oaep.cpp

// oaep.cpp - originally written and placed in the public domain by Wei Dai

#include "pch.h"

#ifndef CRYPTOPP_IMPORTS

#include "oaep.h"
#include "stdcpp.h"
#include "smartptr.h"

NAMESPACE_BEGIN(CryptoPP)

// ********************************************************

size_t OAEP_Base::MaxUnpaddedLength(size_t paddedLength) const
{
    return SaturatingSubtract(paddedLength/8, 1+2*DigestSize());
}

void OAEP_Base::Pad(RandomNumberGenerator &rng, const byte *input, size_t inputLength, byte *oaepBlock, size_t oaepBlockLen, const NameValuePairs &parameters) const
{
    CRYPTOPP_ASSERT (inputLength <= MaxUnpaddedLength(oaepBlockLen));

    // convert from bit length to byte length
    if (oaepBlockLen % 8 != 0)
    {
        oaepBlock[0] = 0;
        oaepBlock++;
    }
    oaepBlockLen /= 8;

    member_ptr<HashTransformation> pHash(NewHash());
    const size_t hLen = pHash->DigestSize();
    const size_t seedLen = hLen, dbLen = oaepBlockLen-seedLen;
    byte *const maskedSeed = oaepBlock;
    byte *const maskedDB = oaepBlock+seedLen;

    ConstByteArrayParameter encodingParameters;
    parameters.GetValue(Name::EncodingParameters(), encodingParameters);

    // DB = pHash || 00 ... || 01 || M
    pHash->CalculateDigest(maskedDB, encodingParameters.begin(), encodingParameters.size());
    memset(maskedDB+hLen, 0, dbLen-hLen-inputLength-1);
    maskedDB[dbLen-inputLength-1] = 0x01;
    memcpy(maskedDB+dbLen-inputLength, input, inputLength);

    rng.GenerateBlock(maskedSeed, seedLen);
    member_ptr<MaskGeneratingFunction> pMGF(NewMGF());
    pMGF->GenerateAndMask(*pHash, maskedDB, dbLen, maskedSeed, seedLen);
    pMGF->GenerateAndMask(*pHash, maskedSeed, seedLen, maskedDB, dbLen);
}

DecodingResult OAEP_Base::Unpad(const byte *oaepBlock, size_t oaepBlockLen, byte *output, const NameValuePairs &parameters) const
{
    bool invalid = false;

    // convert from bit length to byte length
    if (oaepBlockLen % 8 != 0)
    {
        invalid = (oaepBlock[0] != 0) || invalid;
        oaepBlock++;
    }
    oaepBlockLen /= 8;

    member_ptr<HashTransformation> pHash(NewHash());
    const size_t hLen = pHash->DigestSize();
    const size_t seedLen = hLen, dbLen = oaepBlockLen-seedLen;

    invalid = (oaepBlockLen < 2*hLen+1) || invalid;

    SecByteBlock t(oaepBlock, oaepBlockLen);
    byte *const maskedSeed = t;
    byte *const maskedDB = t+seedLen;

    member_ptr<MaskGeneratingFunction> pMGF(NewMGF());
    pMGF->GenerateAndMask(*pHash, maskedSeed, seedLen, maskedDB, dbLen);
    pMGF->GenerateAndMask(*pHash, maskedDB, dbLen, maskedSeed, seedLen);

    ConstByteArrayParameter encodingParameters;
    parameters.GetValue(Name::EncodingParameters(), encodingParameters);

    // DB = pHash' || 00 ... || 01 || M
    byte *M = std::find(maskedDB+hLen, maskedDB+dbLen, 0x01);
    invalid = (M == maskedDB+dbLen) || invalid;
    invalid = (FindIfNot(maskedDB+hLen, M, byte(0)) != M) || invalid;
    invalid = !pHash->VerifyDigest(maskedDB, encodingParameters.begin(), encodingParameters.size()) || invalid;

    if (invalid)
        return DecodingResult();

    M++;
    memcpy(output, M, maskedDB+dbLen-M);
    return DecodingResult(maskedDB+dbLen-M);
}

NAMESPACE_END

#endif