(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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3answers
4k views

What are the benefits of the two permutation tables in DES?

Why do we use a permutation table in the first step of DES algorithm and one at the end of algorithm?
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2answers
2k views

How were the DES S-box values determined?

It seems like the S-boxes in DES have essentially random values. How were these chosen?
13
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2answers
6k views

How long does it take to crack DES and AES?

Suppose that a single evaluation of a block-cipher (DES or AES) takes 10 operations, and the computer can do $10^{15}$ such operations per second. How long would it take for to recover a DES key, ...
11
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2answers
2k views

Why is MixColumns omitted from the last round of AES?

All rounds of AES (and Rijndael) have a MixColumns step, save the last round which omits it. DES has a similar feature where the last round differs slightly. The rationale, if I recall correctly, ...
11
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1answer
897 views

Duration for attacking Two-Key Triple-DES Encryption using all RAM ever built?

I am considering attacks on Two-Key Triple-DES Encryption assuming $2^{32}$ known plaintext/ciphertext pairs (that's a mere 32 Giga Bytes of ciphertext) by the method devised by Paul C. van Oorschot ...
9
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4answers
422 views

Should DES be avoided when developing new systems?

According to wikipedia… DES is now considered to be insecure for many applications However, since it can be broken relatively easy, should it not just be avoided for all applications?
6
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4answers
2k views

Is there any opensource white-box implementation of AES or DES?

I googled it and give me no result. There is a binary executable of white-box implementation of DES (scroll down), but no source code provided. The same page also links various papers about ...
5
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1answer
3k views

Why is triple-DES using three different keys vulnerable to a meet-in-the-middle-attack?

Among other sources, this wikipedia entry states that triple DES using three seperate keys (k1, k2, k3) is vulnerable to meet-in-the-middle-attacks, while triple DES using only two keys (k1, k2, k1) ...
5
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1answer
2k views

What are the details of the DES weakness of reusing the same IV in CBC mode with the same key?

I think I once faced the recommendation, that the initialization vector should always be random and never be used twice with the same key. How serious is this weakness? Also, is AES less effected ...
5
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1answer
3k views

Avalanche effect in DES

I couldn't understand the avalanche effect in DES. Could someone explain how avalanche effect happens in DES
5
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2answers
448 views

why DES uses exactly 16 rounds?

Why DES uses 16 rounds why not more or less then 16. what is the significant of using 16.
5
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1answer
173 views

DES key expansion: why are these two descriptions different?

I would like someone to explain me how to generate DES subkeys, because in the documentation that I saw, sometimes they say: "We rotate the initial key according to the number of iterations given ...
5
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1answer
239 views

S-box Cryptanalytic Resistance

In DES, different S-boxes were tested for cryptanalytic resistance and the most secure one was chosen for the algorithm itself. How do different S-boxes offer different levels of security against ...
4
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2answers
285 views

Increasing number of rounds in AES

AES-128 requires 10 rounds ( AES Description, Wikipedia ) However Bruce Schneier has recommended AES-128 use 16 rounds ( Schneier on Security: New Attack on AES ) Could that be implemented as two ...
4
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1answer
583 views

Linear Cryptanalysis

What is the principle of linear cryptanalysis, as applied to a block cipher ? For instance, this page gives the rough outline of differential cryptanalysis.
4
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1answer
157 views

Why no swapping block in the last round of DES?

Round 16 on the encryption side, and round 16 on the decryption side of DES have no swapping module. Why is it like this? Can anyone provide any justification? This is my homework question.
4
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1answer
181 views

How to choose keys for a block cipher?

AES and DES are block ciphers. Mathematically, its the mapping from plaintext space to ciphertext space using the keys i.e. $\{{0,1}\}^k$ x $\{{0,1}\}^l \longrightarrow \{{0,1}\}^l$ I know that these ...
4
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1answer
89 views

Has a Two Key TDES encryption ever been successfully attacked?

Is there any known instance of a Two Key TDES ever being successfully attacked (in real life), when the key is used to encrypt less than $2^{20}$ words?
4
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0answers
136 views

Reordering non-block-aligned parts with DES in ECB mode

I was given a ciphertext file which was encrypted using DES in ECB mode. It is known that the plainttext that was encrypted has the following form: Each line of text consists of a payroll followed ...
3
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2answers
207 views

DES — Can I recover the key when I have both ciphertext and the plaintext?

Given a message and DES encrypted form of said message, is it possible to efficiently compute the key used to encrypt the data?
3
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2answers
1k views

Decrypting DES with decrypted and encrypted data

I got two 8-byte strings. One which is decrypted is: FF FF FF FF FF FF FF FF and one which is encrypted is: ...
3
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1answer
533 views

Can you explain “weak keys” for DES?

A weak key for DES is a key $K$ such that $DES_{k_1}(DES_{k_2}(x))=x$ for all $x$. I don't get why are the 4 keys $k_1||k_2$: $1^{112}$, $0^{112}$, $0^{56}||1^{56}$, $1^{56}||0^{56}$ considered as ...
3
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2answers
373 views

Attacking 2DES efficiently

Meet in the middle on 2DES uses $2^{56}$ memory. Given the fact that the attacker has only $2^{45}$ memory. How can the attacker adjust the attack so even with this memory limit, it will still be more ...
3
votes
2answers
186 views

Have these compositions of block ciphers the same security?

I'm interested by the compositions of the block cipher DES, instantiated with independent keys $k_1$, $k_2$ and $k_3$. Are these 3 compositions equivalent in terms of security? ...
3
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1answer
654 views

Triple-DES Brute Force

Shannon's paper states: A system is pure if all keys are equally likely and if for any three transformations, $T_i$, $T_j$, $T_k$ in the set, the product $T_iT_j^{-1}T_k$ is also a ...
3
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1answer
799 views

ANSI X9.9 Cryptography Standards

I'm trying to create a ISO8583 Rev93 message. What is the standard way of generating MAC key in ANSI X9.9 DES-CBC encryption algorithm is used to encrypt the ...
2
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1answer
434 views

Can we replace the XOR operation in DES with some other operation?

