Implements the free unpatented CAST block cipher. See RFC 2144 for details. The SSLeay implementation of CAST currently only supports keysizes of 11-16 bytes. The package will raise an error if you use keys of size 5-10 bytes. Eric Young will fix this in an upcoming release of SSLeay.
All cipher objects provide a similar interface.
Block ciphers will generally expect the string to have a multiple of their blocksize as length while stream ciphers can handle arbitrary length strings. The internal state of the cipher object is updated according to the mode set at creation time. This is the inverse of the encrypt method. The chances of picking a weak key are very low, so you might as well not check for them. Mode the cipher operates in.