src/eckey.cpp
// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2013 The Bitcoin developers
// Copyright (c) 2014-2015 The ShadowCoin developers
// Distributed under the MIT/X11 software license, see the accompanying
// file license.txt or http://www.opensource.org/licenses/mit-license.php.
#include "eckey.h"
// anonymous namespace with local implementation code (OpenSSL interaction)
namespace {
// Generate a private key from just the secret parameter
int EC_KEY_regenerate_key(EC_KEY *eckey, BIGNUM *priv_key)
{
int ok = 0;
BN_CTX *ctx = NULL;
EC_POINT *pub_key = NULL;
if (!eckey) return 0;
const EC_GROUP *group = EC_KEY_get0_group(eckey);
if ((ctx = BN_CTX_new()) == NULL)
goto err;
pub_key = EC_POINT_new(group);
if (pub_key == NULL)
goto err;
if (!EC_POINT_mul(group, pub_key, priv_key, NULL, NULL, ctx))
goto err;
EC_KEY_set_private_key(eckey,priv_key);
EC_KEY_set_public_key(eckey,pub_key);
ok = 1;
err:
if (pub_key)
EC_POINT_free(pub_key);
if (ctx != NULL)
BN_CTX_free(ctx);
return(ok);
}
// 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;
}
}; // end of anonymous namespace
void CECKey::GetSecretBytes(unsigned char vch[32]) const
{
const BIGNUM *bn = EC_KEY_get0_private_key(pkey);
assert(bn);
int nBytes = BN_num_bytes(bn);
int n=BN_bn2bin(bn,&vch[32 - nBytes]);
assert(n == nBytes);
memset(vch, 0, 32 - nBytes);
}
void CECKey::SetSecretBytes(const unsigned char vch[32])
{
BIGNUM bn;
BN_init(&bn);
assert(BN_bin2bn(vch, 32, &bn));
assert(EC_KEY_regenerate_key(pkey, &bn));
BN_clear_free(&bn);
}
void CECKey::GetPrivKey(CPrivKey &privkey, bool fCompressed) {
EC_KEY_set_conv_form(pkey, fCompressed ? POINT_CONVERSION_COMPRESSED : POINT_CONVERSION_UNCOMPRESSED);
int nSize = i2d_ECPrivateKey(pkey, NULL);
assert(nSize);
privkey.resize(nSize);
unsigned char* pbegin = &privkey[0];
int nSize2 = i2d_ECPrivateKey(pkey, &pbegin);
assert(nSize == nSize2);
}
bool CECKey::SetPrivKey(const CPrivKey &privkey, bool fSkipCheck) {
const unsigned char* pbegin = &privkey[0];
if (d2i_ECPrivateKey(&pkey, &pbegin, privkey.size())) {
if(fSkipCheck)
return true;
// d2i_ECPrivateKey returns true if parsing succeeds.
// This doesn't necessarily mean the key is valid.
if (EC_KEY_check_key(pkey))
return true;
}
return false;
}
void CECKey::GetPubKey(CPubKey &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);
unsigned char c[65];
unsigned char *pbegin = c;
int nSize2 = i2o_ECPublicKey(pkey, &pbegin);
assert(nSize == nSize2);
pubkey.Set(&c[0], &c[nSize]);
}
bool CECKey::SetPubKey(const CPubKey &pubkey) {
const unsigned char* pbegin = pubkey.begin();
return o2i_ECPublicKey(&pkey, &pbegin, pubkey.size());
}
bool CECKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig) {
vchSig.clear();
ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey);
if (sig == NULL)
return false;
BN_CTX *ctx = BN_CTX_new();
BN_CTX_start(ctx);
const EC_GROUP *group = EC_KEY_get0_group(pkey);
BIGNUM *order = BN_CTX_get(ctx);
BIGNUM *halforder = BN_CTX_get(ctx);
EC_GROUP_get_order(group, order, ctx);
BN_rshift1(halforder, order);
if (BN_cmp(sig->s, halforder) > 0) {
// enforce low S values, by negating the value (modulo the order) if above order/2.
BN_sub(sig->s, order, sig->s);
}
BN_CTX_end(ctx);
BN_CTX_free(ctx);
unsigned int nSize = ECDSA_size(pkey);
vchSig.resize(nSize); // Make sure it is big enough
unsigned char *pos = &vchSig[0];
nSize = i2d_ECDSA_SIG(sig, &pos);
ECDSA_SIG_free(sig);
vchSig.resize(nSize); // Shrink to fit actual size
return true;
}
bool CECKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
// -1 = error, 0 = bad sig, 1 = good
if (ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), &vchSig[0], vchSig.size(), pkey) != 1)
return false;
return true;
}
bool CECKey::SignCompact(const uint256 &hash, unsigned char *p64, int &rec) {
bool fOk = false;
ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey);
if (sig==NULL)
return false;
memset(p64, 0, 64);
int nBitsR = BN_num_bits(sig->r);
int nBitsS = BN_num_bits(sig->s);
if (nBitsR <= 256 && nBitsS <= 256) {
CPubKey pubkey;
GetPubKey(pubkey, true);
for (int i=0; i<4; i++) {
CECKey keyRec;
if (ECDSA_SIG_recover_key_GFp(keyRec.pkey, sig, (unsigned char*)&hash, sizeof(hash), i, 1) == 1) {
CPubKey pubkeyRec;
keyRec.GetPubKey(pubkeyRec, true);
if (pubkeyRec == pubkey) {
rec = i;
fOk = true;
break;
}
}
}
assert(fOk);
BN_bn2bin(sig->r,&p64[32-(nBitsR+7)/8]);
BN_bn2bin(sig->s,&p64[64-(nBitsS+7)/8]);
}
ECDSA_SIG_free(sig);
return fOk;
}
// reconstruct public key from a compact signature
// This is only slightly more CPU intensive than just verifying it.
// If this function succeeds, the recovered public key is guaranteed to be valid
// (the signature is a valid signature of the given data for that key)
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 TweakSecret(unsigned char vchSecretOut[32], const unsigned char vchSecretIn[32], const unsigned char vchTweak[32])
{
bool ret = true;
BN_CTX *ctx = BN_CTX_new();
BN_CTX_start(ctx);
BIGNUM *bnSecret = BN_CTX_get(ctx);
BIGNUM *bnTweak = BN_CTX_get(ctx);
BIGNUM *bnOrder = BN_CTX_get(ctx);
EC_GROUP *group = EC_GROUP_new_by_curve_name(NID_secp256k1);
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
BN_bin2bn(vchSecretIn, 32, bnSecret);
BN_add(bnSecret, bnSecret, bnTweak);
BN_nnmod(bnSecret, bnSecret, bnOrder, ctx);
if (BN_is_zero(bnSecret))
ret = false; // ridiculously unlikely
int nBits = BN_num_bits(bnSecret);
memset(vchSecretOut, 0, 32);
BN_bn2bin(bnSecret, &vchSecretOut[32-(nBits+7)/8]);
EC_GROUP_free(group);
BN_CTX_end(ctx);
BN_CTX_free(ctx);
return ret;
}