# 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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### What are the concrete changes the NSA did to the algorithm before DES was published?

It's common knowledge that the NSA, before publication of DES, tweaked the algorithm to improve its resistance against differential cryptanalysis. Schneier writes some of this on his blog, for example ...
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### Increasing the parallelization of Triple-DES

Triple-DES encrypts with the first key, then the second key, then the third key. Two keys are sitting around waiting. Why not encrypt with all three keys at the same time? You take 192 bits of ...
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### Variant of DES and breaking the 16 round DES

Consider a variant of DES algorithm, called DES-WEAK. In DES-WEAK, there is no permutation P in a round and all the S-boxes are replaced. The new S-boxes are all identical and defined as follows. Let ...
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1 vote
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### How does one produce this in the linear cryptanalysis of DES

I understand how this linear approximation board below is produced, but I can't understand how this second board is produced using the first one and finally how the pilling-up lemma values are ...
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### DES SBOX Output with Bitslice

I am not understanding how to compute the output bits of a 6-to-4-SBOX with bitslice technique in DES. Matthew Kwan made a brief recap in his paper "Reducing the Gate Count of Bitslice DES" ...
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### Matsui's linear attack on 5-round DES

I'm trying to understand Mitsuru Matsui's "Linear Cryptanalysis Method for DES Cipher", specifically the attack he describes at the end of section 5, on 5-round DES. I followed the attack on ...
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### Is there any real attack deployed on the CTR mode over history?

The CTR mode, with its CPA security, is one of the malleable block cipher mode of operations. An attacker can simply modify the bits of the ciphertext stream in their advance. This is due to the lack ...
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1 vote
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### Disrupting MITM attack against 3DES by intermingling plaintext and inter-mediate ciphertext between rounds

Let's say someone implements 3DES with three separate 56-bit keys and an attacker is attempting to execute a MITM attack. Here is the encryption plan designed to attempt to disrupt the MITM attack, or ...
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### Proof that no DES key makes encryption identity

How can we prove that no DES key makes encryption the identity function? That is: $\;\forall K\in\{0,1\}^{56}\quad\exists M\in\{0,1\}^{64}\quad E_K(M)\ne M$ Note: anyone disproving this proposition ...
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### DES : Is Double Encryption using same key twice equivalent to single DES using different key but of same size

If we encrypt a plain text using Double DES but with same key K1, Can we get the same result as if we would encrypt the plain text using single DES but with different key, say K2. What I'm asking is ...
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### How to find Key with DES, ECB hash and plaintext [closed]

I have two ciphertexts. Encryption algorithm: DES in ECB mode. Ciphertext: 72EE3532F904CE2AAA966C723C463F294CA8AB1C11E9E0B304BBB6A8E2BD1F34 Plaintext: DetectedSpambotsRemailedMalwares Ciphertext: ...
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### How to calculate size of a codebook lookup table to break block cipher?

I was reading a book called Serious Cryptography. There is a page saying that block size must be large enough to prevent codebook attacks: When 16-bit blocks are used, the lookup table needs only 2^...
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