> It wont be a huge difference in file size, but it will be smaller.
may be smaller, not all outputs will be smaller, this is true of all lossless compression algorithms:
may be smaller, not all outputs will be smaller, this is true of all lossless compression algorithms:
The real question is, can you reliably compress encrypted messages in general? And, given that the encryption is not broken, the answer is no.
In theory, some random outputs will be compressible by common tools (for example, a file that's all zeroes). However, the probability of encountering a random file that compresses more than the overhead from any common compression tool is vanishingly small.
No they're not. They're saying that as a class, you cannot compress the data. That is a statement about what happens in aggregate. And the aggregate result of trying to compress securely-encrypted data is that you don't save bytes. Even just having the option of compression does not save bytes, because you have to store the choice.