AaltoTLS.RecordLayer.RecordHandler.TransformRecordBytes C# (CSharp) Method

        private static byte[] TransformRecordBytes(BulkCipherAlgorithmType cipherType, ICryptoTransform transform, byte[] input)
        {
            if (cipherType != BulkCipherAlgorithmType.AEAD) {
                // In case of non-AEAD cipher algorithm, check that data matches block size
                if (input.Length % transform.InputBlockSize != 0) {
                    throw new Exception("Input data size doesn't match block size");
                }
            }

            int blockCount = input.Length / transform.InputBlockSize;
            if (cipherType == BulkCipherAlgorithmType.AEAD) {
                // Make sure there is enough data at TransformFinalBlock, because
                // decryption requires that the authentication tag is present
                if (blockCount > 0) {
                    blockCount--;
                }
            }

            byte[] output = new byte[blockCount * transform.OutputBlockSize];
            if (transform.CanTransformMultipleBlocks) {
                transform.TransformBlock(input, 0, blockCount*transform.InputBlockSize, output, 0);
            } else {
                for (int i=0; i<blockCount; i++) {
                    transform.TransformBlock(input, i*transform.InputBlockSize,
                                             transform.InputBlockSize,
                                             output, i*transform.OutputBlockSize);
                }
            }

            if (cipherType == BulkCipherAlgorithmType.AEAD) {
                int currentPosition = blockCount*transform.InputBlockSize;

                // Transfer the last block when encrypting or authentication tag when decrypting
                byte[] finalBytes = transform.TransformFinalBlock(input, currentPosition, input.Length-currentPosition);
                if (finalBytes == null) {
                    return null;
                } else if (finalBytes.Length > 0) {
                    byte[] finalOutput = new byte[output.Length + finalBytes.Length];
                    Buffer.BlockCopy(output, 0, finalOutput, 0, output.Length);
                    Buffer.BlockCopy(finalBytes, 0, finalOutput, output.Length, finalBytes.Length);
                    output = finalOutput;
                }
            }

            return output;
        }