Can we replace the XOR operation in the DES algorithm with some other operation? If so, does it work for both encryption and decryption?
2
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2answers
298 views

How can I encrypt more than 64 bit with the Data Encryption Standard?

The Data Encryption Algorithm is designed to encipher and decipher blocks of data consisting of 64 bits under control of a 56-bit key. If my data is more than 64 bits, (suppose 66 or 67 bits), will ...
2
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1answer
207 views

How insecure in practice?

I am in attempt to understand relative insecurity of certain encryption schemes. Particularly of interest is DES and RC2. I know AES is better and should be used to encrypt. But practically, if ...
2
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1answer
449 views

Meet-in-the-middle with checking complexity

In regards to meet in the middle type attacks, I have been considering the amount of operations in order to successfully find a key given two sets of plaintext / ciphertext pairs. All of the sources I ...
2
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1answer
128 views

Find out which keying option is being used in Triple DES?

As far as I know, there are three standard options for the three keys $K_1$, $K_2$ and $K_3$ used by 3DES: Three distinct keys. The first and last key are equal: $K_1$ = $K_3$. Three equal keys: ...
2
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1answer
102 views

Can you help me with this DES variant analysis?

I'm struggling with some DES variant that I got as an exercise (exercise taken from Katz-Lindell Ex5.14). The variant is as follows: The left half of the master key is used to derive all the ...
2
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1answer
263 views

AES with different modes of operation

I'm taking up a cryptography class and this is for an assignment. We're asked to find the differences between AES/RSA in the different modes of operation vs the one timepad method. From wiki, I can ...
2
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1answer
228 views

Regarding matsui's Paper on Linear Cryptanalysis of DES

I's going throught the the Paper by Matsui on Linear Cryptanalysis of DES . In that he says $NS_{5}(16,15)=12$ And then in the next paragraph he says considering the expansion and permutation phases ...
2
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2answers
463 views

DES Crack simulation

I wish to simulate an implementation of a DES Cracker using verilog. But every paper I read give only abstract hints but no concrete steps or how really to go about it. How is it usually done? For ...
2
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1answer
3k views

How does DES decryption work? Is it the same as encryption or the reverse? [duplicate]

If DES decryption is the same as encryption done in reverse order, then how can the reversed S-Box convert 4 bits into 6 bits?
2
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1answer
90 views

Is Triple-DES a group?

I know for a fact that DES is not a group, but are any of the Triple-Des versions a group? Why, or why not?
2
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1answer
95 views

Decryption or attacking DES encrypted file

I have a file that has been encrypted using DES and am looking to decrypt and find a secret message encoded. All I have is the file which is full of binary data. There is no key or anything else which ...
2
votes
1answer
261 views

DES Key Schedule Algorithm

Reading through the DES Specification it says that the keys are permuted with PC-1 initially and then shifted left both $C$ and $D$. However, before it gets ...
2
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1answer
1k views

Brute force attack on DES + property of DES

In a brute force attack on DES, it seems to me that one plaintext-ciphertext pair suffices to launch the attack. (I.e. suppose we are given a message $x$ and a ciphertext $c$ such that $DES_k ( x ) = ...
2
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1answer
594 views

Verilog simulation of Data Encryption Standard

I interested in developing DES(in verilog) for my college project.Can i get help in understanding the simulation results of DES encryption and decryption ? thanks in advance .
2
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1answer
86 views

Rotation table for 8 round DES

I'm trying to implement DES from scratch using the NIST paper and the Wikipedia article on DES. I got 16 round DES done, but I can't seem to get 8 round DES working. I figure it's because I got the ...
1
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1answer
2k views

Difference between linear cryptanalysis and differential cryptanalysis

What is the main difference between linear cryptanalysis and differential cryptanalysis? For example in relation to DES?
1
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1answer
583 views

Traditional DES scheme in Unix crypt function

In a security context course, we need to reproduce the old DES hashing scheme in the crypt program, on an old unix system. I am actually reading the crypt page on wikipedia: The traditional ...
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2answers
421 views

Cryptanalysis of S-DES - Equations

I am trying to derive equations for s and t in the cryptanalysis of a Simple DES algorithm, but I haven't been able to deduce ...
1
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1answer
3k views

c# Correct Triple Des Block Encryption Usage

I found the below code online, but in its original state, the encryption was not using any padding (Padding.None), and was encrypting in blocks of 8. I wasn't able to get this code to properly encrypt ...
1
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1answer
146 views

Exercise: Attack on a Two-Round DES Cipher

Working through the exercises in Cryptography Engineering (Schneier, Ferguson & Kohno) I have stalled on the following exercise: Consider a new block cipher, DES2, that consists only of two ...
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1answer
91 views

Does the key schedule function need to be a one-way function?

For some key schedule $e_n(e_{n-1}(k))$ (where $e_{n-1}(k)$ is the result of the previous round) , does $e$ need to be a one-way function? In the case of DES or Rijndael the key schedule doesn't ...
1
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2answers
278 views

How do we prove that AES, DES etc. are secure?

How do we prove that AES, DES etc. are secure? I've read about them and know the basics on how they work, but I still don't quite understand how we can be sure they are secure? What are the proofs?
1
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1answer
44 views

Perl DES PCBC as protection against decryption/crypt analysis

Is error propagation in DES PCBC a good method to prevent decryption/crypt analysis by third parties? If I had a very large file encrypted with Perl's DES with the PCBC option, and then removed the ...