init method
Initialise the cipher for processing.
Implementation
@override
void init(bool forEncryption, CipherParameters params) {
if (params is! ParametersWithIV) {
throw ArgumentError('CBC requer ParametersWithIV.');
}
_forEncryption = forEncryption;
_iv = Uint8List.fromList(params.iv);
_cbcV = Uint8List.fromList(_iv);
_cipher.init(forEncryption, params.parameters);
}