Remove unneeded lax ECDSA signature verification.
Signed-off-by: Daira Hopwood <daira@jacaranda.org>
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161
src/pubkey.cpp
161
src/pubkey.cpp
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@ -14,158 +14,6 @@ namespace
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secp256k1_context* secp256k1_context_verify = NULL;
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}
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/** This function is taken from the libsecp256k1 distribution and implements
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* DER parsing for ECDSA signatures, while supporting an arbitrary subset of
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* format violations.
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*
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* Supported violations include negative integers, excessive padding, garbage
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* at the end, and overly long length descriptors. This is safe to use in
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* Bitcoin because since the activation of BIP66, signatures are verified to be
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* strict DER before being passed to this module, and we know it supports all
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* violations present in the blockchain before that point.
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*/
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static int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen) {
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size_t rpos, rlen, spos, slen;
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size_t pos = 0;
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size_t lenbyte;
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unsigned char tmpsig[64] = {0};
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int overflow = 0;
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/* Hack to initialize sig with a correctly-parsed but invalid signature. */
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secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
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/* Sequence tag byte */
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if (pos == inputlen || input[pos] != 0x30) {
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return 0;
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}
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pos++;
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/* Sequence length bytes */
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if (pos == inputlen) {
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return 0;
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}
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lenbyte = input[pos++];
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if (lenbyte & 0x80) {
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lenbyte -= 0x80;
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if (lenbyte > inputlen - pos) {
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return 0;
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}
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pos += lenbyte;
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}
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/* Integer tag byte for R */
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if (pos == inputlen || input[pos] != 0x02) {
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return 0;
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}
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pos++;
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/* Integer length for R */
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if (pos == inputlen) {
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return 0;
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}
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lenbyte = input[pos++];
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if (lenbyte & 0x80) {
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lenbyte -= 0x80;
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if (lenbyte > inputlen - pos) {
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return 0;
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}
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while (lenbyte > 0 && input[pos] == 0) {
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pos++;
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lenbyte--;
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}
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static_assert(sizeof(size_t) >= 4, "size_t too small");
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if (lenbyte >= 4) {
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return 0;
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}
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rlen = 0;
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while (lenbyte > 0) {
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rlen = (rlen << 8) + input[pos];
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pos++;
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lenbyte--;
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}
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} else {
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rlen = lenbyte;
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}
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if (rlen > inputlen - pos) {
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return 0;
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}
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rpos = pos;
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pos += rlen;
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/* Integer tag byte for S */
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if (pos == inputlen || input[pos] != 0x02) {
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return 0;
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}
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pos++;
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/* Integer length for S */
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if (pos == inputlen) {
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return 0;
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}
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lenbyte = input[pos++];
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if (lenbyte & 0x80) {
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lenbyte -= 0x80;
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if (lenbyte > inputlen - pos) {
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return 0;
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}
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while (lenbyte > 0 && input[pos] == 0) {
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pos++;
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lenbyte--;
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}
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static_assert(sizeof(size_t) >= 4, "size_t too small");
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if (lenbyte >= 4) {
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return 0;
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}
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slen = 0;
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while (lenbyte > 0) {
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slen = (slen << 8) + input[pos];
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pos++;
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lenbyte--;
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}
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} else {
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slen = lenbyte;
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}
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if (slen > inputlen - pos) {
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return 0;
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}
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spos = pos;
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pos += slen;
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/* Ignore leading zeroes in R */
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while (rlen > 0 && input[rpos] == 0) {
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rlen--;
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rpos++;
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}
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/* Copy R value */
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if (rlen > 32) {
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overflow = 1;
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} else {
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memcpy(tmpsig + 32 - rlen, input + rpos, rlen);
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}
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/* Ignore leading zeroes in S */
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while (slen > 0 && input[spos] == 0) {
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slen--;
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spos++;
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}
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/* Copy S value */
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if (slen > 32) {
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overflow = 1;
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} else {
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memcpy(tmpsig + 64 - slen, input + spos, slen);
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}
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if (!overflow) {
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overflow = !secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
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}
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if (overflow) {
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/* Overwrite the result again with a correctly-parsed but invalid
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signature if parsing failed. */
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memset(tmpsig, 0, 64);
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secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
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}
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return 1;
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}
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bool CPubKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) const {
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if (!IsValid())
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@ -178,11 +26,12 @@ bool CPubKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchS
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if (vchSig.size() == 0) {
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return false;
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}
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if (!ecdsa_signature_parse_der_lax(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) {
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/* Zcash, unlike Bitcoin, has always enforced strict DER signatures. */
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if (!secp256k1_ecdsa_signature_parse_der(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) {
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return false;
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}
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/* libsecp256k1's ECDSA verification requires lower-S signatures, which have
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* not historically been enforced in Bitcoin, so normalize them first. */
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* not historically been enforced in Bitcoin or Zcash, so normalize them first. */
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secp256k1_ecdsa_signature_normalize(secp256k1_context_verify, &sig, &sig);
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return secp256k1_ecdsa_verify(secp256k1_context_verify, &sig, hash.begin(), &pubkey);
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}
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@ -277,7 +126,9 @@ bool CExtPubKey::Derive(CExtPubKey &out, unsigned int nChild) const {
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/* static */ bool CPubKey::CheckLowS(const std::vector<unsigned char>& vchSig) {
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secp256k1_ecdsa_signature sig;
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if (!ecdsa_signature_parse_der_lax(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) {
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/* Zcash, unlike Bitcoin, has always enforced strict DER signatures. */
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if (!secp256k1_ecdsa_signature_parse_der(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) {
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return false;
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}
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return (!secp256k1_ecdsa_signature_normalize(secp256k1_context_verify, NULL, &sig));
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