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Differential D1565 Diff 4315 src/script/sigencoding.cpp

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src/script/sigencoding.cpp

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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2016 The Bitcoin Core developers
// Copyright (c) 2017-2018 The Bitcoin developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include "sigencoding.h"
#include "pubkey.h"
#include "script_flags.h"
/**
* A canonical signature exists of: <30> <total len> <02> <len R> <R> <02> <len
* S> <S> <hashtype>, where R and S are not negative (their first byte has its
* highest bit not set), and not excessively padded (do not start with a 0 byte,
* unless an otherwise negative number follows, in which case a single 0 byte is
* necessary and even required).
*
* See https://bitcointalk.org/index.php?topic=8392.msg127623#msg127623
*
* This function is consensus-critical since BIP66.
*/
static bool IsValidSignatureEncoding(const valtype &sig) {
// Format: 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S]
// [sighash]
// * total-length: 1-byte length descriptor of everything that follows,
// excluding the sighash byte.
// * R-length: 1-byte length descriptor of the R value that follows.
// * R: arbitrary-length big-endian encoded R value. It must use the
// shortest possible encoding for a positive integers (which means no null
// bytes at the start, except a single one when the next byte has its
// highest bit set).
// * S-length: 1-byte length descriptor of the S value that follows.
// * S: arbitrary-length big-endian encoded S value. The same rules apply.
// * sighash: 1-byte value indicating what data is hashed (not part of the
// DER signature)
// Minimum and maximum size constraints.
if (sig.size() < 9) return false;
if (sig.size() > 73) return false;
// A signature is of type 0x30 (compound).
if (sig[0] != 0x30) return false;
// Make sure the length covers the entire signature.
if (sig[1] != sig.size() - 3) return false;
// Extract the length of the R element.
unsigned int lenR = sig[3];
// Make sure the length of the S element is still inside the signature.
if (5 + lenR >= sig.size()) return false;
// Extract the length of the S element.
unsigned int lenS = sig[5 + lenR];
// Verify that the length of the signature matches the sum of the length
// of the elements.
if ((size_t)(lenR + lenS + 7) != sig.size()) return false;
// Check whether the R element is an integer.
if (sig[2] != 0x02) return false;
// Zero-length integers are not allowed for R.
if (lenR == 0) return false;
// Negative numbers are not allowed for R.
if (sig[4] & 0x80) return false;
// Null bytes at the start of R are not allowed, unless R would otherwise be
// interpreted as a negative number.
if (lenR > 1 && (sig[4] == 0x00) && !(sig[5] & 0x80)) return false;
// Check whether the S element is an integer.
if (sig[lenR + 4] != 0x02) return false;
// Zero-length integers are not allowed for S.
if (lenS == 0) return false;
// Negative numbers are not allowed for S.
if (sig[lenR + 6] & 0x80) return false;
// Null bytes at the start of S are not allowed, unless S would otherwise be
// interpreted as a negative number.
if (lenS > 1 && (sig[lenR + 6] == 0x00) && !(sig[lenR + 7] & 0x80)) {
return false;
}
return true;
}
static bool IsLowDERSignature(const valtype &vchSig, ScriptError *serror) {
if (!IsValidSignatureEncoding(vchSig)) {
return set_error(serror, SCRIPT_ERR_SIG_DER);
}
std::vector<uint8_t> vchSigCopy(vchSig.begin(),
vchSig.begin() + vchSig.size() - 1);
if (!CPubKey::CheckLowS(vchSigCopy)) {
return set_error(serror, SCRIPT_ERR_SIG_HIGH_S);
}
return true;
}
bool CheckSignatureEncoding(const valtype &vchSig, uint32_t flags,
ScriptError *serror) {
// Empty signature. Not strictly DER encoded, but allowed to provide a
// compact way to provide an invalid signature for use with CHECK(MULTI)SIG
if (vchSig.size() == 0) {
return true;
}
if ((flags & (SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_LOW_S |
SCRIPT_VERIFY_STRICTENC)) != 0 &&
!IsValidSignatureEncoding(vchSig)) {
return set_error(serror, SCRIPT_ERR_SIG_DER);
}
if ((flags & SCRIPT_VERIFY_LOW_S) != 0 &&
!IsLowDERSignature(vchSig, serror)) {
// serror is set
return false;
}
if ((flags & SCRIPT_VERIFY_STRICTENC) != 0) {
if (!GetHashType(vchSig).isDefined()) {
return set_error(serror, SCRIPT_ERR_SIG_HASHTYPE);
}
bool usesForkId = GetHashType(vchSig).hasForkId();
bool forkIdEnabled = flags & SCRIPT_ENABLE_SIGHASH_FORKID;
if (!forkIdEnabled && usesForkId) {
return set_error(serror, SCRIPT_ERR_ILLEGAL_FORKID);
}
if (forkIdEnabled && !usesForkId) {
return set_error(serror, SCRIPT_ERR_MUST_USE_FORKID);
}
}
return true;
}
static bool IsCompressedOrUncompressedPubKey(const valtype &vchPubKey) {
if (vchPubKey.size() < 33) {
// Non-canonical public key: too short
return false;
}
if (vchPubKey[0] == 0x04) {
if (vchPubKey.size() != 65) {
// Non-canonical public key: invalid length for uncompressed key
return false;
}
} else if (vchPubKey[0] == 0x02 || vchPubKey[0] == 0x03) {
if (vchPubKey.size() != 33) {
// Non-canonical public key: invalid length for compressed key
return false;
}
} else {
// Non-canonical public key: neither compressed nor uncompressed
return false;
}
return true;
}
static bool IsCompressedPubKey(const valtype &vchPubKey) {
if (vchPubKey.size() != 33) {
// Non-canonical public key: invalid length for compressed key
return false;
}
if (vchPubKey[0] != 0x02 && vchPubKey[0] != 0x03) {
// Non-canonical public key: invalid prefix for compressed key
return false;
}
return true;
}
bool CheckPubKeyEncoding(const valtype &vchPubKey, uint32_t flags,
ScriptError *serror) {
if ((flags & SCRIPT_VERIFY_STRICTENC) != 0 &&
!IsCompressedOrUncompressedPubKey(vchPubKey)) {
return set_error(serror, SCRIPT_ERR_PUBKEYTYPE);
}
// Only compressed keys are accepted when
// SCRIPT_VERIFY_COMPRESSED_PUBKEYTYPE is enabled.
if ((flags & SCRIPT_VERIFY_COMPRESSED_PUBKEYTYPE) &&
!IsCompressedPubKey(vchPubKey)) {
return set_error(serror, SCRIPT_ERR_NONCOMPRESSED_PUBKEY);
}
return true;
}