Modified source engine (2017) developed by valve and leaked in 2020. Not for commercial purporses
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// emsa2.cpp - originally written and placed in the public domain by Wei Dai
#include "pch.h"
#include "emsa2.h"
#ifndef CRYPTOPP_IMPORTS
NAMESPACE_BEGIN(CryptoPP)
// Inclusion based on DLL due to Clang, http://github.com/weidai11/cryptopp/issues/300
#ifndef CRYPTOPP_IS_DLL
template<> const byte EMSA2HashId<SHA1>::id = 0x33;
template<> const byte EMSA2HashId<SHA224>::id = 0x38;
template<> const byte EMSA2HashId<SHA256>::id = 0x34;
template<> const byte EMSA2HashId<SHA384>::id = 0x36;
template<> const byte EMSA2HashId<SHA512>::id = 0x35;
#endif
void EMSA2Pad::ComputeMessageRepresentative(RandomNumberGenerator& /*rng*/,
const byte* recoverableMessage, size_t recoverableMessageLength,
HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,
byte *representative, size_t representativeBitLength) const
{
CRYPTOPP_UNUSED(recoverableMessage), CRYPTOPP_UNUSED(recoverableMessageLength), CRYPTOPP_UNUSED(representativeBitLength);
CRYPTOPP_ASSERT(representativeBitLength >= MinRepresentativeBitLength(hashIdentifier.second, hash.DigestSize()));
if (representativeBitLength % 8 != 7)
throw PK_SignatureScheme::InvalidKeyLength("EMSA2: EMSA2 requires a key length that is a multiple of 8");
size_t digestSize = hash.DigestSize();
size_t representativeByteLength = BitsToBytes(representativeBitLength);
representative[0] = messageEmpty ? 0x4b : 0x6b;
memset(representative+1, 0xbb, representativeByteLength-digestSize-4); // pad with 0xbb
byte *afterP2 = representative+representativeByteLength-digestSize-3;
afterP2[0] = 0xba;
hash.Final(afterP2+1);
representative[representativeByteLength-2] = *hashIdentifier.first;
representative[representativeByteLength-1] = 0xcc;
}
NAMESPACE_END
#endif