emsa2.cpp

// 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;
    std::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