Score:0

Use same key k in deterministic counter mode to encrypt two different plaintext

sn flag

What goes wrong if we use the same key k in deterministic counter mode to encrypt two different plaintext messages m0 /= m1.

It is not true that c0 = c1, because we XOR output of m0 with input of m1 in counter mode. As a result, c0 cannot equal c1, and c1 cannot be said to be the same as c0.

Could this be true?

Attacker find two c0 and c1, then find m0 and m1.

Currently, attackers can check all new messages they send or receive. He found the key using ciphertext and plaintext.

poncho avatar
my flag
Is this homework? If you're asking because you're thinking of doing this in practice, well, **don't do that**
Amirhossein avatar
sn flag
Yes, but I'l final exam start about 9hours ago. I need last true answer.
forest avatar
vn flag
Are you using a different nonce?
Amirhossein avatar
sn flag
@forest yes, using diffrent nonce.
Amirhossein avatar
sn flag
@forest yes, using diffrent nonce.
Score:3
my flag

This is a homework question; by policy, we don't give the final answer to homework questions - you learn better if you figure the answer out yourself.

That said, we will give hints - here are a couple:

  • If we have $C_0 = P_0 \oplus AESCTR_{key}$ and $C_1 = P_1 \oplus AESCRT_{key}$, how are $C_0$ and $C_1$ related?

  • If we can deduce $P_0 \oplus P_1$, can we use that to recover $P_0, P_1$? Actually, that depends on the distribution that $P_0, P_1$ are drawn from - for some common distributions (e.g. ASCII English) we can.

I sit in a Tesla and translated this thread with Ai:

mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.