# 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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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ?
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### 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. ...
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### 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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### 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 ...
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### 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 ...
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### 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 ...
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### 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, ...
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### 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." ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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, ...
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### (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 ...
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### 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, ...
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### 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 ...
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### 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. ...
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### 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. ...
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### 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 ...
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### What are those RSA Challenges, DES Challenges and RSA Factoring Challenges

Can someone explain the differences between the DES challenge, the RSA challenges, and the RSA factoring challenge? What were the aims? I think the factoring challenge was to encourage research, the ...
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### 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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### Why are des-cbc-hmac and rc4-hmac-exp considered weak in kerberos?

Kerberos uses des-cbc-hmac (mac and encrypt) and rc4-hmac-exp based on md5 (mac and encrypt I think) in their encryptions. Those encryptions are considered as weak and should not be used. Why are they ...
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### Meet in the middle time complexity

Hello, I am wondering why it is stated that double encrypted message with 2 DES keys is possible to break in worst case in $2\times2^{56}$ time using meet in the middle attack. Here is my reasoning: ...
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### An algorithm to break 2DES with less operations than exhaustive search

Exercise 3.6 from Cryptography and Engineering Consider a new block cipher, DES2, that consists only of two rounds of the DES block cipher. DES2 has the same block and key size as DES. For this ...
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### What are the minimum mathematics and computer science subjects that I need to understand DES and AES?

I want to study the DES and AES algorithms The question: What are the minimum mathematics and computer science subjects that I need to understand DES and AES? Edit: I mean how they work internally.
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### How Differential Cryptanalysis of DES work?

I have been studying the DC of DES. As a beginner, I completed the general structure of DES and began DC. I understand the idea of attack, how to find different characteristics for differential ...
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### PRNG For RSA (ANSI_X9.31)

I have a query please , I want to know how to generate random numbers using ANSI_X9.31 algorithm for RSA Algorithm please . Thank u
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### How to generate keys from a 56 bit using DES

First I just want to apologize for my lack of knowledge in this system. The professor kind of gave us an exercise to solve before even going through the lessons. I tired to look at videos online but ...
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### Formal security arguments for 3 round feistal network using PRF

There is a proof sketch in Introduction to modern cryptography that a three-round feistel network using pseudorandom round functions is a secure pseudorandom permutation PRP Πk against probabilistic ...
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### Why is this DES key considered weak?

I understand the premise of weak keys in DES and cryptography. From searching online, I understand that keys that are comprised of all zeroes / all ones / alternating ones and zeroes / alternating ...
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### Why is a Feistel Network invertible?

As it is depicted above, the Feistel Network uses random function fi which is not required to be invertible. However, if fi is not invertible, how can fi(Li) == fi(Ri-1)? Furthermore, why Feistel ...
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