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# oaep.cpp

    00001 // oaep.cpp - written and placed in the public domain by Wei Dai
    00002
    00003 #include "pch.h"
    00004
    00005 #ifndef CRYPTOPP_IMPORTS
    00006
    00007 #include "oaep.h"
    00008 #include <functional>
    00009
    00010 NAMESPACE_BEGIN(CryptoPP)
    00011
    00012 // ********************************************************
    00013
    00014 size_t OAEP_Base::MaxUnpaddedLength(size_t paddedLength) const
    00015 {
    00016         return SaturatingSubtract(paddedLength/8, 1+2*DigestSize());
    00017 }
    00018
    00019 void OAEP_Base::Pad(RandomNumberGenerator &rng, const byte *input, size_t inputLength, byte *oaepBlock, size_t oaepBlockLen, const NameValuePairs &parameters) const
    00020 {
    00021         assert (inputLength <= MaxUnpaddedLength(oaepBlockLen));
    00022
    00023         // convert from bit length to byte length
    00024         if (oaepBlockLen % 8 != 0)
    00025         {
    00026                 oaepBlock[0] = 0;
    00027                 oaepBlock++;
    00028         }
    00029         oaepBlockLen /= 8;
    00030
    00031         std::auto_ptr<HashTransformation> pHash(NewHash());
    00032         const size_t hLen = pHash->DigestSize();
    00033         const size_t seedLen = hLen, dbLen = oaepBlockLen-seedLen;
    00034         byte *const maskedSeed = oaepBlock;
    00035         byte *const maskedDB = oaepBlock+seedLen;
    00036
    00037         ConstByteArrayParameter encodingParameters;
    00038         parameters.GetValue(Name::EncodingParameters(), encodingParameters);
    00039
    00040         // DB = pHash || 00 ... || 01 || M
    00041         pHash->CalculateDigest(maskedDB, encodingParameters.begin(), encodingParameters.size());
    00042         memset(maskedDB+hLen, 0, dbLen-hLen-inputLength-1);
    00043         maskedDB[dbLen-inputLength-1] = 0x01;
    00044         memcpy(maskedDB+dbLen-inputLength, input, inputLength);
    00045
    00046         rng.GenerateBlock(maskedSeed, seedLen);
    00047         std::auto_ptr<MaskGeneratingFunction> pMGF(NewMGF());
    00048         pMGF->GenerateAndMask(*pHash, maskedDB, dbLen, maskedSeed, seedLen);
    00049         pMGF->GenerateAndMask(*pHash, maskedSeed, seedLen, maskedDB, dbLen);
    00050 }
    00051
    00052 DecodingResult OAEP_Base::Unpad(const byte *oaepBlock, size_t oaepBlockLen, byte *output, const NameValuePairs &parameters) const
    00053 {
    00054         bool invalid = false;
    00055
    00056         // convert from bit length to byte length
    00057         if (oaepBlockLen % 8 != 0)
    00058         {
    00059                 invalid = (oaepBlock[0] != 0) || invalid;
    00060                 oaepBlock++;
    00061         }
    00062         oaepBlockLen /= 8;
    00063
    00064         std::auto_ptr<HashTransformation> pHash(NewHash());
    00065         const size_t hLen = pHash->DigestSize();
    00066         const size_t seedLen = hLen, dbLen = oaepBlockLen-seedLen;
    00067
    00068         invalid = (oaepBlockLen < 2*hLen+1) || invalid;
    00069
    00070         SecByteBlock t(oaepBlock, oaepBlockLen);
    00071         byte *const maskedSeed = t;
    00072         byte *const maskedDB = t+seedLen;
    00073
    00074         std::auto_ptr<MaskGeneratingFunction> pMGF(NewMGF());
    00075         pMGF->GenerateAndMask(*pHash, maskedSeed, seedLen, maskedDB, dbLen);
    00076         pMGF->GenerateAndMask(*pHash, maskedDB, dbLen, maskedSeed, seedLen);
    00077
    00078         ConstByteArrayParameter encodingParameters;
    00079         parameters.GetValue(Name::EncodingParameters(), encodingParameters);
    00080
    00081         // DB = pHash' || 00 ... || 01 || M
    00082         byte *M = std::find(maskedDB+hLen, maskedDB+dbLen, 0x01);
    00083         invalid = (M == maskedDB+dbLen) || invalid;
    00084         invalid = (std::find_if(maskedDB+hLen, M, std::bind2nd(std::not_equal_to<byte>(), 0)) != M) || invalid;
    00085         invalid = !pHash->VerifyDigest(maskedDB, encodingParameters.begin(), encodingParameters.size()) || invalid;
    00086
    00087         if (invalid)
    00088                 return DecodingResult();
    00089
    00090         M++;
    00091         memcpy(output, M, maskedDB+dbLen-M);
    00092         return DecodingResult(maskedDB+dbLen-M);
    00093 }
    00094
    00095 NAMESPACE_END
    00096
    00097 #endif