Org.BouncyCastle.Crypto.Engines.IesEngine.DecryptBlock C# (CSharp) Метод

        private byte[] DecryptBlock(
            byte[]  in_enc,
            int     inOff,
            int     inLen,
            byte[]  z)
        {
            byte[]          M = null;
            KeyParameter    macKey = null;
            KdfParameters   kParam = new KdfParameters(z, param.GetDerivationV());
            int             macKeySize = param.MacKeySize;

            kdf.Init(kParam);

            inLen -= mac.GetMacSize();

            if (cipher == null)     // stream mode
            {
                byte[] Buffer = GenerateKdfBytes(kParam, inLen + (macKeySize / 8));

                M = new byte[inLen];

                for (int i = 0; i != inLen; i++)
                {
                    M[i] = (byte)(in_enc[inOff + i] ^ Buffer[i]);
                }

                macKey = new KeyParameter(Buffer, inLen, (macKeySize / 8));
            }
            else
            {
                int cipherKeySize = ((IesWithCipherParameters)param).CipherKeySize;
                byte[] Buffer = GenerateKdfBytes(kParam, (cipherKeySize / 8) + (macKeySize / 8));

                cipher.Init(false, new KeyParameter(Buffer, 0, (cipherKeySize / 8)));

                M = cipher.DoFinal(in_enc, inOff, inLen);

                macKey = new KeyParameter(Buffer, (cipherKeySize / 8), (macKeySize / 8));
            }

            byte[] macIV = param.GetEncodingV();

            mac.Init(macKey);
            mac.BlockUpdate(in_enc, inOff, inLen);
            mac.BlockUpdate(macIV, 0, macIV.Length);
            mac.DoFinal(macBuf, 0);

            inOff += inLen;

            for (int t = 0; t < macBuf.Length; t++)
            {
                if (macBuf[t] != in_enc[inOff + t])
                {
                    throw (new InvalidCipherTextException("IMac codes failed to equal."));
                }
            }

            return M;
        }