Comment on Order
harbor9964@lemmy.world 10 months agoCompressing what themselves? Compress then encrypt leaks information about the data being encrypted if an adversary can affect some part of the data being encrypted. If the data is at rest and repeated encryptions are needed , then this isn’t a concern.
bastian_5@sh.itjust.works 10 months ago
Compress the encrypted data. You’re talking about encrypting compressed data, this was talking about compressing encrypted data.
bioemerl@kbin.social 10 months ago
Technically you would be fine to compress the encrypted data, but encrypted data doesn't compress well so it's not really worth your time
bastian_5@sh.itjust.works 10 months ago
Depends on if you’re using lossless or lossy compression. Lossless compression will usually make it bigger, because it relies entirely on data being formatted so their are common patterns or elements that can be described with fewer parts. Like, an ok compression algorithm for a book written in English and stored as Unicode would be to convert it to ASCII and have a thing that will denote Unicode if there happens to be anything that can’t convert. An encrypted version of that book would look indestinguishable from random characters, so compressing it at that point would just put that Unicode denoter before every single character, making the book end up taking more space.
bioemerl@kbin.social 10 months ago
The problem is that when you compress before you encrypt, the file size becomes a source of data about the contents. If an attacker has control of part of the data - say - a query string, they can use that to repeatedly add things to your data and see how the size changes as a result.