {
 152     if (rec<0 || rec>=3)
 153         return false;
 154     ECDSA_SIG *sig = ECDSA_SIG_new();
 155     BN_bin2bn(&p64[0],  32, sig->r);
 156     BN_bin2bn(&p64[32], 32, sig->s);
 157     bool ret = ECDSA_SIG_recover_key_GFp(pkey, sig, (unsigned char*)&hash, sizeof(hash), rec, 0) == 1;
 158     ECDSA_SIG_free(sig);
 159     return ret;
 160 }
 161
 162 bool CECKey::TweakPublic(const unsigned char vchTweak[32]) {
 163     bool ret = true;
 164     BN_CTX *ctx = BN_CTX_new();
 165     BN_CTX_start(ctx);
 166     BIGNUM *bnTweak = BN_CTX_get(ctx);
 167     BIGNUM *bnOrder = BN_CTX_get(ctx);
 168     BIGNUM *bnOne = BN_CTX_get(ctx);
 169     const EC_GROUP *group = EC_KEY_get0_group(pkey);
 170     EC_GROUP_get_order(group, bnOrder, ctx); // what a grossly inefficient way to get the (constant) group order...
 171     BN_bin2bn(vchTweak, 32, bnTweak);
 172     if (BN_cmp(bnTweak, bnOrder) >= 0)
 173         ret = false; // extremely unlikely
 174     EC_POINT *point = EC_POINT_dup(EC_KEY_get0_public_key(pkey), group);
 175     BN_one(bnOne);
 176     EC_POINT_mul(group, point, bnTweak, point, bnOne, ctx);
 177     if (EC_POINT_is_at_infinity(group, point))
 178         ret = false; // ridiculously unlikely
 179     EC_KEY_set_public_key(pkey, point);
 180     EC_POINT_free(point);
 181     BN_CTX_end(ctx);
 182     BN_CTX_free(ctx);
 183     return ret;
 184 }
 185
 186 bool CECKey::SanityCheck()
 187 {
 188     EC_KEY *pkey = EC_KEY_new_by_curve_name(NID_secp256k1);
 189     if(pkey == NULL)
 190         return false;
 191     EC_KEY_free(pkey);
 192
 193     // TODO Is there more EC functionality that could be missing?
 194     return true;
 195 }