Evaluation of prediction of probability is a DES structure

Sudhir Kumar Sahoo

6/12/23, 11:29 AM

Suppose you are given $DES_k(m)$ for some unknown $k$ and $m$, where DES() is the usual DES scheme. With what probability can you predict, for example, the 12-th bit in the output of $DES_{\bar{k}}(\bar{m})$. Here $\bar{m} (resp. \bar{k})$ denotes the bitwise complement of m (resp. k).

In this question, as we know that we are using Feistel cipher with $n=32$ $r = 16$ but how to evaluate the prediction of probability as for each block we know the probability of prediction is $\frac{1}{2^n}$ where $n$ is a number of plain text bits and here 12 bit output which is ciphertext so is the answer going to be $\frac{1}{2^{12}}$. Please correctify me if I am wrong

0 + 0

des

aes

kelalaka

6/12/23, 12:06 PM

Is this a HW question? Please indicate this.

DannyNiu

6/12/23, 1:18 PM

kelalaka is right, we care about academic integrity, so for homework questions we only provide hints. I've seen your attempt at solving the task, so I up-voted you. [Page](https://crypto.stackexchange.com/help/on-topic) from the help center.

DannyNiu

6/12/23, 1:18 PM

@kelalaka Some may confuse HW as hardware :p

kodlu

6/12/23, 2:03 PM

prediction of probability is not a meaningful phrase. define it propertly

Elon Musk

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

EN: Evaluation of prediction of probability is a DES structure

TH: การประเมินการทำนายความน่าจะเป็นเป็นโครงสร้าง DES

RO: Evaluarea predicției probabilității este o structură DES

RU: Оценка предсказания вероятности представляет собой структуру DES.

VI: Đánh giá dự đoán xác suất là một cấu trúc DES

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