pssr.cpp

// pssr.cpp - originally written and placed in the public domain by Wei Dai
 
#include "pch.h"
#include "pssr.h"
#include "emsa2.h"
#include "ripemd.h"
#include "whrlpool.h"
#include "misc.h"
 
#include <functional>
 
NAMESPACE_BEGIN(CryptoPP)
 
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
{
    CRYPTOPP_UNUSED(rng), CRYPTOPP_UNUSED(recoverableMessage), CRYPTOPP_UNUSED(recoverableMessageLength);
    CRYPTOPP_UNUSED(messageEmpty), CRYPTOPP_UNUSED(hashIdentifier);
    CRYPTOPP_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;
    if (recoverableMessage && recoverableMessageLength)
        xorbuf(xorStart + 1, recoverableMessage, recoverableMessageLength);
    xorbuf(xorStart + 1 + recoverableMessageLength, salt, salt.size());
    if (hashIdentifier.first && hashIdentifier.second)
    {
        std::memcpy(representative + representativeByteLength - u, hashIdentifier.first, hashIdentifier.second);
        representative[representativeByteLength - 1] = 0xcc;
    }
    else
    {
        representative[representativeByteLength - 1] = 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
{
    CRYPTOPP_UNUSED(recoverableMessage), CRYPTOPP_UNUSED(messageEmpty), CRYPTOPP_UNUSED(hashIdentifier);
    CRYPTOPP_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;
 
    if (hashIdentifier.first && hashIdentifier.second)
        valid = VerifyBufsEqual(representative + representativeByteLength - u, hashIdentifier.first, hashIdentifier.second) && 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 = FindIfNot(representative, salt-1, byte(0));
    recoverableMessageLength = salt-M-1;
    if (*M == 0x01 &&
       (size_t)(M - representative - (representativeBitLength % 8 != 0)) >= MinPadLen(digestSize) &&
       recoverableMessageLength <= MaxRecoverableLength(representativeBitLength, hashIdentifier.second, digestSize))
    {
        if (recoverableMessage)
            std::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