public async Task <byte[]> BeginAsync()
{
if (_ubiqWebServices == null)
{
throw new ObjectDisposedException(GetType().Name);
}
else if (_aesGcmBlockCipher != null)
{
throw new InvalidOperationException("encryption in progress");
}
if (_encryptionKey == null)
{
// JIT: request encryption key from server
_encryptionKey = await _ubiqWebServices.GetEncryptionKeyAsync(_usesRequested).ConfigureAwait(false);
}
// check key 'usage count' against server-specified limit
if (_useCount > _encryptionKey.MaxUses)
{
throw new InvalidOperationException("maximum key uses exceeded");
}
_useCount++;
var algorithmInfo = new AlgorithmInfo(_encryptionKey.SecurityModel.Algorithm);
// generate random IV for encryption
byte[] initVector = new byte[algorithmInfo.InitVectorLength];
var random = RandomNumberGenerator.Create();
random.GetBytes(initVector);
var cipherHeader = new CipherHeader
{
Version = 0,
Flags = CipherHeader.FLAGS_AAD_ENABLED,
AlgorithmId = algorithmInfo.Id,
InitVectorLength = (byte)initVector.Length,
EncryptedDataKeyLength = (short)_encryptionKey.EncryptedDataKeyBytes.Length,
InitVectorBytes = initVector,
EncryptedDataKeyBytes = _encryptionKey.EncryptedDataKeyBytes
};
// note: include cipher header bytes in AES result!
var cipherHeaderBytes = cipherHeader.Serialize();
_aesGcmBlockCipher = new AesGcmBlockCipher(
forEncryption: true,
algorithmInfo: algorithmInfo,
key: _encryptionKey.UnwrappedDataKey,
initVector: initVector,
additionalBytes: cipherHeaderBytes);
return(cipherHeaderBytes);
}
public byte[] Begin()
{
if (_ubiqWebServices == null)
{
throw new ObjectDisposedException(GetType().Name);
}
else if (_aesGcmBlockCipher != null)
{
throw new InvalidOperationException("decryption in progress");
}
// prepare to receive initial header bytes
_cipherHeader = null;
_byteBuffer = null;
// note: cached '_decryptionKey' may be present from a previous decryption run
return(new byte[0]);
}
// each encryption has a header on it that identifies the algorithm
// used and an encryption of the data key that was used to encrypt
// the original plain text. there is no guarantee how much of that
// data will be passed to this function or how many times this
// function will be called to process all of the data. to that end,
// this function buffers data internally, when it is unable to
// process it.
// the function buffers data internally until the entire header is
// received. once the header has been received, the encrypted data
// key is sent to the server for decryption. after the header has
// been successfully handled, this function always decrypts all of
// the data in its internal buffer
public async Task <byte[]> UpdateAsync(byte[] cipherBytes, int offset, int count)
{
if (_ubiqWebServices == null)
{
throw new ObjectDisposedException(GetType().Name);
}
byte[] plainBytes = new byte[0]; // returned
if (_byteBuffer == null)
{
_byteBuffer = new ByteBuffer();
}
// make sure new data is appended to end
_byteBuffer.Enqueue(cipherBytes, offset, count);
if (_cipherHeader == null)
{
// see if we've got enough data for the header record
using (var byteStream = new MemoryStream(_byteBuffer.Peek()))
{
_cipherHeader = CipherHeader.Deserialize(byteStream);
}
if (_cipherHeader != null)
{
// success: prune cipher header bytes from the buffer
_byteBuffer.Dequeue(_cipherHeader.Length());
if (_decryptionKey != null)
{
// See if we can reuse the key from a previous decryption, meaning
// the new data was encrypted with the same key as the old data - i.e.
// both cipher headers have the same key.
//
// If not, clear the previous decryption key.
if (!_cipherHeader.EncryptedDataKeyBytes.SequenceEqual(
_decryptionKey.LastCipherHeaderEncryptedDataKeyBytes))
{
await ResetAsync().ConfigureAwait(false);
}
}
// If needed, use the header info to fetch the decryption key.
if (_decryptionKey == null)
{
// JIT: request encryption key from server
_decryptionKey = await _ubiqWebServices.GetDecryptionKeyAsync(_cipherHeader.EncryptedDataKeyBytes).ConfigureAwait(false);
}
if (_decryptionKey != null)
{
var algorithmInfo = new AlgorithmInfo(_cipherHeader.AlgorithmId);
// save key extracted from header to detect future key changes
_decryptionKey.LastCipherHeaderEncryptedDataKeyBytes = _cipherHeader.EncryptedDataKeyBytes;
// create decryptor from header-specified algorithm + server-supplied decryption key
_aesGcmBlockCipher = new AesGcmBlockCipher(forEncryption: false,
algorithmInfo: algorithmInfo,
key: _decryptionKey.UnwrappedDataKey,
initVector: _cipherHeader.InitVectorBytes,
additionalBytes: ((_cipherHeader.Flags & CipherHeader.FLAGS_AAD_ENABLED) != 0)
? _cipherHeader.Serialize()
: null);
_decryptionKey.KeyUseCount++;
}
}
else
{
// holding pattern... need more header bytes
return(plainBytes);
}
}
if ((_decryptionKey != null) && (_aesGcmBlockCipher != null))
{
// pass all available buffered bytes to the decryptor
if (_byteBuffer.Length > 0)
{
// tricky: the block cipher object will process all provided ciphertext
// (including the trailing MAC signature), but may only return a subset of that
// as plaintext
var bufferedBytes = _byteBuffer.Dequeue(_byteBuffer.Length);
plainBytes = _aesGcmBlockCipher.Update(bufferedBytes, 0, bufferedBytes.Length);
}
}
return(plainBytes);
}
