Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

1
vote
1answer
38 views

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 ...
0
votes
0answers
46 views

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 ...
0
votes
0answers
45 views

Why we use S-boxes in DES and Can we not use it? [closed]

your instructor ask us if we do not S-Boxes In DES, Does this make any difference there?
0
votes
0answers
77 views

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?
0
votes
0answers
30 views

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 ...
0
votes
0answers
10 views

I need help understanding bit order in DES [migrated]

I'm using a variety of references to study this algorithm, among others Christof Paar's book and classes. Currently I'm working on a custom C implementation of the algorithm, and am trying to ...
3
votes
1answer
442 views

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 ...
12
votes
1answer
2k views

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 ...
2
votes
1answer
55 views

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 ...
1
vote
2answers
48 views

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, ...
1
vote
1answer
50 views

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 ...
3
votes
0answers
39 views

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 ...
2
votes
1answer
78 views

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?
2
votes
1answer
86 views

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 ...
2
votes
2answers
93 views

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 ...
5
votes
1answer
872 views

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 ...
2
votes
1answer
54 views

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 ...
1
vote
2answers
57 views

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. ...
3
votes
1answer
75 views

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 ...
1
vote
1answer
103 views

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 ...
0
votes
1answer
70 views

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 ...
1
vote
2answers
101 views

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: ...
0
votes
1answer
117 views

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 ...
8
votes
1answer
210 views

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 ...
3
votes
2answers
302 views

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)
7
votes
1answer
161 views

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{...
4
votes
2answers
220 views

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(...
3
votes
1answer
161 views

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 ...
1
vote
1answer
159 views

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?
-1
votes
1answer
94 views

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 ...
3
votes
1answer
602 views

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?
0
votes
1answer
356 views

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 ...
0
votes
1answer
30 views

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 ...
2
votes
2answers
55 views

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?
3
votes
2answers
180 views

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 $E_{k_2}(p_1) = c_1$?
1
vote
1answer
52 views

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 ...
3
votes
2answers
615 views

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 ...
-1
votes
1answer
49 views

what is the impact of smaller bit size sbox

There are multiple S-boxes type, as DES uses 4 bit S-box and AES uses 8 bit S-box. I want to know how this effect the security?? If we use 4 bit or 8 bit. apart from the DC attack. Both provides ...
3
votes
1answer
246 views

Why does DES use a block size of 64 bit?

Why do we use 64 bit as block size for the DES algorithm? Is there a reason not to use another block size, for instance 72 bits?
3
votes
1answer
89 views

How are the PC-1 & PC-2 calculated for the DES block cipher?

How are the permuted choice tables - PC-1 and PC-2 - calculated for the DES block cipher algorithm?
4
votes
0answers
84 views

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 ...
1
vote
0answers
65 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 ...
1
vote
1answer
160 views

I wanna know what exactly SP array does

Please only look at for loop in source code below, especially SP1,SP2,SP3....... Is it similar to what S-box does?(Ignore the other) ...
12
votes
2answers
2k views

Why is DES not an ideal cipher?

From Cryptography I on Coursera, Week 2, "Exhaustive Key Search Attacks": Now let's assume that DES is what's called an ideal cipher [...] Of course, DES is not a collection of 2^56 random ...
1
vote
1answer
50 views

What (if any) information can an eavesdropper infer in this scenario when using DES in OFB mode?

Assume that a company wants to use DES in order to encrypt messages to remotely control its manufacturing machines. The company uses different messages types of 8 ASCII characters length each. The ...
4
votes
1answer
273 views

Show number of affected blocks using CFB DES decryption of altered ciphertext

I have encrypted a file using -des -cfb and now I want to view how many blocks it contains once I decrypt it. I have done this on the Linux terminal. I know that 9 ...
3
votes
1answer
420 views

DES: how does Richard Outerbridge's Initial Permutation operate?

I know how initial permutation works, but I've never heard of this part. People say it's Richard Outerbridge's initial permutation and that it's faster than usual IP (initial permutation) and simple. ...
2
votes
1answer
2k views

8-bit CFB in DES and AES - error propagation

I have two questions for an assignment that I need to answer in relation to Error Propagation in 8-bit CFB mode for AES and DES encryption. The questions are as follows: If there is an error in ...
0
votes
4answers
4k views

Can I find the encryption key if I know the plain text and the encrypted text (DES and AES)?

If I have the plain text and its output after encryption with a key K1, is it algorithmically feasible to find K1? I am specifically interested in the cases of DES and AES encryption algorithms.
0
votes
1answer
810 views

Finding output given an S-box input of 8 bits

I'm given the following table: I'm told to find the output given an hexidecmal input of 2B. I know that 2B in binary = 001 01 011 So I took the first two and ...