4 ms·
Surely you don't mean random. At best you mean pseudo-random, but either way, the result isn't random (because after all, you'd be left with something scrambled
by quinndupont 10y ago
Surely you don't mean random. At best you mean pseudo-random, but either way, the result isn't random (because after all, you'd be left with something scrambled, not encrypted). That's the entire conceptual point of cryptography.
- Ar-Curunir 10y agoNo, I do mean random. Block ciphers, such as AES, model PRFs. One cannot get IND-CPA security by just passing the message into AES ala ECB mode. Instead, one has to use randomness, in the form of a nonce, as in CBC mode, to obtain IND-CPA security. Sure, the resulting ciphertext is only computationally indistinguishable from random. But the point of IND-CPA security is that one can't differentiate between two encryptions of different messages. Adding randomness gives you this.
- quinndupont 10y agoAah, but that's the rub. The result isn't actually random, it is only "computationally indistinguishable" (or, some lower threshold, since it is only in the last few decades of the multi-millennia history of crypto that this has been true). I'm not denying that pseudo-randomness (or even in very limited cases, real randomness) is used in most varients of crypto today, rather, I am suggesting that despite this, the end result is precisely the opposite: a message so highly ordered that it is "computationally indistinguishable", merely masquerading as random.