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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I'm studying about differential cryptanalysis in DES. I need to make the DDT through python [duplicate]

I just made DES algorithm(encryption, decryption) using python. And I want to attack 1,2 4,8 .. round DES. For that, I need to make the DDT code. Could you guys help me to make the DDT? Thank you.
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Block cipher information leakage using same key

This is from a previous exam question and I'm not really sure how to approach this properly We're using a block-cipher mode that encrypts $C_i$ = $E_k$ ($P_i$ $\oplus$ $C_{i-1}$ $\oplus$ $P_{...
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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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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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Why is DES secure against differential cryptanalysis

I was wondering, why DES is secure against Differential Attacks. Some of the S-Boxes have a very bad Differential Uniformity, only one has a DU of 4, 3 have a DU of 6 and the others are much worse. ...
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Meet-in-the-middle attack (on custom encryption scheme) [duplicate]

This is a question I had from an exercise session. Exercise: First we do DES in CBC encryption mode using a key $K_1$ and $IV_1 = O^n$. Then we do DES in ECB decryption mode using $K_1$. And then DES ...
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Symmetric encryption construction (meet-in-the-middle attack)

This is a question I had from an exercise session. First we do DES in CBC encryption mode using a key $K_1$ and $IV_1 = O^n$. Then we do DES in ECB decryption mode using $K_1$. And then DES in CBC ...
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DES parity bits

The key is nominally stored or transmitted as 8 bytes, each with odd parity. According to ANSI X3.92-1981 (Now, known as ANSI INCITS 92-1981), section 3.5: One bit in each 8-bit byte of ...
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Can $AES_{k1}(m)$ be equal to $AES_{k2}(m)$? [duplicate]

Context: We have a generic bloc cipher composed of an encryption function $E_k$ and a decryption function $D_k$ operating on blocs of $n$ bits. For a key $k$ fixed, we can see $E_k$ as a pseudo-...
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What are the separate single DES keys from a triple DES key?

Suppose my 192 bit triple DES key (in hex) is 0123456789ABCDEFFEDCBA987654321089ABCDEF01234567 What are the keys for the separate single DES operations? In this ...
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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 there any encryption algorithm that, with small change in input will produce big change in the encrypted output?

As stated in the title, I'm looking for an encryption algorithm with the characteristics that, when inputs are slightly different, the encrypted output will be VERY much different, to the point that ...
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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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Security of a block cipher if double encryption $E_{K_2} \circ E_{K_1}$ is always single encryption $E_{f(K_1,K_2)}$

If there always existed a $k_3$ such that $\operatorname{DES}(k_2, \operatorname{DES}(k_1, M)) = \operatorname{DES}(k_3, M)$, how would that affect the security of $\operatorname{DES}$?
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Getting the s-box input from its output in differential cryptanalysis on DES

If we try to get K4 using differential cryptanalysis on 4-variant DES, how can we get the input of a certain S-box if we know it's output? This seems hard to do since the substitution operation is ...
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Determine the original input to the S-Boxes

The 8 S-boxes of DES were designed to provide resistance against attacks. Small modifications to an S-box can significantly weaken DES. Can the original input (the result of XOR on the expansion ...
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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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triple-des simple questtion [duplicate]

Why do we use encrypt-decrypt-encrypt (EDE) in 3DES, rather than encrypting three times? in this link, we use EDE Mode usually. when we use one key, in this case, Encryption -> Decryption result ...
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Would DES be secure with 128 bit keys?

Assuming you only modify the key schedule so that each of a 128-bit key is used at least once, would DES be about as secure as other ciphers such as AES? I am not talking about 2DES/3DES or other ...
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Can neural cryptanalysis be applied to AES?

In this Wikipedia article about Neural cryptography (section applications) it states: In 1995, Sebastien Dourlens applied neural networks to cryptanalyze DES by allowing the networks to learn how ...
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DES/AES invertibility

My professor has posted a couple of practice questions that so far I haven't been able to find the answer for and I was hoping you could help. DES would remain invertible—it would still be ...
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External data loading in DES

Trying to write a C program that implements the DES standard (FIPS 46-3). I am unsure about how the standard should be interpreted when computing the various permutations specified in the document, ...
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Parity checking on DES key if using ASCII chars

This is my first question here, so if I ask it to the wrong group or otherwise infringing the (written or unwritten) rules of the community, please bear with me. My problem is this: In an exercise in ...
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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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Would XDES be more secure than 3DES, where X is a number > 3?

Would XDES be more secure than 3DES, where X is a number > 3? Like 10DES... If so why aren't we using it?
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One-round feistel network (DES) attack

I can't find out how to break 1 round of feistel network (obtaining the key). I understand why this equation takes place: $R_1 \oplus L_0 = f(R_0, k_1)$ EDIT: The function f looks like this: But ...
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64 DES full example with all the stages

I'm trying to write a code to perform encryption and decryption of 64-bit DES but I'm having a problem in verifying that my code is working correctly. My graduation project is about DES crypt-analysis ...
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In the RSA DES challenges, how did the contestants know they had found the right key considering they weren't given any plaintext?

