// Transform an input block into an output block.
public static int TransformBlock(CryptoAPITransform transform,
byte[] inputBuffer, int inputOffset,
int inputCount, byte[] outputBuffer,
int outputOffset)
{
int blockSize = transform.blockSize;
byte[] iv = transform.iv;
IntPtr state = transform.state;
int offset = outputOffset;
byte[] tempBuffer = transform.tempBuffer;
int tempSize = transform.tempSize;
int index;
// Process all of the data in the input. We need to keep
// the last two blocks for the finalization process.
while (inputCount >= blockSize)
{
// If the temporary buffer is full, then flush a block
// through the cipher in CBC mode.
if (tempSize > blockSize)
{
// Decrypt the ciphertext block and XOR with the IV.
CryptoMethods.Decrypt(state, tempBuffer, blockSize,
tempBuffer, 0);
for (index = blockSize - 1; index >= 0; --index)
{
tempBuffer[index] ^= iv[index];
}
// Copy the original ciphertext to the IV.
Array.Copy(tempBuffer, blockSize, iv, 0, blockSize);
// Copy the plaintext into place.
Array.Copy(tempBuffer, 0, outputBuffer,
offset, blockSize);
// Advance to the next output block.
offset += blockSize;
// Shift the second block down to the first position.
Array.Copy(tempBuffer, blockSize * 2,
tempBuffer, blockSize, blockSize);
tempSize -= blockSize;
}
// Copy the next block into the temporary buffer.
Array.Copy(inputBuffer, inputOffset,
tempBuffer, tempSize + blockSize, blockSize);
inputOffset += blockSize;
inputCount -= blockSize;
tempSize += blockSize;
}
transform.tempSize = tempSize;
// Finished.
return(offset - outputOffset);
}
// Transform an input block into an output block.
public static int TransformBlock(CryptoAPITransform transform,
byte[] inputBuffer, int inputOffset,
int inputCount, byte[] outputBuffer,
int outputOffset)
{
int blockSize = transform.blockSize;
byte[] iv = transform.iv;
IntPtr state = transform.state;
byte[] tempBuffer = transform.tempBuffer;
int offset = outputOffset;
int index;
bool needPadding = (transform.padding != PaddingMode.None);
// Process a left-over block from last time.
if (transform.tempSize > 0 && inputCount > 0)
{
// Decrypt the ciphertext to get the plaintext.
CryptoMethods.Decrypt(state, tempBuffer, 0,
outputBuffer, offset);
// Advance to the next block and clear the temporary block.
offset += blockSize;
transform.tempSize = 0;
for (index = blockSize - 1; index >= 0; --index)
{
tempBuffer[index] = (byte)0x00;
}
}
// Process all of the blocks in the input, minus one.
// If we don't need padding, then process all of the blocks.
while ((needPadding && inputCount > blockSize) ||
(!needPadding && inputCount >= blockSize))
{
// Decrypt the ciphertext to get the plaintext.
CryptoMethods.Decrypt(state, inputBuffer, inputOffset,
outputBuffer, offset);
// Advance to the next block.
inputOffset += blockSize;
inputCount -= blockSize;
offset += blockSize;
}
// Save the last block for next time.
if (needPadding && inputCount > 0)
{
Array.Copy(inputBuffer, inputOffset,
tempBuffer, 0, inputCount);
transform.tempSize = inputCount;
}
// Finished.
return(offset - outputOffset);
}
// Transform the final input block.
public static byte[] TransformFinalBlock(CryptoAPITransform transform,
byte[] inputBuffer,
int inputOffset,
int inputCount)
{
int blockSize = transform.blockSize;
byte[] iv = transform.iv;
IntPtr state = transform.state;
int offset;
byte[] tempBuffer = transform.tempBuffer;
byte[] outputBuffer;
int tempSize;
int index;
// Allocate the output buffer.
outputBuffer = new byte [inputCount + transform.tempSize];
// Process as many full blocks as possible.
index = inputCount - (inputCount % blockSize);
offset = TransformBlock(transform, inputBuffer,
inputOffset, index,
outputBuffer, 0);
inputOffset += index;
inputCount -= index;
// Flush the first block if we need the extra space.
tempSize = transform.tempSize;
if (tempSize > blockSize && inputCount > 0)
{
// Decrypt the ciphertext block and XOR with the IV.
CryptoMethods.Decrypt(state, tempBuffer, blockSize,
tempBuffer, 0);
for (index = blockSize - 1; index >= 0; --index)
{
tempBuffer[index] ^= iv[index];
}
// Copy the original ciphertext to the IV.
Array.Copy(tempBuffer, blockSize, iv, 0, blockSize);
// Copy the plaintext into place.
Array.Copy(tempBuffer, 0, outputBuffer,
offset, blockSize);
// Advance to the next output block.
offset += blockSize;
// Shift the second block down to the first position.
Array.Copy(tempBuffer, blockSize * 2,
tempBuffer, blockSize, blockSize);
tempSize -= blockSize;
}
// Copy the remainder of the data into the temporary buffer.
Array.Copy(inputBuffer, inputOffset,
tempBuffer, tempSize + blockSize, inputCount);
tempSize += inputCount;
// "Applied Cryptography" describes Cipher Text Stealing
// as taking two blocks to generate the short end-point.
// If we less than one block, then use CFB instead.
if (tempSize < blockSize)
{
// Decrypt the single block in CFB mode.
CryptoMethods.Encrypt(transform.state2, iv, 0, iv, 0);
for (index = 0; index < tempSize; ++index)
{
outputBuffer[offset + index] =
(byte)(iv[index] ^ tempBuffer[index + blockSize]);
}
}
else
{
// Decrypt the second last ciphertext block.
