Since you say true security is not needed, just casual security, and you want to shorten strings, perhaps you might be better off compressing your string. A compressed string obviously will not be human readable, so it is effectively "encrypted" for most intents and purposes. Algorithm::Huffman , and Archive::Zip
would be good places to start.
I would limit that to "it will take a little work to decompress the string" or "some people won't be able to decompress the string". It would only take a very slightly sophisticated attacker to bypass that, and it's primarily a security-by-obscurity approach. It may be better than nothing, but it certainly shouldn't be regarded as the same level of security as using a modern encryption algorithm.