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Use 'low S' as malleability breaker rather than 'even S'

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This commit is contained in:
Pieter Wuille 2013-09-18 23:37:05 +02:00
parent 9196f38c8f
commit e0e14e43d9
1 changed files with 11 additions and 9 deletions
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8
src/key.cpp
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@ -199,17 +199,19 @@ public:
ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey); ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey);
if (sig == NULL) if (sig == NULL)
return false; return false;
if (BN_is_odd(sig->s)) {
// enforce even S values, by negating the value (modulo the order) if odd
BN_CTX *ctx = BN_CTX_new(); BN_CTX *ctx = BN_CTX_new();
BN_CTX_start(ctx); BN_CTX_start(ctx);
const EC_GROUP *group = EC_KEY_get0_group(pkey); const EC_GROUP *group = EC_KEY_get0_group(pkey);
BIGNUM *order = BN_CTX_get(ctx); BIGNUM *order = BN_CTX_get(ctx);
BIGNUM *halforder = BN_CTX_get(ctx);
EC_GROUP_get_order(group, order, 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_sub(sig->s, order, sig->s);
}
BN_CTX_end(ctx); BN_CTX_end(ctx);
BN_CTX_free(ctx); BN_CTX_free(ctx);
}
unsigned int nSize = ECDSA_size(pkey); unsigned int nSize = ECDSA_size(pkey);
vchSig.resize(nSize); // Make sure it is big enough vchSig.resize(nSize); // Make sure it is big enough
unsigned char *pos = &vchSig[0]; unsigned char *pos = &vchSig[0];