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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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1 answer
102 views

Finding out corrupted S Box value in DES implementation?

I am using DES encryption when writing a file in an embedded device. When I decrypt the file. I get a partially corrupted file. Kind of randomly some 8-byte blocks are corrupted. Some are not. When I ...
2 votes
1 answer
123 views

Proving DES complementation property: y = DES(k,x) ⟹ /y = DES(/k, /x)

Below is my proof for this. I was not sure if this is correct and was also a little confused regarding the complementarity property of DES. Does this property mean there is a serious vulnerability in ...
45 votes
3 answers
39k views

Is Triple DES still considered safe to use?

What it says on the tin. Is it still used in things like TLS?
2 votes
2 answers
122 views

Using the MAC to verify if Cipher Only attack has succeeded

I am working on an experiment to compare the efficiency of brute-force attacking block ciphers like AES and DES with reduced key sizes for different programming languages and library implementations. ...
6 votes
2 answers
2k views

Are there any other applications of machine learning to cryptography?

I've checked a bunch of articles about machine learning and cryptography and derived from them three distinct possibilities: Use ML to approximate a cipher as a function. Article "Neuro-Cryptanalysis ...
0 votes
0 answers
33 views

Showing if y=DES(k, x), then /y = DES(/k, /x) [duplicate]

The textbook gives a similar example of proving the below problem: Based on this, how would I go about showing $y={DES(k, x)} => \overline y=DES(\overline k, \overline x)$, within the same format ...
2 votes
1 answer
2k 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 ...
3 votes
1 answer
199 views

Is DES/2DES/3DES still used?

I checked a related question, but I still did not find the answer I was looking for. Specifically, do we have any statistics on the usage of DES/2DES/3DES? It seems from here that credit card systems ...
21 votes
1 answer
24k 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 separate keys $(k_1, k_2, k_3)$ is vulnerable to meet-in-the-middle-attacks, while triple-DES using only two keys $(k_1, ...
2 votes
3 answers
1k 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 ...
0 votes
1 answer
82 views

How is it that the attack in this pdf is deemed feasible, at 2 to the power of 88/89 des calculations?

in the following pdf, several attacks on double key length triple des are deemed feasible at 2 to the power of 88/89 des calculations. if we take the record of cracking des at 2 to the power of 56 ...
5 votes
2 answers
8k 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 ...
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0 answers
118 views

Finding bit positions of '1' in DES Encryption

In DES encryption, the IP table is shown. If the input given in hexadecimal is "0020 0940 0000 F008", which are the bit positions of "1" after the IP stage ?
2 votes
3 answers
4k views

DES Encryption Algorithm all 64 bits for key instead of 56 bits

Would a DES algorithm that uses all 64 bits for the key instead of just the 56 bits be more secure? I have been thinking about it but those 8 bits used for parity are very useful and but including ...
19 votes
2 answers
3k 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 ...
0 votes
1 answer
141 views

Initial Permutation in DES

Why is the Initial Permutation Step necessary in DES? How does it strengthen the cipher since we are reversing the permutation in the output?
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0 answers
330 views

MDK vs IMK vs MK key differences

I don't understand whether they are different or not. Would you mind explaining them all? MK-AC, MK-SMI, MK-SMC MDK Encryption Key, MDK MAC, MDK AC IMK-AC, IMK-SMI, IMK-SMC For example, in the ...
2 votes
1 answer
994 views

CTF - DES Challenge

I am trying to solve a CTF challenge based on DES. I attached the code of the challenge to the question. So far I have noticed that the otp used for the encryption is the same for the entire session, ...
0 votes
1 answer
81 views

How Does S box introduce diffusion in DES?

According to a Lecture from Lecture notes of a Professor of Purdue University "Diffusion means that a change in any plaintext bit must propagate out to as many ciphertext bits as possible." ...
2 votes
0 answers
39 views

How many ciphertexts should attacker intercepts if he only knows the first 3 bytes of plaintext of each one?

Consider a system in which DES is used to encrypt messages in which the first three plaintext Bytes are known by the attacker. How many encrypted messages is it necessary to intercept in order to be ...
1 vote
1 answer
150 views

DES attack with known partial plaintext

Consider a system where DES is used to encrypt HTTP GET requests. The first three bytes correspond to the character sequence "GET". How many encrypted messages is it necessary to intercept ...
1 vote
0 answers
607 views

DES in cipher feedback mode CFB

We use DES in cipher feedback mode (CFB) to encrypt a plaintext $m = m_1\mathbin\|m_2\mathbin\|\ldots\mathbin\|m_{100}$ into a ciphertext $c_1\mathbin\|c_2\mathbin\|\ldots\mathbin\|c_{100}$, where ...
2 votes
2 answers
434 views

Why do we encrypt then decrypt then encrypt data with different keys?

In GlobalPlatform specification for smartcards, I came accross this rather strange scheme* ISO/IEC ISO/IEC 9797-1 MAC Algorithm 3: To calculate the Message Authentication Code, we take some original ...
2 votes
2 answers
78 views

DES initial key generation

I am working through a textbook on crypto, currently on DES section. What bothers me is that there was no explanation about where do we get initial 64-bit key from. This question is also very hard to ...
1 vote
1 answer
139 views

Increasing the parallelization of Triple-DES

Triple-DES encrypts with the first key, then the second key, then the third key. Two keys are sitting around waiting. Why not encrypt with all three keys at the same time? You take 192 bits of ...
0 votes
0 answers
631 views

Cracking 2-Key Triple DES

I've been given that an attacker has a 2-Key Triple DES Cracker that is capable of performing 10$^{24}$ encryptions per second and have subsequently been asked how long it must take before the ...
-1 votes
1 answer
433 views

How is DES used with CBC?

