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# emsa2.cpp

    00001 // emsa2.cpp - written and placed in the public domain by Wei Dai
    00002
    00003 #include "pch.h"
    00004 #include "emsa2.h"
    00005
    00006 #ifndef CRYPTOPP_IMPORTS
    00007
    00008 NAMESPACE_BEGIN(CryptoPP)
    00009
    00010 void EMSA2Pad::ComputeMessageRepresentative(RandomNumberGenerator &rng,
    00011         const byte *recoverableMessage, size_t recoverableMessageLength,
    00012         HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,
    00013         byte *representative, size_t representativeBitLength) const
    00014 {
    00015         assert(representativeBitLength >= MinRepresentativeBitLength(hashIdentifier.second, hash.DigestSize()));
    00016
    00017         if (representativeBitLength % 8 != 7)
    00018                 throw PK_SignatureScheme::InvalidKeyLength("EMSA2: EMSA2 requires a key length that is a multiple of 8");
    00019
    00020         size_t digestSize = hash.DigestSize();
    00021         size_t representativeByteLength = BitsToBytes(representativeBitLength);
    00022
    00023         representative[0] = messageEmpty ? 0x4b : 0x6b;
    00024         memset(representative+1, 0xbb, representativeByteLength-digestSize-4);  // pad with 0xbb
    00025         byte *afterP2 = representative+representativeByteLength-digestSize-3;
    00026         afterP2[0] = 0xba;
    00027         hash.Final(afterP2+1);
    00028         representative[representativeByteLength-2] = *hashIdentifier.first;
    00029         representative[representativeByteLength-1] = 0xcc;
    00030 }
    00031
    00032 NAMESPACE_END
    00033
    00034 #endif