Question

I’m playing around with text transformations – ciphers. From all that I have surveyed it seems that all of these algorithms either break even in terms of transformed message length, or get larger. Are there any known algorithms/text transformations that when applied to a message actually make the message smaller (not counting the key, of course)?

For instance, RSA, when you encode the message, makes the encrypted message quite a bit larger than the original. Is there any such thing as that only the message becomes smaller, instead of larger, after (encryption, transformation, etc whatever you want to call it)?

I’m not doing this as part of security, so whether or not it’s hackable is not of any interest to me.

P.S. I’ve done a lot of research in this area already through search engines (google, wikipedia, etc) but I have found no results. I don’t want to say that such a technique doesn’t exist without at least posting the question publicly first.

Thanks!

Answer 1

Compression tries to make input smaller. Obviously lossless compression will not make every input smaller, since that’s impossible.

You can encrypt the compressed input if you want that. In principle compression and encryption are orthogonal concepts, but in some situations the length of the compressed text can be used to attack the system.