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 class ecgroup_order
  17 {
  18 public:
  19   static const EC_GROUP* get()
  20   {
  21       static const ecgroup_order wrapper;
  22       return wrapper.pgroup;
  23   }
  24
  25 private:
  26   ecgroup_order()
  27   : pgroup(EC_GROUP_new_by_curve_name(NID_secp256k1))
  28   {
  29   }
  30
  31   ~ecgroup_order()
  32   {
  33     EC_GROUP_free(pgroup);
  34   }
  35
  36   EC_GROUP* pgroup;
  37 };
  38
  39 /**
  40  * Perform ECDSA key recovery (see SEC1 4.1.6) for curves over (mod p)-fields
  41  * recid selects which key is recovered
  42  * if check is non-zero, additional checks are performed
  43  */
  44 int ECDSA_SIG_recover_key_GFp(EC_KEY *eckey, ECDSA_SIG *ecsig, const unsigned char *msg, int msglen, int recid, int check)
  45 {
  46     if (!eckey) return 0;
  47
  48     int ret = 0;
  49     BN_CTX *ctx = NULL;
  50
  51     BIGNUM *x = NULL;
  52     BIGNUM *e = NULL;
  53     BIGNUM *order = NULL;
  54     BIGNUM *sor = NULL;
  55     BIGNUM *eor = NULL;
  56     BIGNUM *field = NULL;
  57     EC_POINT *R = NULL;
  58     EC_POINT *O = NULL;
  59     EC_POINT *Q = NULL;
  60     BIGNUM *rr = NULL;
  61     BIGNUM *zero = NULL;
  62     int n = 0;
  63     int i = recid / 2;
  64
  65     const EC_GROUP *group = EC_KEY_get0_group(eckey);
  66     if ((ctx = BN_CTX_new()) == NULL) { ret = -1; goto err; }
  67     BN_CTX_start(ctx);
  68     order = BN_CTX_get(ctx);
  69     if (!EC_GROUP_get_order(group, order, ctx)) { ret = -2; goto err; }
  70     x = BN_CTX_get(ctx);
  71     if (!BN_copy(x, order)) { ret=-1; goto err; }
  72     if (!BN_mul_word(x, i)) { ret=-1; goto err; }
  73     if (!BN_add(x, x, ecsig->r)) { ret=-1; goto err; }
  74     field = BN_CTX_get(ctx);
  75     if (!EC_GROUP_get_curve_GFp(group, field, NULL, NULL, ctx)) { ret=-2; goto err; }
  76     if (BN_cmp(x, field) >= 0) { ret=0; goto err; }
  77     if ((R = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
  78     if (!EC_POINT_set_compressed_coordinates_GFp(group, R, x, recid % 2, ctx)) { ret=0; goto err; }
  79     if (check)
  80     {
  81         if ((O = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
  82         if (!EC_POINT_mul(group, O, NULL, R, order, ctx)) { ret=-2; goto err; }
  83         if (!EC_POINT_is_at_infinity(group, O)) { ret = 0; goto err; }
  84     }
  85     if ((Q = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
  86     n = EC_GROUP_get_degree(group);
  87     e = BN_CTX_get(ctx);
  88     if (!BN_bin2bn(msg, msglen, e)) { ret=-1; goto err; }
  89     if (8*msglen > n) BN_rshift(e, e, 8-(n & 7));
  90     zero = BN_CTX_get(ctx);
  91     if (!BN_zero(zero)) { ret=-1; goto err; }
  92     if (!BN_mod_sub(e, zero, e, order, ctx)) { ret=-1; goto err; }
  93     rr = BN_CTX_get(ctx);
  94     if (!BN_mod_inverse(rr, ecsig->r, order, ctx)) { ret=-1; goto err; }
  95     sor = BN_CTX_get(ctx);
  96     if (!BN_mod_mul(sor, ecsig->s, rr, order, ctx)) { ret=-1; goto err; }
  97     eor = BN_CTX_get(ctx);
  98     if (!BN_mod_mul(eor, e, rr, order, ctx)) { ret=-1; goto err; }
  99     if (!EC_POINT_mul(group, Q, eor, R, sor, ctx)) { ret=-2; goto err; }
 100     if (!EC_KEY_set_public_key(eckey, Q)) { ret=-2; goto err; }
 101
 102     ret = 1;
 103
 104 err:
 105     if (ctx) {
 106         BN_CTX_end(ctx);
 107         BN_CTX_free(ctx);
 108     }
 109     if (R != NULL) EC_POINT_free(R);
 110     if (O != NULL) EC_POINT_free(O);
 111     if (Q != NULL) EC_POINT_free(Q);
 112     return ret;
 113 }
 114
 115 } // anon namespace
 116
 117 CECKey::CECKey() {
 118     pkey = EC_KEY_new();
 119     assert(pkey != NULL);
 120     int result = EC_KEY_set_group(pkey, ecgroup_order::get());
 121     assert(result);
 122 }
 123
 124 CECKey::~CECKey() {
 125     EC_KEY_free(pkey);
 126 }
 127
 128 void CECKey::GetPubKey(std::vector<unsigned char> &pubkey, bool fCompressed) {
 129     EC_KEY_set_conv_form(pkey, fCompressed ? POINT_CONVERSION_COMPRESSED : POINT_CONVERSION_UNCOMPRESSED);
 130     int nSize = i2o_ECPublicKey(pkey, NULL);
 131     assert(nSize);
 132     assert(nSize <= 65);
 133     pubkey.clear();
 134     pubkey.resize(nSize);
 135     unsigned char *pbegin(begin_ptr(pubkey));
 136     int nSize2 = i2o_ECPublicKey(pkey, &pbegin);
 137     assert(nSize == nSize2);
 138 }
 139
 140 bool CECKey::SetPubKey(const unsigned char* pubkey, size_t size) {
 141     return o2i_ECPublicKey(&pkey, &pubkey, size) != NULL;
 142 }
 143
 144 bool CECKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
 145     if (vchSig.empty())
 146         return false;
 147
 148     // New versions of OpenSSL will reject non-canonical DER signatures. de/re-serialize first.
