Ejemplo n.º 1
0
        /// <summary>
        /// Mask generation function.
        /// </summary>
        /// <param name="seed">Seed</param>
        /// <param name="maskLen">Length of generated mask</param>
        /// <param name="hashLength">Length of the hash produced by the supplied hash provider</param>
        /// <param name="hashProvider">Hash provider to use in mask generation</param>
        /// <returns>Generated mask of specified length</returns>
        static internal byte[] OAEPMGF(byte[] seed, int maskLen, int hashLength, IHashProvider hashProvider)
        {
            byte[] result = new byte[maskLen];

            //Determine how many interations we have to do.  We'll be appending
            //m_hLen (hash length) bytes for every iteration, so the size of the generated byte array
            //will be m_hLen * iNum (number of iterations).
            int iNum = (int)Math.Floor(maskLen / hashLength) + 1;

            //Mask that will be truncated to create the final
            //resulting mask returned by this function.
            byte[] bytLongMask = new byte[(iNum * hashLength)];

            byte[] bytAppend = new byte[4];
            byte[] bytTmp    = null;
            int    iPadLen   = 0;

            byte[] bytSeedHash = new byte[hashLength];

            //Padded pseudorandom seed to be hashed.
            byte[] bytPadSeed = new byte[(seed.Length + 4)];
            seed.CopyTo(bytPadSeed, 0);

            for (int i = 0; i <= iNum - 1; i++)
            {
                //Convert the iterator to an Octet String byte array
                bytTmp = Mathematics.I2OSP(i, 4);

                //Calculate the needed padding zeros, and add
                //them to the resulting Array.  Result must be 4 bytes long.
                iPadLen = bytAppend.Length - bytTmp.Length;

                bytTmp.CopyTo(bytAppend, 0);

                //Hash the pseudorandom padded seed and append it to the
                //long version of the mask.
                bytAppend.CopyTo(bytPadSeed, seed.Length);
                bytSeedHash = hashProvider.ComputeHash(bytPadSeed);
                bytSeedHash.CopyTo(bytLongMask, i * hashLength);
            }

            //Copy the first maskLen bytes of bytLongMask to the result
            //and return the result.
            Array.Copy(bytLongMask, result, maskLen);

            return(result);
        }
Ejemplo n.º 2
0
        /// <summary>
        /// Removes padding that was added to the unencrypted data prior to encryption.
        /// </summary>
        /// <param name="dataBytes">Data to have padding removed</param>
        /// <param name="params">RSA Parameters used for padding computation</param>
        /// <returns>Unpadded message</returns>
        public byte[] DecodeMessage(byte[] dataBytes, RSAParameters @params)
        {
            m_k = @params.D.Length;
            if (!(m_k == dataBytes.Length))
            {
                throw new CryptographicException("Bad Data.");
            }

            //Length of the datablock
            int iDBLen = dataBytes.Length - m_hLen - 1;

            //Starting index for the data block.  This will be equal to m_hLen + 1.  The
            //index is zero based, and the dataBytes should start with a single leading byte,
            //plus the maskedSeed (equal to hash length m_hLen).
            int iDBidx = m_hLen + 1;

            //Single byte for leading byte
            byte bytY = 0;

            //Byte array matching the length of the hashing algorithm.
            //This array will hold the masked seed.
            byte[] maskedSeed = new byte[m_hLen];

            //Byte array matching the length of the following:
            //Private Exponent D minus Hash Length, minus 1 (for the leading byte)
            byte[] maskedDB = new byte[iDBLen];

            //Copy the leading byte
            bytY = dataBytes[0];

            //Copy the mask
            Array.Copy(dataBytes, 1, maskedSeed, 0, m_hLen);

            //Copy the data block
            Array.Copy(dataBytes, iDBidx, maskedDB, 0, iDBLen);

            //Reproduce the seed mask from the masked data block using the mask generation function
            byte[] seedMask = Mathematics.OAEPMGF(maskedDB, m_hLen, m_hLen, m_hashProvider);

            //Reproduce the Seed from the Seed Mask.
            byte[] seed = Mathematics.BitwiseXOR(maskedSeed, seedMask);

            //Reproduce the data block bask from the seed using the mask generation function
            byte[] dbMask = Mathematics.OAEPMGF(seed, m_k - m_hLen - 1, m_hLen, m_hashProvider);

            //Reproduce the data block from the masked data block and the seed
            byte[] dataBlock = Mathematics.BitwiseXOR(maskedDB, dbMask);

