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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DES and AES cryptography

I have a question that I can't answer: A plain text has been encrypted 3 times in a DES method with 3 different keys 56 bit each, after it the text was encrypted for the forth time using a AES ...
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aside from DES has the NSA ever strengthened algorithms?

When DES was originally developed, the NSA changed the s-boxes. For decades people thought that their changes introduced a backdoor but then it was discovered that their changes actually strengthened ...
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161 views

How many reversible gates would DES require?

How many reversible gates (said counting Toffoli and Controlled NOT, with free NOT) would be required to reversibly implement $(K,P)\mapsto(G,C)$ for the block cipher DES? $P$ is the plaintext, $C$ ...
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Bitslice DES decryption

I would like to implement fast DES decryption using Bitslice technique. Without bitslice DES technique, I have already done decrpytion in this source code by changing the for loop from 15 to 0. In ...
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82 views

Effect of longer key on DES security

I am reading a book on cryptography and the author states that one of the complaints of the research community was that DES key length was chosen to be too short. I am trying to depict how DES would ...
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1answer
231 views

DES - Weakness in Sbox

In the book "Introduction to Cryptography with Coding Theory ", in the chapter about the Differential Cryptanalysis for Four Rounds for DES algorithm, the authors say: There is a weakness in the ...
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Is uneven DES keybit use exploitable?

Question: Is there any cryptanalytic leverage to be had from the fact that some of the 56 "raw" keybits of DES are used more & less often than others? Observation: over the course of the 16 ...
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0answers
41 views

what if the S-boxes in DES were “optimal”

if we assume that the s-boxes in DES were optimal. that is for each s-box, every cell in the DDT equals to 4. is there a differential characteristic in a good probability?
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51 views

differential cryptanalysis on the second round of 4-variant DES

I am using differential cryptanalysis to attack the second key of a 4-variant DES and I am using Shamir and biham book as a reference . they say that we should choose two input Xor P3 and P4 that ...
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0answers
68 views

Can someone help me understand how to get the I/O relation equations in DES S- boxes

I am referring to the equations that have been discussed in Nicolas T. Courtois and Gregory V. Bard's Algebraic Cryptanalysis of the Data Encryption Standard (in proceedings of Cryptography and Coding ...
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0answers
418 views

Number of pairs needed to attack Double DES?

I'm having trouble understanding why,in order to do a brute force attack on a double DES (2 keys), one needs to have at least 2 pairs of known plain text? Same with 3DES (3 keys) one needs to have 3 ...
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144 views

Does the encryption algorithm DES perform random permutations? If so how is information not lost?

Before round 1 begins, all 64 bits of an incoming message and all 56 bits of the secret key are separately permuted (shuffled) My question is this : Is the shuffling of the bits performed randomly? ...
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94 views

prepaid meters that rely on a disconnected system

i have some experience with cryptography in the banking sectors, mostly in block ciphers like DES 3DES etc. im interested in prepaid electricity meters as it is a number that is generated from a ...
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791 views

About the Algebraic Normal Form (ANF) of S-Box in DES

I've thought up a way to represent the transformation of S-Box in DES by ANF. Let $x_i\;(1\le i\le 6)$ be the input of an S-Box, $y_i\;(1\le i\le 4)$ be the output, for example, then $$y_1= 1\oplus ...
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58 views

Delinearization in whitebox techniques

I'm reading through Chow et al.'s paper and Link et al.'s paper. There's a part I don't understand about Delinearization. They convert some steps of AES/DES into a Matrix, then divide the matrix in ...
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35 views

DES P box design criteria

I hope somebody can help me to find out how DES P box has designed. I am doing DES by hand so I want to know how these numbers are arranged?
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73 views

How is pipelined DES different from sequential DES?

I implemented DES Coder in VHDL using ISE IDE by Xilinx in sequential architecture which was pretty easy and straightforward. Now my task is to do the same using pipelined architecture so that the ...
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174 views

Triple DES: Does knowing the plaintext limit my keyspace for brute force?

