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36 lines
1.2 KiB
C++
36 lines
1.2 KiB
C++
// emsa2.cpp - written and placed in the public domain by Wei Dai
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#include "pch.h"
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#include "emsa2.h"
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#include "trap.h"
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#ifndef CRYPTOPP_IMPORTS
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NAMESPACE_BEGIN(CryptoPP)
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void EMSA2Pad::ComputeMessageRepresentative(RandomNumberGenerator &rng,
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const byte *recoverableMessage, size_t recoverableMessageLength,
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HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,
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byte *representative, size_t representativeBitLength) const
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{
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CRYPTOPP_ASSERT(representativeBitLength >= MinRepresentativeBitLength(hashIdentifier.second, hash.DigestSize()));
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if (representativeBitLength % 8 != 7)
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throw PK_SignatureScheme::InvalidKeyLength("EMSA2: EMSA2 requires a key length that is a multiple of 8");
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size_t digestSize = hash.DigestSize();
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size_t representativeByteLength = BitsToBytes(representativeBitLength);
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representative[0] = messageEmpty ? 0x4b : 0x6b;
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memset(representative+1, 0xbb, representativeByteLength-digestSize-4); // pad with 0xbb
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byte *afterP2 = representative+representativeByteLength-digestSize-3;
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afterP2[0] = 0xba;
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hash.Final(afterP2+1);
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representative[representativeByteLength-2] = *hashIdentifier.first;
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representative[representativeByteLength-1] = 0xcc;
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}
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NAMESPACE_END
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#endif
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