If the contestants were given both the plaintext and ciphertext, it's straightforward. Just bruteforce all 56-bit keys until you find one that maps the given plaintext to the given ciphertext. But ...
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Statistical (innefective) Fault Attacks on DES

I read this paper: Exploiting Ineffective Fault Inductions on Symmetric Cryptography. I was wondering if the same idea is applicable for DES. I know both algorithms are symmetric but the idea is not ...
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What is meant by encrypting/decrypting a known plaintext/ciphertext with every possible key in meet-in-the-middle?

I am working on the Meet-in-the-middle attack on 2DES and I have got some questions I am not sure about. I read several websites/articles about it so I have got an idea of what it is and how it works. ...
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Matsui's Linear Cryptanalysis Lemma 1

In Matsui's paper (Linear Cryptanalysis Method for DES cipher), lemma 1. $NS(a, b)$ is even if $a=1,32$,or $33$, then $NS(a,b)=32$ for all $b$ He said that the following lemma is now trivial from ...
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Comparing DES and DES-X variation: $Enc(m) = DES_{k_1}(m \oplus k_2)$

I came across this question: Test the security of the following variation of DES-X cryptosystem, which uses 2 keys $k_1$ and $k_2$: $$Enc(m) = DES_{k_1}(m \oplus k_2)$$ (Basically, it uses the 2nd ...
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Encrypt twice with DES using same key ? $\operatorname{DES}(\operatorname{DES}(x,k), k)$

Does encrypting with $\operatorname{DES}$ in the following way $$\operatorname{DES}(\operatorname{DES}(x,k), k)$$ make $\operatorname{DES}$ as strong as $\operatorname{2DES}$ with 2 keys? Because we ...
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DES - encrypt 3 times - DES(DES(DES, k), k'), k) - stronger than 2DES with 2 different keys?

What if were to use DES in the following way: For a given plaintext x and key k we will perform: ...
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S-Box and it's linearity

I am trying to figure out why it is necessary S-box's to be nonlinear. I have been searching for some materials but was not able to find out clear proof why it means that if we use S-box in DES, it ...
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AES and DES - reusing the same round keys

Both DES and AES use key expansion to generate the round keys (for Feistel network or for the AddRoundKey operation). Each round uses a different key. Why do we need that? Why we cannot use the same ...
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What is the key space of a 2-key Triple DES

I am assuming the 2-key triple DES is equivalent to double des. I know the key size is 2x56 = 112 bits. Is this the key size the same as the keyspace? e.g. would the keyspace be 112 bits (2^112)
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How to find fixed points for DES weak keys

Can someone explain me this please I am a bit confused? It's from a texbook I am reading (block cipher companion) it says that: each weak key has $2^{32}$ fixed points $m$ where $\operatorname{...
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How can I prove that a Feistel round is its own inverse for DES?

I'm having difficulty on proving the fact that each round of DES algorithm is its own inverse. Can someone put a concise explanation for it please? If a function, say $f$ ,is its own inverse than $f(...
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Double DES meet in the middle attack: probability that wrong key pair remains

My Question is based on poncho's answer in this post. If you're doing a meet-in-the-middle attack against 2DES with only on a plaintext-ciphertext pair $(P,C)$, I understand that the expected amount ...
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With DES, is ECB encryption mode equivalent to CBC with null IV for short data blocks?

I got to this by experimentation, but can someone maybe provide an explanation for this?
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Question about DES S-boxes from Encryption to Decryption [duplicate]

While working on a homework assignment, I came across an interesting dilemma that I want to delve more into. The question essentially said to flip the first bit in the key string and then see what S ...
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Is DES secure under CBC?

I know DES is outdated, but will is is secure in CBC mode? Can anyone help me understand why not?
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Initial Permutation of DES

I'm implementing DES, but I cannot understand example. Plaintext: 123456ABCD132536 After initial permutation: 14A7D67818CA18AD Plaintext is 64-bits hexadecimal, so each character is 4-bits. The ...
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DES- If LSB is removed, are the key B and C the same?

I believe that in DES every 8th bit is ignored of the key. That means B and C are same if the LSB is ignored. So, shouldn't encrypting a message by the key all Bs be able to be decrypted by key with ...
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When using DES, how large would the key space be if we only use letters as characters?

Would it be safe? Or is it susceptible to brute force attacks or something else?
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If $E_{k_1}(p_1) = c_1$, what is the probability that there exists key $k_2$ such that $E_{k_2}(p_1) = c_1$?

Let $k_1$ be a 56 bit DES key that performs $E_{k_1}(p_1) = c_1$. What is the probability that there exists another key $k_2$ such that $E_{k_2}(p_1) = c_1$?
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Matsui's paper on Linear Cryptanalysis of DES

I am trying to derive the best linear approximation for one round DES. I read the question and answer Regarding matsui's Paper on Linear Cryptanalysis of DES several times but still could ...
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understanding the block bits for DES

I'm trying to understand cryptographic protocols, and I've started with the DES algorithm. DES specs: it uses 64 bits for the plaintext, 56 bits for the key, with a result of the same 64 bits of ...