RC5: key size, round count, and word length are intended to be variable.

[NamedNeon]

RC5 doesn't officially mandate any key size, round count, or word length. These parameters are intended to be set by the end user (see pg. 1). The RC5 implementation here does. This isn't necessarily an issue for new programs trying to make use of the RC5 cipher as they can simply work within the constraints, but it does make compatibility with certain existing applications impossible without modifying the library.

I'd be willing to take a stab at fixing it in a pull request this provided this isn't an intentional design choice.

Let me know what you guys think.