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// pssr.cpp - written and placed in the public domain by Wei Dai
#include "pch.h"
#include "pssr.h"
#include <functional>
NAMESPACE_BEGIN(CryptoPP)
// more in dll.cpp
template<> const byte EMSA2HashId<RIPEMD160>::id = 0x31;
template<> const byte EMSA2HashId<RIPEMD128>::id = 0x32;
template<> const byte EMSA2HashId<Whirlpool>::id = 0x37;
#ifndef CRYPTOPP_IMPORTS
size_t PSSR_MEM_Base::MinRepresentativeBitLength(size_t hashIdentifierLength, size_t digestLength) const
{
size_t saltLen = SaltLen(digestLength);
size_t minPadLen = MinPadLen(digestLength);
return 9 + 8*(minPadLen + saltLen + digestLength + hashIdentifierLength);
}
size_t PSSR_MEM_Base::MaxRecoverableLength(size_t representativeBitLength, size_t hashIdentifierLength, size_t digestLength) const
{
if (AllowRecovery())
return SaturatingSubtract(representativeBitLength, MinRepresentativeBitLength(hashIdentifierLength, digestLength)) / 8;
return 0;
}
bool PSSR_MEM_Base::IsProbabilistic() const
{
return SaltLen(1) > 0;
}
bool PSSR_MEM_Base::AllowNonrecoverablePart() const
{
return true;
}
bool PSSR_MEM_Base::RecoverablePartFirst() const
{
return false;
}
void PSSR_MEM_Base::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()));
const size_t u = hashIdentifier.second + 1;
const size_t representativeByteLength = BitsToBytes(representativeBitLength);
const size_t digestSize = hash.DigestSize();
const size_t saltSize = SaltLen(digestSize);
byte *const h = representative + representativeByteLength - u - digestSize;
SecByteBlock digest(digestSize), salt(saltSize);
hash.Final(digest);
rng.GenerateBlock(salt, saltSize);
// compute H = hash of M'
byte c[8];
PutWord(false, BIG_ENDIAN_ORDER, c, (word32)SafeRightShift<29>(recoverableMessageLength));
PutWord(false, BIG_ENDIAN_ORDER, c+4, word32(recoverableMessageLength << 3));
hash.Update(c, 8);
hash.Update(recoverableMessage, recoverableMessageLength);
hash.Update(digest, digestSize);
hash.Update(salt, saltSize);
hash.Final(h);
// compute representative
GetMGF().GenerateAndMask(hash, representative, representativeByteLength - u - digestSize, h, digestSize, false);
byte *xorStart = representative + representativeByteLength - u - digestSize - salt.size() - recoverableMessageLength - 1;
xorStart[0] ^= 1;
xorbuf(xorStart + 1, recoverableMessage, recoverableMessageLength);
xorbuf(xorStart + 1 + recoverableMessageLength, salt, salt.size());
memcpy(representative + representativeByteLength - u, hashIdentifier.first, hashIdentifier.second);
representative[representativeByteLength - 1] = hashIdentifier.second ? 0xcc : 0xbc;
if (representativeBitLength % 8 != 0)
representative[0] = (byte)Crop(representative[0], representativeBitLength % 8);
}
DecodingResult PSSR_MEM_Base::RecoverMessageFromRepresentative(
HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,
byte *representative, size_t representativeBitLength,
byte *recoverableMessage) const
{
assert(representativeBitLength >= MinRepresentativeBitLength(hashIdentifier.second, hash.DigestSize()));
const size_t u = hashIdentifier.second + 1;
const size_t representativeByteLength = BitsToBytes(representativeBitLength);
const size_t digestSize = hash.DigestSize();
const size_t saltSize = SaltLen(digestSize);
const byte *const h = representative + representativeByteLength - u - digestSize;
SecByteBlock digest(digestSize);
hash.Final(digest);
DecodingResult result(0);
bool &valid = result.isValidCoding;
size_t &recoverableMessageLength = result.messageLength;
valid = (representative[representativeByteLength - 1] == (hashIdentifier.second ? 0xcc : 0xbc)) && valid;
valid = (memcmp(representative + representativeByteLength - u, hashIdentifier.first, hashIdentifier.second) == 0) && valid;
GetMGF().GenerateAndMask(hash, representative, representativeByteLength - u - digestSize, h, digestSize);
if (representativeBitLength % 8 != 0)
representative[0] = (byte)Crop(representative[0], representativeBitLength % 8);
// extract salt and recoverableMessage from DB = 00 ... || 01 || M || salt
byte *salt = representative + representativeByteLength - u - digestSize - saltSize;
byte *M = std::find_if(representative, salt-1, std::bind2nd(std::not_equal_to<byte>(), 0));
recoverableMessageLength = salt-M-1;
if (*M == 0x01
&& (size_t)(M - representative - (representativeBitLength % 8 != 0)) >= MinPadLen(digestSize)
&& recoverableMessageLength <= MaxRecoverableLength(representativeBitLength, hashIdentifier.second, digestSize))
{
memcpy(recoverableMessage, M+1, recoverableMessageLength);
}
else
{
recoverableMessageLength = 0;
valid = false;
}
// verify H = hash of M'
byte c[8];
PutWord(false, BIG_ENDIAN_ORDER, c, (word32)SafeRightShift<29>(recoverableMessageLength));
PutWord(false, BIG_ENDIAN_ORDER, c+4, word32(recoverableMessageLength << 3));
hash.Update(c, 8);
hash.Update(recoverableMessage, recoverableMessageLength);
hash.Update(digest, digestSize);
hash.Update(salt, saltSize);
valid = hash.Verify(h) && valid;
if (!AllowRecovery() && valid && recoverableMessageLength != 0)
{throw NotImplemented("PSSR_MEM: message recovery disabled");}
return result;
}
#endif
NAMESPACE_END
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