I'm reading our school's notes for cryptography, and it does a good job explaining CBC and DES in detail, but it fails to provide good information on how they are related. From what I've researched so ...
0 votes
2 answers
63 views

Attack on AES/DES [duplicate]

Can we devise an attack on AES or DES (ECB mode) if we know just the distribution for the plaintext? For example, it is a English plain text -- we know what that would look like and the relative ...
1 vote
0 answers
69 views

DES next round key

I don't understand which DES key is used in the next round of Feistel construction. As you can see below, we use our original key that has been inserted in permuted choice 1, where we got 56 bits, ...
1 vote
2 answers
883 views

(DES) What is the probability that two keys (k1, k2) produce the same ciphertext given the same plaintext?

Basically, I need to find the probability that DES(p, k1) = DES(p, k2) = c My guess is that probability = 1 / 2^64 since that's the total number of possible outputs, but honestly I have no clue about ...
0 votes
1 answer
58 views

2DES has an identity key - clarification

In this post, there's a discussion on single DES not having a key that yields the identity function. It mentions at the top: That proposition is false for 2DES (EE), even restricted to one key, ...
0 votes
0 answers
44 views

Is the following attack on a DES-based commitment scheme valid?

I've encountered the following question while practising for an upcoming exam in Cryptography and would like to know if I'm on the right track: The following is a suggestion for a DES-based ...
0 votes
1 answer
95 views

Equivalance of encryption and decryption in DES under bruteforce

I am studying the vulnerability of DES algorithm. Let there be a DES system with 5 keys, 56bits each. Encryption works as follows: (It's in this order on purpose) $C=DEC_{k1}(ENC_{k2}(ENC_{k3}(DEC_{k4}...
-1 votes
1 answer
146 views

What is the importance of superencryption?

Please, can any extensively explain the importance of super encryption in relation to attacks experienced by single standard algorithms
8 votes
2 answers
1k 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{...
7 votes
3 answers
6k views

What is DES-EDE3-CBC?

I came across DES-EDE3-CBC and a quick search didn't yield a clear explanation of what it is. Clearly, DES is the Data Encryption Standard and CBC is the Cipher Block Chaining mode. EDE is probably ...
3 votes
0 answers
77 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 ...
3 votes
1 answer
1k 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. ...
3 votes
0 answers
164 views

What are the concrete changes the NSA did to the algorithm before DES was published?

It's common knowledge that the NSA, before publication of DES, tweaked the algorithm to improve its resistance against differential cryptanalysis. Schneier writes some of this on his blog, for example ...
4 votes
1 answer
524 views

Matsui's linear attack on 5-round DES

I'm trying to understand Mitsuru Matsui's "Linear Cryptanalysis Method for DES Cipher", specifically the attack he describes at the end of section 5, on 5-round DES. I followed the attack on ...
1 vote
0 answers
316 views

Variant of DES and breaking the 16 round DES

Consider a variant of DES algorithm, called DES-WEAK. In DES-WEAK, there is no permutation P in a round and all the S-boxes are replaced. The new S-boxes are all identical and defined as follows. Let ...
1 vote
0 answers
51 views

How does one produce this in the linear cryptanalysis of DES

I understand how this linear approximation board below is produced, but I can't understand how this second board is produced using the first one and finally how the pilling-up lemma values are ...
5 votes
1 answer
4k 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?
2 votes
1 answer
276 views

DES SBOX Output with Bitslice

I am not understanding how to compute the output bits of a 6-to-4-SBOX with bitslice technique in DES. Matthew Kwan made a brief recap in his paper "Reducing the Gate Count of Bitslice DES" ...
0 votes
0 answers
36 views

Evaluation of prediction of probability is a DES structure

Suppose you are given $DES_k(m)$ for some unknown $k$ and $m$, where DES() is the usual DES scheme. With what probability can you predict, for example, the 12-th bit in the output of $DES_{\bar{k}}(\...
1 vote
1 answer
1k views

How to solve this S Box?

I have performed the XOR and the result comes as 1001. Now my confusion is that in standard S-Box (DES) the input is 6 bit where the first and last bit together specifies row and 4-middle bits column. ...
1 vote
1 answer
697 views

Which block cipher modes are best used in real life situations?

For an exam I'm studying for, I'm wondering what block cipher modes are best to use in certain situations. We learned about these block cipher modes: ECB, CBC, CFB (+ s-bit), OFB (+ s-bit) and CTR. ...
8 votes
1 answer
1k 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 ...
0 votes
1 answer
64 views

Security in a pipeline

I am new to cryptography, I am trying to design a secure pipeline environment for the fast transfer of messages. To reduce the Key size I am planning to encrypt the messages with AES session keys (for ...
-1 votes
1 answer
414 views

How to make DES more secure without switching from des state to another cryptography system and what are limitations of DES?

How to make DES more secure without switching from des state to another cryptography system and what are limitations of DES? Is there any 3 ways to make des more secure?

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