From 6e182686163ce3c15b878bd78c41d8d18db344f1 Mon Sep 17 00:00:00 2001 From: Pieter Wuille Date: Tue, 28 Jul 2015 20:11:20 +0200 Subject: Switch to libsecp256k1-based validation for ECDSA --- src/pubkey.cpp | 260 +++++++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 233 insertions(+), 27 deletions(-) (limited to 'src/pubkey.cpp') diff --git a/src/pubkey.cpp b/src/pubkey.cpp index bdab137600..6ebb152c75 100644 --- a/src/pubkey.cpp +++ b/src/pubkey.cpp @@ -4,19 +4,184 @@ #include "pubkey.h" -#include "eccryptoverify.h" +#include +#include -#include "ecwrapper.h" +namespace +{ +/* Global secp256k1_context object used for verification. */ +secp256k1_context* secp256k1_context_verify = NULL; +} + +/** This function is taken from the libsecp256k1 distribution and implements + * DER parsing for ECDSA signatures, while supporting an arbitrary subset of + * format violations. + * + * Supported violations include negative integers, excessive padding, garbage + * at the end, and overly long length descriptors. This is safe to use in + * Bitcoin because since the activation of BIP66, signatures are verified to be + * strict DER before being passed to this module, and we know it supports all + * violations present in the blockchain before that point. + */ +static int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen) { + size_t rpos, rlen, spos, slen; + size_t pos = 0; + size_t lenbyte; + unsigned char tmpsig[64] = {0}; + int overflow = 0; + + /* Hack to initialize sig with a correctly-parsed but invalid signature. */ + secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig); + + /* Sequence tag byte */ + if (pos == inputlen || input[pos] != 0x30) { + return 0; + } + pos++; + + /* Sequence length bytes */ + if (pos == inputlen) { + return 0; + } + lenbyte = input[pos++]; + if (lenbyte & 0x80) { + lenbyte -= 0x80; + if (pos + lenbyte > inputlen) { + return 0; + } + pos += lenbyte; + } + + /* Integer tag byte for R */ + if (pos == inputlen || input[pos] != 0x02) { + return 0; + } + pos++; + + /* Integer length for R */ + if (pos == inputlen) { + return 0; + } + lenbyte = input[pos++]; + if (lenbyte & 0x80) { + lenbyte -= 0x80; + if (pos + lenbyte > inputlen) { + return 0; + } + while (lenbyte > 0 && input[pos] == 0) { + pos++; + lenbyte--; + } + if (lenbyte >= sizeof(size_t)) { + return 0; + } + rlen = 0; + while (lenbyte > 0) { + rlen = (rlen << 8) + input[pos]; + pos++; + lenbyte--; + } + } else { + rlen = lenbyte; + } + if (rlen > inputlen - pos) { + return 0; + } + rpos = pos; + pos += rlen; + + /* Integer tag byte for S */ + if (pos == inputlen || input[pos] != 0x02) { + return 0; + } + pos++; + + /* Integer length for S */ + if (pos == inputlen) { + return 0; + } + lenbyte = input[pos++]; + if (lenbyte & 0x80) { + lenbyte -= 0x80; + if (pos + lenbyte > inputlen) { + return 0; + } + while (lenbyte > 0 && input[pos] == 0) { + pos++; + lenbyte--; + } + if (lenbyte >= sizeof(size_t)) { + return 0; + } + slen = 0; + while (lenbyte > 0) { + slen = (slen << 8) + input[pos]; + pos++; + lenbyte--; + } + } else { + slen = lenbyte; + } + if (slen > inputlen - pos) { + return 0; + } + spos = pos; + pos += slen; + + /* Ignore leading zeroes in R */ + while (rlen > 0 && input[rpos] == 0) { + rlen--; + rpos++; + } + /* Copy R value */ + if (rlen > 32) { + overflow = 1; + } else { + memcpy(tmpsig + 32 - rlen, input + rpos, rlen); + } + + /* Ignore leading zeroes in S */ + while (slen > 0 && input[spos] == 0) { + slen--; + spos++; + } + /* Copy S value */ + if (slen > 32) { + overflow = 1; + } else { + memcpy(tmpsig + 64 - slen, input + spos, slen); + } + + if (!overflow) { + overflow = !secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig); + } + if (overflow) { + /* Overwrite the result again with a correctly-parsed but invalid + signature if parsing failed. */ + memset(tmpsig, 0, 64); + secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig); + } + return 1; +} bool CPubKey::Verify(const uint256 &hash, const