Stack Exchange Network

Stack Exchange network consists of 174 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.

2
votes
1answer
58 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
70 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
81 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
850 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 ...
1
vote
0answers
40 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
53 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
69 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
62 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
48 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
82 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
90 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
133 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
138 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
133 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
123 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
104 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
132 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
66 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
339 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
178 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
51 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
174 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
45 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
412 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
46 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
165 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
78 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?
3
votes
0answers
74 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
156 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) ...
11
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
46 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
256 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
353 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
1k 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
2k 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
0answers
123 views

Davies-Meyer with DES insecure

I'm stuck in coming up with a collision for a hash function $H$, which is built using a Davies-Meyer construction chained in a Merkle-Damgard fashion. I I guess its actually easy using the fact that ...
0
votes
1answer
533 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 ...
0
votes
3answers
188 views

DES: histogram differences between plaintext and ciphertext

Using CrypTool I encrypted a plaintext with "DES CBC" and I genereated the histogram of plaintext and ciphertext. The histogram shows the relative frequency of each of the characters in the document. ...
0
votes
0answers
101 views

What values in the SDES algorithm change when we want to Decrypt?

So I am learning about SDES and I know how to use it to encrypt it. I know this is a symmetric algorithm which means it's basically the same thing to decrypt except a few things are reversed around. ...
0
votes
0answers
751 views

Triple DES encryption/decryption in nodejs

In Delphi , we are encrypting the password using TripleDESEncryption algorithm. We use the key as an array of byte [0..15]. Then the input string is converted is first saved to stream and then sends ...
5
votes
1answer
797 views

What is the main limitation of DES?

I know this question seems too general, not specific. Our professor asked this question today, and I have no idea how to answer it. Maybe it's the key size, maybe another thing? Any idea?
4
votes
1answer
149 views

Cracking truncated DES

Let's say we have a scheme in which 40 bits M are padded with 24 zeroes, encrypted using a secret DES key K, and the result truncated to the first 24 bits, C. If I wanted to determine a key that ...
4
votes
0answers
129 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, $C$ ...
4
votes
1answer
145 views

DES anti-fixed points for semi-weak keys

I am looking for some "real examples" of anti-fixed points for DES semi-weak keys. As I know, there are $2^{32}$ anti-fixed points for 4 of the 12 semi-weak keys each. One or two examples of these ...
0
votes
1answer
260 views

8th SharifCTF — What is the advisable way to recover the key of single round DES here?

I am participating in the 8th SharifCTF competition and have a related question: I have 1000 plaintext and its ciphertext, which has been encrypted with DES algorithm (only 1 round). Now, how can ...
0
votes
0answers
44 views

Find the Special DES key [duplicate]

I've given two pair of DES encryption plaintext-ciphertext as below: ...
0
votes
0answers
126 views

Why are binary operations used instead of S-boxes in the nonlinear F function?

Why are binary operations - such as AND, OR, XOR - used instead of S-boxes in the nonlinear F function? What would happen if a structure like the DES F function were used instead of the current ...
-1
votes
1answer
1k views

How 3DES work in a simple way?

As I understand DES, It encrypt 64-bit plaintext block with 56-bit key (ECB). So if ...