# Questions tagged [des]

(or Data Encryption Standard), a (symmetric) block cipher using a 64 bit block size, with keys of size 56 bit, the standard US block cipher from 1976 to 2001.

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### permutation,how that more than 60% of possible mappings will have at least one fixed point [closed]

Let $\pi(.)$ be a permutation over the integers $\{0,1,2,…,(2^𝑛 − 1)\}$. Fixing the key, DES is such a permutation for $n=64$. We say $\pi$ has a fixed point if $\pi(𝑚) = 𝑚$ for some $m$. As you ...
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### Prove how to brute-force the double encryption with complexity 2^57 rather than 2^112?

We know that DES has key length that is too short to defend brute-force attack. One idea to improve DES was to encrypt a message using DES twice with two different keys. Let E be the encryption ...
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### If the first key-bit is flipped, which DES s-boxes are affected?

Instead of the input bit being flipped... if the 1st bit of the key is being flipped, which s-boxes are affected during encryption/decryption of DES?
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### DES F function never injective?

Now i know that the F function doesn't have to be injective, but is it NEVER injective? or is it possible to have an injective F function?
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### How was the special DES key 0E329232EA6D0D73 found?

The DES key 0E329232EA6D0D73 has the unusual property that decrypting a ciphertext block consisting entirely of zeros gives a plaintext block consisting of eight repetitions of the same byte (0x87). ...
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### How to determine the maximum number of times the DES algorithm needs to be run?

I am only a beginner in cryptography and I am getting confused by the following: Question Consider a known-plaintext attack performed on a double-DES cryptosystem. (a) Determine the maximum number ...
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### Design flaws in the round-key generation mechanism of Data Encryption Standard (DES) [duplicate]

I am beginner in Cryptography, I want to ask that what are two design flaws in the round-key generation mechanism of Data Encryption Standard (DES) that can lead to the occurrence of weak and semi-...
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### Proof of probability of weak keys in block cipher

My textbook has the following theorem: Given a block cipher with a key length of K bits and blocksize of n bits as well as t plaintext-ciphertext pairs, the expected number of false keys which ...
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### DES-CBC with random IV - how big is the keyspace? Can COTS tools crack it?

I've spent the night reversing the implementation of the 'Basic Text Encryptor' from Jasypt . The algorithm is defined in documentation as 'PBEWithMD5AndDES'. The implementation is this: A ...
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### DES Meet in the Middle

My professor showed us the basics of DES, and then displayed this slide where the Meet in the Middle attack can be used as a way of cracking DES. I believe at this stage we are doing 2DES, as opposed ...
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### DES complement trick [duplicate]

My professor showed us the basics of DES, and then displayed this slide where the Complement Trick can be used as a way of cracking DES. Could someone explain the math to me please?
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### Why isn't data encrypted with mutiple ciphers?

Why isn't data encrypted with multiple uncompromised (so far) ciphers? Feel free to answer for a single private key for both and separate private keys. For example, encrypting data with TwoFish and ...
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### How do additional input output pairs help with a Meet in the Middle attack on Double DES

Double DES is vulnerable to a Meet in the Middle attack where an attacker generates intermediate values and then matches them up to find candidate key pairs. For Double DES using $56$ bit keys and $1$ ...