~zooko/cryptopp/trunk

// emsa2.cpp - written and placed in the public domain by Wei Dai

 

#include "pch.h"

#include "emsa2.h"

 

#ifndef CRYPTOPP_IMPORTS

 

NAMESPACE_BEGIN(CryptoPP)

 

void EMSA2Pad::ComputeMessageRepresentative(RandomNumberGenerator &rng, 

        const byte *recoverableMessage, size_t recoverableMessageLength,

        HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,

        byte *representative, size_t representativeBitLength) const

{

        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