cryptography - Are there Ciphers that get smaller?

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

压缩试图使输入更小。显然无损压缩不会使每个输入更小，因为那是不可能的。

如果需要，您可以加密压缩的输入。原则上压缩和加密是正交的概念，但在某些情况下，压缩文本的长度可以用来攻击系统。

Answer 2

起初我想到了语言转换。一些英文短语翻译成一个中文符号。这不是一个严格的数学例子，但我想它是合格的。

或者，从位角度来看，不可能在 1 位中加密/编码 2 位信息。