> Encrypted data is bits and bytes like everything else. You can compress it. (Maybe not as well as unencrypted text, but still.) Due to the pigeonhole princip

> Encrypted data is bits and bytes like everything else. You can compress it. (Maybe not as well as unencrypted text, but still.) Due to the pigeonhole principle, to be able to make some inputs shorter you have to make some inputs longer. The way compression works is by making more likely inputs shorter, while making unlikely inputs longer. But for encrypted data, if your encryption method is good (that is, not ECB mode), all possible values are equally likely (unless you known the secret key).