My goal is to try and decrypt a single 8 byte block of a Triple DES encrypted data block and in doing so discovering the 8 byte keys that were used. This is mostly an academic exercise but could ...
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62 views

What are the positive consequences for choosing 8 S-boxes for DES vs 1 S-box for AES?

What are the positive consequences for choosing 8 S-boxes for DES vs 1 S-box for AES? I could guess side channel resistance, but I can't find anything on it.
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237 views

Is 3 rounds more secure than 2 in this simplified DES?

Consider the following simplification of DES: a plaintext message block of $2n$ bits of length is divided into two blocks of length $n$ (left half $L_0$ and right half $L_1$). In other words, the ...
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627 views

CBC MAC and DES combined question?

Suppose that we want to develop a MAC scheme which is as secure as Triple-DES CBC-MAC and at the same time as efficient as Single-DES CBC-MAC. We come up with the following idea: Except the last ...
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617 views

Method and explanation for calculating difference in speed between DES and RSA

Our assignment asks us to convert an RSA speed in bytes per second to a DES speed in bytes per second. Our professor's treatment of this ("RSA is 100 times slower than DES") seems insufficient. Could ...
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1answer
62 views

How to figure out DES mode used given plaintext and ciphertext?

In DES, I'm given the following exercise. - How can I find out which part of the plaintext each ciphertext message corresponds to, and which mode they were each encrypted with?
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1answer
58 views

Would Triple DES-X with 7 keys be much slower than standard Triple DES?

Since a single hardware pass of an XOR with a 64 bit key is very fast, would Triple DES-X using seven 64 bit keys used in the following manner be virtually identical in terms of code size, memory ...
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40 views

In DES what happens if the 32-bit swap at the end is not performed while decrypting?

I know that the swap at the end of DES is so that the same algorithm can be used for encryption and decryption, but I'm wondering what happens if one does not include the swap at the end. What is the ...
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Differential cryptanalysis for DES reduced to Four Rounds and about S/N

I'm reading the paper "Differential Cryptanalysis of the Data Encryption Standard(2009)" and I was stuck in a certain part while reading it. In chapter 4, they explained about differential ...
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35 views

Lineary of Sbox in DES

I'm not a mathematician, and i would like to understand in the most concise way (if possible) why choosing linear S-Box functions makes the DES algorithm attackable. Thanks
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In DES : Matsui's notation(LC) vs Biham's notation(DC)

I'm doing linear attack for 8 rounds DES. And I just wondering about the difference between matsui's notation and Biham's notation. In Matsui's paper, numbers bits from 0 to 63 from right to left. In ...
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55 views

Meet-in-the-middle attack (different block cipher modes)

Does a meet-in-the-middle attack on depend on the used modes for block ciphers? encryption: $C_i$ = $D_{K2}$($D_{K1}$($E_{K1}$($P_i$ $\oplus$ $C''_{i-1}$))) $\oplus$ $C'_{i-1}$ and $IV_1$ = $C''_0$ = ...
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good OmegaP for characteristic to use in differential cryptanalysis on DES

how to choose a good OmegaP(input difference) for the characteristic used in differential crypt-analysis on DES?
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Is it possible for an attacker to determine the original input to the S-Boxes in DES?

I am learning about DES, a Feistel 64-bit block cipher with 16 rounds. Is it possible that an intruder can determine the original input to the S-Boxes?
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179 views

If a DES key correctly decrypts one message, what's the probability it's the real key?

Suppose an adversary gets a message-ciphertext pair $(M,C)$, where $C=DES_K(M)$. They do an exhaustive key reach to locate the lexicographically first key $T$ for which $C=DES_T(M)$. What's the ...
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901 views

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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1answer
631 views

Problem with implementing DES in python

i'm implementing DES in python and i've stumbled upon a problem i can't really find the problem, after debugging it i narrowed it down to this function, can anyone tell me if i'm implementing the DES ...