/* rsa.cpp                                
 *
 * Copyright (C) 2003 Sawtooth Consulting Ltd.
 *
 * This file is part of yaSSL.
 *
 * yaSSL is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * There are special exceptions to the terms and conditions of the GPL as it
 * is applied to yaSSL. View the full text of the exception in the file
 * FLOSS-EXCEPTIONS in the directory of this software distribution.
 *
 * yaSSL is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

/* based on Wei Dai's rsa.cpp from CryptoPP */

#include "runtime.hpp"
#include "rsa.hpp"
#include "asn.hpp"
#include "modarith.hpp"



namespace TaoCrypt {


Integer RSA_PublicKey::ApplyFunction(const Integer& x) const
{
    return a_exp_b_mod_c(x, e_, n_);
}


RSA_PublicKey::RSA_PublicKey(Source& source)
{
    Initialize(source);
}


void RSA_PublicKey::Initialize(Source& source)
{
    RSA_Public_Decoder decoder(source);
    decoder.Decode(*this);
}


Integer RSA_PrivateKey::CalculateInverse(RandomNumberGenerator& rng,
                                         const Integer& x) const
{
    ModularArithmetic modn(n_);

    Integer r(rng, Integer::One(), n_ - Integer::One());
    Integer re = modn.Exponentiate(r, e_);
    re = modn.Multiply(re, x);			// blind

    // here we follow the notation of PKCS #1 and let u=q inverse mod p
    // but in ModRoot, u=p inverse mod q, so we reverse the order of p and q

    Integer y = ModularRoot(re, dq_, dp_, q_, p_, u_);
    y = modn.Divide(y, r);				    // unblind
    assert(modn.Exponentiate(y, e_) == x);  // check
       
    return y;
}


RSA_PrivateKey::RSA_PrivateKey(Source& source)
{
    Initialize(source);
}


void RSA_PrivateKey::Initialize(Source& source)
{
    RSA_Private_Decoder decoder(source);
    decoder.Decode(*this);
}


void RSA_BlockType2::Pad(const byte *input, word32 inputLen, byte *pkcsBlock,
                         word32 pkcsBlockLen, RandomNumberGenerator& rng) const
{
    // convert from bit length to byte length
    if (pkcsBlockLen % 8 != 0)
    {
        pkcsBlock[0] = 0;
        pkcsBlock++;
    }
    pkcsBlockLen /= 8;

    pkcsBlock[0] = 2;  // block type 2

    // pad with non-zero random bytes
    word32 padLen = pkcsBlockLen - inputLen - 1;
    rng.GenerateBlock(&pkcsBlock[1], padLen);
    for (word32 i = 1; i < padLen; i++)
        if (pkcsBlock[i] == 0) pkcsBlock[i] = 0x01;
    
    pkcsBlock[pkcsBlockLen-inputLen-1] = 0;     // separator
    memcpy(pkcsBlock+pkcsBlockLen-inputLen, input, inputLen);
}

word32 RSA_BlockType2::UnPad(const byte *pkcsBlock, unsigned int pkcsBlockLen,
                           byte *output) const
{
    bool invalid = false;
    unsigned int maxOutputLen = SaturatingSubtract(pkcsBlockLen / 8, 10U);

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

    // Require block type 2.
    invalid = (pkcsBlock[0] != 2) || invalid;

    // skip past the padding until we find the separator
    unsigned i=1;
    while (i<pkcsBlockLen && pkcsBlock[i++]) { // null body
        }
    assert(i==pkcsBlockLen || pkcsBlock[i-1]==0);

    unsigned int outputLen = pkcsBlockLen - i;
    invalid = (outputLen > maxOutputLen) || invalid;

    if (invalid)
        return 0;

    memcpy (output, pkcsBlock+i, outputLen);
    return outputLen;
}


void RSA_BlockType1::Pad(const byte* input, word32 inputLen, byte* pkcsBlock,
                         word32 pkcsBlockLen, RandomNumberGenerator&) const
{
    // convert from bit length to byte length
    if (pkcsBlockLen % 8 != 0)
    {
        pkcsBlock[0] = 0;
        pkcsBlock++;
    }
    pkcsBlockLen /= 8;

    pkcsBlock[0] = 1;  // block type 1 for SSL

    // pad with 0xff bytes
    memset(&pkcsBlock[1], 0xFF, pkcsBlockLen - inputLen - 2);

    pkcsBlock[pkcsBlockLen-inputLen-1] = 0;     // separator
    memcpy(pkcsBlock+pkcsBlockLen-inputLen, input, inputLen);
}


word32 RSA_BlockType1::UnPad(const byte* pkcsBlock, word32 pkcsBlockLen,
                             byte* output) const
{
    bool invalid = false;
    unsigned int maxOutputLen = SaturatingSubtract(pkcsBlockLen / 8, 10U);

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

    // Require block type 1 for SSL.
    invalid = (pkcsBlock[0] != 1) || invalid;

    // skip past the padding until we find the separator
    unsigned i=1;
    while (i<pkcsBlockLen && pkcsBlock[i++]) { // null body
        }
    assert(i==pkcsBlockLen || pkcsBlock[i-1]==0);

    unsigned int outputLen = pkcsBlockLen - i;
    invalid = (outputLen > maxOutputLen) || invalid;

    if (invalid)
        return 0;

    memcpy(output, pkcsBlock+i, outputLen);
    return outputLen;
}


word32 SSL_Decrypt(const RSA_PublicKey& key, const byte* sig, byte* plain)
{
    PK_Lengths lengths(key.GetModulus());
   
    ByteBlock paddedBlock(BitsToBytes(lengths.PaddedBlockBitLength()));
    Integer x = key.ApplyFunction(Integer(sig,
                                          lengths.FixedCiphertextLength()));
    if (x.ByteCount() > paddedBlock.size())
        x = Integer::Zero();	
    x.Encode(paddedBlock.get_buffer(), paddedBlock.size());
    return RSA_BlockType1().UnPad(paddedBlock.get_buffer(),
                                  lengths.PaddedBlockBitLength(), plain);
}


} // namespace
