Modes ECB and CBC can only handle full 16-byte frames. This means the length of every strict bytestring passed in must be a multiple of 16; when using lazy bytestrings, its component strict bytestrings must all satisfy this.

Other modes can handle bytestrings of any length. However, encrypting a bytestring of length 5 and then one of length 4 is not the same operation as encrypting a single bytestring of length 9; they are internally padded to a multiple of 16 bytes.

For OFB and CTR, Encrypt and Decrypt are the same operation. For CTR, the IV is the initial value of the counter.

A class of things that can be crypted

The crypt function returns incremental results as well as appending them to the result bytestring.