std::vector& vchSig) const { if (!IsValid()) return false; - CECKey key; - if (!key.SetPubKey(begin(), size())) + secp256k1_pubkey pubkey; + secp256k1_ecdsa_signature sig; + if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size())) { return false; - if (!key.Verify(hash, vchSig)) + } + if (vchSig.size() == 0) { return false; - return true; + } + if (!ecdsa_signature_parse_der_lax(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) { + return false; + } + /* libsecp256k1's ECDSA verification requires lower-S signatures, which have + * not historically been enforced in Bitcoin, so normalize them first. */ + secp256k1_ecdsa_signature_normalize(secp256k1_context_verify, &sig, &sig); + return secp256k1_ecdsa_verify(secp256k1_context_verify, &sig, hash.begin(), &pubkey); } bool CPubKey::RecoverCompact(const uint256 &hash, const std::vector& vchSig) { @@ -24,33 +189,39 @@ bool CPubKey::RecoverCompact(const uint256 &hash, const std::vector pubkey; - key.GetPubKey(pubkey, fComp); - Set(pubkey.begin(), pubkey.end()); + } + if (!secp256k1_ecdsa_recover(secp256k1_context_verify, &pubkey, &sig, hash.begin())) { + return false; + } + unsigned char pub[65]; + size_t publen = 65; + secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, fComp ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED); + Set(pub, pub + publen); return true; } bool CPubKey::IsFullyValid() const { if (!IsValid()) return false; - CECKey key; - if (!key.SetPubKey(begin(), size())) - return false; - return true; + secp256k1_pubkey pubkey; + return secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size()); } bool CPubKey::Decompress() { if (!IsValid()) return false; - CECKey key; - if (!key.SetPubKey(begin(), size())) + secp256k1_pubkey pubkey; + if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size())) { return false; - std::vector pubkey; - key.GetPubKey(pubkey, false); - Set(pubkey.begin(), pubkey.end()); + } + unsigned char pub[65]; + size_t publen = 65; + secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, SECP256K1_EC_UNCOMPRESSED); + Set(pub, pub + publen); return true; } @@ -61,13 +232,18 @@ bool CPubKey::Derive(CPubKey& pubkeyChild, ChainCode &ccChild, unsigned int nChi unsigned char out[64]; BIP32Hash(cc, nChild, *begin(), begin()+1, out); memcpy(ccChild.begin(), out+32, 32); - CECKey key; - bool ret = key.SetPubKey(begin(), size()); - ret &= key.TweakPublic(out); - std::vector pubkey; - key.GetPubKey(pubkey, true); - pubkeyChild.Set(pubkey.begin(), pubkey.end()); - return ret; + secp256k1_pubkey pubkey; + if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size())) { + return false; + } + if (!secp256k1_ec_pubkey_tweak_add(secp256k1_context_verify, &pubkey, out)) { + return false; + } + unsigned char pub[33]; + size_t publen = 33; + secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, SECP256K1_EC_COMPRESSED); + pubkeyChild.Set(pub, pub + publen); + return true; } void CExtPubKey::Encode(unsigned char code[74]) const { @@ -95,3 +271,33 @@ bool CExtPubKey::Derive(CExtPubKey &out, unsigned int nChild) const { out.nChild = nChild; return pubkey.Derive(out.pubkey, out.chaincode, nChild, chaincode); } + +/* static */ bool CPubKey::CheckLowS(const std::vector& vchSig) { + secp256k1_ecdsa_signature sig; + if (!ecdsa_signature_parse_der_lax(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) { + return false; + } + return (!secp256k1_ecdsa_signature_normalize(secp256k1_context_verify, NULL, &sig)); +} + +/* static */ int ECCVerifyHandle::refcount = 0; + +ECCVerifyHandle::ECCVerifyHandle() +{ + if (refcount == 0) { + assert(secp256k1_context_verify == NULL); + secp256k1_context_verify = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY); + assert(secp256k1_context_verify != NULL); + } + refcount++; +} + +ECCVerifyHandle::~ECCVerifyHandle() +{ + refcount--; + if (refcount == 0) { + assert(secp256k1_context_verify != NULL); + secp256k1_context_destroy(secp256k1_context_verify); + secp256k1_context_verify = NULL; + } +} -- cgit v1.2.3