StreamTransformationFilter
| Documentation |
| #include <cryptopp/filters.h> |
A StreamTransformationFilter allows a symmetric cipher to participate in pipelining. The filter also handles details such as padding.
Constructor
StreamTransformationFilter (StreamTransformation &c,
BufferedTransformation *attachment=NULL,
BlockPaddingScheme padding=DEFAULT_PADDING,
bool allowAuthenticatedSymmetricCipher=false)
c is a cipher that inherits from StreamTransformation. Descendents can be found at StreamTransformation Class Reference. For block ciphers, its going to be a mode object like CBC_Mode<T>::Encryption or OFB_Mode<T>::Decryption by way of CipherModeBase. For stream ciphers, its going to be a stream cipher like Salsa20::Encryption or Panama::Decryption.
attachment is a BufferedTransformation, such as another filter or sink. If attachment is NULL, then the StreamTransformationFilter object will internally accumulate the output byte stream.
padding is a padding scheme enumeration. The values of BlockPaddingScheme are NO_PADDING, ZEROS_PADDING, PKCS_PADDING, ONE_AND_ZEROS_PADDING and DEFAULT_PADDING. DEFAULT_PADDING is PKCS_PADDING for block ciphers.
allowAuthenticatedSymmetricCipher should always be false. If you need an authenticated encryption filter, then you should use AuthenticatedEncryptionFilter and AuthenticatedDecryptionFilter.
Sample
In the example below, CBC_Mode< AES >::Encryption is the StreamTransformation object.
SecByteBlock key[ AES::DEFAULT_KEYLENGTH ];
SecByteBlock iv[ AES::BLOCKSIZE ];
...
// Encryptor
CBC_Mode< AES >::Encryption enc( key, key.size(), iv, iv.size() );
// Encryption
CryptoPP::StringSource ss( plainText, true,
new CryptoPP::StreamTransformationFilter( enc,
new CryptoPP::StringSink( cipherText )
) // StreamTransformationFilter
); // StringSource
To specify a padding scheme, use the overloaded constructor.
...
// Encryption
CryptoPP::StringSource ss( plainText, true,
new CryptoPP::StreamTransformationFilter( enc,
new CryptoPP::StringSink( cipherText ),
BlockPaddingScheme::NO_PADDING
) // StreamTransformationFilter
); // StringSource
