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authorPieter Wuille <pieter.wuille@gmail.com>2011-04-25 13:23:29 +0200
committerPieter Wuille <pieter.wuille@gmail.com>2011-09-27 19:48:22 +0200
commit01cc526318ff9f0ee6fb675ffe3be4ca7f3cda7a (patch)
tree1b76eabfd7fe0fc424acaf8e213298e9e4f71181 /src/key.h
parentd9867551fc58ebb62eddef3dfbdb1dc711110577 (diff)
Compact signatures and key recovery
Introduce a new type of signatures that are only 65 bytes long, and allow reconstruction of the public key that was used to create the signature.
Diffstat (limited to 'src/key.h')
-rw-r--r--src/key.h140
1 files changed, 140 insertions, 0 deletions
diff --git a/src/key.h b/src/key.h
index d2e6689456..5ffd7b9ccc 100644
--- a/src/key.h
+++ b/src/key.h
@@ -75,6 +75,76 @@ err:
return(ok);
}
+int static inline 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;
+}
class key_error : public std::runtime_error
{
@@ -221,6 +291,66 @@ public:
return true;
}
+ // create a compact signature (65 bytes), which allows reconstructing the used public key
+ bool SignCompact(uint256 hash, std::vector<unsigned char>& vchSig)
+ {
+ bool fOk = false;
+ ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey);
+ if (sig==NULL)
+ return false;
+ vchSig.clear();
+ vchSig.resize(65,0);
+ int nBitsR = BN_num_bits(sig->r);
+ int nBitsS = BN_num_bits(sig->s);
+ if (nBitsR <= 256 && nBitsS <= 256)
+ {
+ int nRecId = -1;
+ for (int i=0; i<4; i++)
+ {
+ CKey keyRec;
+ keyRec.fSet = true;
+ if (ECDSA_SIG_recover_key_GFp(keyRec.pkey, sig, (unsigned char*)&hash, sizeof(hash), i, 1) == 1)
+ if (keyRec.GetPubKey() == this->GetPubKey())
+ {
+ nRecId = i;
+ break;
+ }
+ }
+
+ if (nRecId == -1)
+ throw key_error("CKEy::SignCompact() : unable to construct recoverable key");
+
+ vchSig[0] = nRecId+27;
+ BN_bn2bin(sig->r,&vchSig[33-(nBitsR+7)/8]);
+ BN_bn2bin(sig->s,&vchSig[65-(nBitsS+7)/8]);
+ fOk = true;
+ }
+ ECDSA_SIG_free(sig);
+ return fOk;
+ }
+
+ // reconstruct public key from a compact signature
+ bool SetCompactSignature(uint256 hash, const std::vector<unsigned char>& vchSig)
+ {
+ if (vchSig.size() != 65)
+ return false;
+ if (vchSig[0]<27 || vchSig[0]>=31)
+ return false;
+ ECDSA_SIG *sig = ECDSA_SIG_new();
+ BN_bin2bn(&vchSig[1],32,sig->r);
+ BN_bin2bn(&vchSig[33],32,sig->s);
+
+ EC_KEY_free(pkey);
+ pkey = EC_KEY_new_by_curve_name(NID_secp256k1);
+ if (ECDSA_SIG_recover_key_GFp(pkey, sig, (unsigned char*)&hash, sizeof(hash), vchSig[0] - 27, 0) == 1)
+ {
+ fSet = true;
+ ECDSA_SIG_free(sig);
+ return true;
+ }
+ return false;
+ }
+
bool Verify(uint256 hash, const std::vector<unsigned char>& vchSig)
{
// -1 = error, 0 = bad sig, 1 = good
@@ -229,6 +359,16 @@ public:
return true;
}
+ bool VerifyCompact(uint256 hash, const std::vector<unsigned char>& vchSig)
+ {
+ CKey key;
+ if (!key.SetCompactSignature(hash, vchSig))
+ return false;
+ if (GetPubKey() != key.GetPubKey())
+ return false;
+ return true;
+ }
+
CBitcoinAddress GetAddress() const
{
return CBitcoinAddress(GetPubKey());