 149     unsigned char *norm_der = NULL;
 150     ECDSA_SIG *norm_sig = ECDSA_SIG_new();
 151     const unsigned char* sigptr = &vchSig[0];
 152     assert(norm_sig);
 153     if (d2i_ECDSA_SIG(&norm_sig, &sigptr, vchSig.size()) == NULL)
 154     {
 155         /* As of OpenSSL 1.0.0p d2i_ECDSA_SIG frees and nulls the pointer on
 156          * error. But OpenSSL's own use of this function redundantly frees the
 157          * result. As ECDSA_SIG_free(NULL) is a no-op, and in the absence of a
 158          * clear contract for the function behaving the same way is more
 159          * conservative.
 160          */
 161         ECDSA_SIG_free(norm_sig);
 162         return false;
 163     }
 164     int derlen = i2d_ECDSA_SIG(norm_sig, &norm_der);
 165     ECDSA_SIG_free(norm_sig);
 166     if (derlen <= 0)
 167         return false;
 168
 169     // -1 = error, 0 = bad sig, 1 = good
 170     bool ret = ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), norm_der, derlen, pkey) == 1;
 171     OPENSSL_free(norm_der);
 172     return ret;
 173 }
 174
 175 bool CECKey::Recover(const uint256 &hash, const unsigned char *p64, int rec)
 176 {
 177     if (rec<0 || rec>=3)
 178         return false;
 179     ECDSA_SIG *sig = ECDSA_SIG_new();
 180     BN_bin2bn(&p64[0],  32, sig->r);
 181     BN_bin2bn(&p64[32], 32, sig->s);
 182     bool ret = ECDSA_SIG_recover_key_GFp(pkey, sig, (unsigned char*)&hash, sizeof(hash), rec, 0) == 1;
 183     ECDSA_SIG_free(sig);
 184     return ret;
 185 }
 186
 187 bool CECKey::TweakPublic(const unsigned char vchTweak[32]) {
 188     bool ret = true;
 189     BN_CTX *ctx = BN_CTX_new();
 190     BN_CTX_start(ctx);
 191     BIGNUM *bnTweak = BN_CTX_get(ctx);
 192     BIGNUM *bnOrder = BN_CTX_get(ctx);
 193     BIGNUM *bnOne = BN_CTX_get(ctx);
 194     const EC_GROUP *group = EC_KEY_get0_group(pkey);
 195     EC_GROUP_get_order(group, bnOrder, ctx); // what a grossly inefficient way to get the (constant) group order...
 196     BN_bin2bn(vchTweak, 32, bnTweak);
 197     if (BN_cmp(bnTweak, bnOrder) >= 0)
 198         ret = false; // extremely unlikely
 199     EC_POINT *point = EC_POINT_dup(EC_KEY_get0_public_key(pkey), group);
 200     BN_one(bnOne);
 201     EC_POINT_mul(group, point, bnTweak, point, bnOne, ctx);
 202     if (EC_POINT_is_at_infinity(group, point))
 203         ret = false; // ridiculously unlikely
 204     EC_KEY_set_public_key(pkey, point);
 205     EC_POINT_free(point);
 206     BN_CTX_end(ctx);
 207     BN_CTX_free(ctx);
 208     return ret;
 209 }
 210
 211 bool CECKey::SanityCheck()
 212 {
 213     const EC_GROUP *pgroup = ecgroup_order::get();
 214     if(pgroup == NULL)
 215         return false;
 216     // TODO Is there more EC functionality that could be missing?
 217     return true;
 218 }