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// 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
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