CryptoMethods.Decrypt(state, tempBuffer, blockSize,
tempBuffer, blockSize);
// Rebuild the ciphertext for the last block.
for (index = inputCount; index < blockSize; ++index)
{
tempBuffer[blockSize * 2 + index] =
tempBuffer[blockSize + index];
}
// Get the last plaintext block from the second
// last ciphertext block.
for (index = inputCount - 1; index >= 0; --index)
{
outputBuffer[offset + blockSize + index] =
(byte)(tempBuffer[blockSize + index] ^
tempBuffer[blockSize * 2 + index]);
}
// Decrypt the last ciphertext block that we rebuilt.
CryptoMethods.Decrypt(state, tempBuffer, blockSize * 2,
tempBuffer, 0);
// XOR the block with the IV to get the second
// last plaintext block.
for (index = blockSize - 1; index >= 0; --index)
{
outputBuffer[offset + index] =
(byte)(iv[index] ^ tempBuffer[index]);
}
}
// Finished.
return(outputBuffer);
}
// Transform the final input block.
public static byte[] TransformFinalBlock(CryptoAPITransform transform,
byte[] inputBuffer,
int inputOffset,
int inputCount)
{
int blockSize = transform.blockSize;
IntPtr state = transform.state;
byte[] tempBuffer = transform.tempBuffer;
byte[] outputBuffer;
int offset, index, pad;
// Allocate a temporary output buffer.
outputBuffer = new byte [inputCount + blockSize];
// Push the remaining bytes through the decryptor. The
// final block will end up in "transform.tempBuffer".
offset = TransformBlock(transform, inputBuffer, inputOffset,
inputCount, outputBuffer, 0);
// Decrypt the final block in "tempBuffer".
if (transform.tempSize > 0)
{
// Decrypt the ciphertext to get the plaintext.
CryptoMethods.Decrypt(state, tempBuffer, 0,
tempBuffer, 0);
// Remove padding.
if (transform.padding == PaddingMode.PKCS7)
{
// Use PKCS #7 padding.
pad = tempBuffer[blockSize - 1];
if (pad == 0 || pad > blockSize)
{
pad = blockSize;
}
Array.Copy(tempBuffer, 0, outputBuffer,
offset, blockSize - pad);
offset += blockSize - pad;
pad = 0;
}
else if (transform.padding == PaddingMode.Zeros)
{
// Strip zeroes from the end of the block.
index = blockSize;
while (index > 0 && tempBuffer[index - 1] == 0)
{
--index;
}
Array.Copy(tempBuffer, 0, outputBuffer,
offset, index);
offset += index;
}
else
{
// No padding, so return the whole block.
Array.Copy(tempBuffer, 0, outputBuffer,
offset, blockSize);
offset += blockSize;
}
}
// Reduce the output buffer size to the final length.
if (offset != outputBuffer.Length)
{
byte[] newout = new byte [offset];
if (offset != 0)
{
Array.Copy(outputBuffer, 0, newout, 0, offset);
}
Array.Clear(outputBuffer, 0, outputBuffer.Length);
outputBuffer = newout;
}
// Finished.
return(outputBuffer);
}
// Transform an input block into an output block.
public static int TransformBlock(CryptoAPITransform transform,
byte[] inputBuffer, int inputOffset,
int inputCount, byte[] outputBuffer,
int outputOffset)
{
int blockSize = transform.blockSize;
byte[] iv = transform.iv;
IntPtr state = transform.state;
byte[] tempBuffer = transform.tempBuffer;
int offset = outputOffset;
int index;
// Process a left-over block from last time.
if (transform.tempSize > 0 && inputCount > 0)
{
// Decrypt the ciphertext to get the plaintext
// xor'ed with the IV.
CryptoMethods.Decrypt(state, tempBuffer, blockSize,
tempBuffer, 0);
// XOR the IV with the temporary buffer to get plaintext.
for (index = blockSize - 1; index >= 0; --index)
{
outputBuffer[offset + index] =
(byte)(iv[index] ^ tempBuffer[index]);
}
// Copy the original ciphertext to the IV.
Array.Copy(tempBuffer, blockSize, iv, 0, blockSize);
// Advance to the next block and clear the temporary block.
offset += blockSize;
transform.tempSize = 0;
for (index = 2 * blockSize - 1; index >= blockSize; --index)
{
tempBuffer[index] = (byte)0x00;
}
}
// Process all of the blocks in the input, minus one.
while (inputCount > blockSize)
{
// Decrypt the ciphertext to get the plaintext
// xor'ed with the IV.
CryptoMethods.Decrypt(state, inputBuffer, inputOffset,
tempBuffer, 0);
// XOR the IV with the temporary buffer to get plaintext.
for (index = blockSize - 1; index >= 0; --index)
{
outputBuffer[offset + index] =
(byte)(iv[index] ^ tempBuffer[index]);
}
// Copy the original ciphertext to the IV.
Array.Copy(inputBuffer, inputOffset, iv, 0, blockSize);
// Advance to the next block.
inputOffset += blockSize;
inputCount -= blockSize;
offset += blockSize;
}
// Save the last block for next time.
if (inputCount > 0)
{
Array.Copy(inputBuffer, inputOffset,
tempBuffer, blockSize, inputCount);
transform.tempSize = inputCount;
}
// Clear the temporary buffer to protect sensitive data.
for (index = blockSize - 1; index >= 0; --index)
{
tempBuffer[index] = (byte)0x00;
}
// Finished.
return(offset - outputOffset);
}