            //Pull the message from the data block.  First m_hLen bytes are the lHash,
            //followed by padding of 0x00's, followed by a single 0x01, then the message.
            //So we're going to start and index m_hLen and work forward.
            if (!(dataBlock[m_hLen] == 0x00))
            {
                throw new CryptographicException("Decryption Error.  Bad Data.");
            }

            //If we passed the 0x00 first byte test, iterate through the
            //data block and find the terminating character.
            int iDataIdx = 0;


            for (int i = m_hLen; i <= dataBlock.Length - 1; i++)
            {
                if (dataBlock[i] == 0x01)
                {
                    iDataIdx = i + 1;
                    break;
                }
            }

            //Now find the length of the data and copy it to a byte array.
            int iDataLen = dataBlock.Length - iDataIdx;

            byte[] result = new byte[iDataLen];
            Array.Copy(dataBlock, iDataIdx, result, 0, iDataLen);

            return(result);
        }
Ejemplo n.º 3
0
        /// <summary>
        /// Adds padding to the input data and returns the padded data.
        /// </summary>
        /// <param name="dataBytes">Data to be padded prior to encryption</param>
        /// <param name="params">RSA Parameters used for padding computation</param>
        /// <returns>Padded message</returns>
        public byte[] EncodeMessage(byte[] dataBytes, RSAParameters @params)
        {
            //Iterator
            int i = 0;

            //Get the size of the data to be encrypted
            m_mLen = dataBytes.Length;

            //Get the size of the public modulus (will serve as max length for cipher text)
            m_k = @params.N.Length;

            if (m_mLen > GetMaxMessageLength(@params))
            {
                throw new CryptographicException("Bad Data.");
            }

            //Generate the random octet seed (same length as hash)
            BigInteger biSeed = new BigInteger();

            biSeed.genRandomBits(m_hLen * 8, new Random());
            byte[] bytSeed = biSeed.getBytesRaw();

            //Make sure all of the bytes are greater than 0.
            for (i = 0; i <= bytSeed.Length - 1; i++)
            {
                if (bytSeed[i] == 0x00)
                {
                    //Replacing with the prime byte 17, no real reason...just picked at random.
                    bytSeed[i] = 0x17;
                }
            }

            //Mask the seed with MFG Function(SHA1 Hash)
            //This is the mask to be XOR'd with the DataBlock below.
            byte[] dbMask = Mathematics.OAEPMGF(bytSeed, m_k - m_hLen - 1, m_hLen, m_hashProvider);

            //Compute the length needed for PS (zero padding) and
            //fill a byte array to the computed length
            int psLen = GetMaxMessageLength(@params) - m_mLen;

            //Generate the SHA1 hash of an empty L (Label).  Label is not used for this
            //application of padding in the RSA specification.
            byte[] lHash = m_hashProvider.ComputeHash(System.Text.Encoding.UTF8.GetBytes(string.Empty.ToCharArray()));

            //Create a dataBlock which will later be masked.  The
            //data block includes the concatenated hash(L), PS,
            //a 0x01 byte, and the message.
            int dbLen = m_hLen + psLen + 1 + m_mLen;

            byte[] dataBlock = new byte[dbLen];

            int cPos = 0;

            //Current position

            //Add the L Hash to the data blcok
            for (i = 0; i <= lHash.Length - 1; i++)
            {
                dataBlock[cPos] = lHash[i];
                cPos           += 1;
            }

            //Add the zero padding
            for (i = 0; i <= psLen - 1; i++)
            {
                dataBlock[cPos] = 0x00;
                cPos           += 1;
            }

            //Add the 0x01 byte
            dataBlock[cPos] = 0x01;
            cPos           += 1;

            //Add the message
            for (i = 0; i <= dataBytes.Length - 1; i++)
            {
                dataBlock[cPos] = dataBytes[i];
                cPos           += 1;
            }

            //Create the masked data block.
            byte[] maskedDB = Mathematics.BitwiseXOR(dbMask, dataBlock);

            //Create the seed mask
            byte[] seedMask = Mathematics.OAEPMGF(maskedDB, m_hLen, m_hLen, m_hashProvider);

            //Create the masked seed
            byte[] maskedSeed = Mathematics.BitwiseXOR(bytSeed, seedMask);

            //Create the resulting cipher - starting with a 0 byte.
            byte[] result = new byte[@params.N.Length];
            result[0] = 0x00;

            //Add the masked seed
            maskedSeed.CopyTo(result, 1);

            //Add the masked data block
            maskedDB.CopyTo(result, maskedSeed.Length + 1);

            return(result);
        }