Cryptography

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(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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Best attack on double DES with XOR

Question: Assuming key k (56 bits), plain text P (64 bits), and cipher text C. What is the ...
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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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Vulnerability in DES3 when key can be chosen

In the question there are two functions encrypt basically does IV ⨁ DES3(P⨁IV) and encrypt_flag just encrypts the flag after being padded into a multiple of 8. IV is a random 8 byte number which is ...
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Reason for DES's inital permutation? [duplicate]

I'm learning DES, but I have a question. When the plain text input, it gets a permutation by a table. But, I don't know why 01 -> 58 / 02 -> 50. Is there any special rule or principle of it? or ...
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How to find Difference distribution table of DES S box?

I Have used Sage command ...
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Number of false keys in exhaustive key search for block ciphers

I'm doing a self study through Understanding Cryptography by Christof Paar and I have a question about Theorem 5.2.1 in the book: Given a block cipher with a key length of $k$ bits and block size of $...
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DES Encryption: Looking for results for each round of encryption/decryption to debug code

I've been searching for a few days in different forums trying to find an example of DES that gives the key/output values for all 16 layers. I found one that gives the encryption which helped me fix ...
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Problems with Matsui's Linear Cryptanalysis on round reduced DES

I'm trying to understand the known plaintext attack that is briefly explained in the paper Linear Cryptanalysis Method for DES Cipher by Mitsuru Matsui. I've almost understood it (since I'm ...
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OpenSSL DES encryption for KCV calculation

I'm trying to implement a simple command-line tool to calculate the (Key Check Value) KCV of some encryption keys. The algorithm for the KCV is simply to encrypt a block of 8 zeros with DES and get ...
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Can we design a block cipher based on SP-network without loss of E/D similarity theoretically?

I understand what SP-network (Substitution-Permutation Network) and Feistel Network look like. And those ciphers based on Feistel (e.g. DES) often achieve so called E/D similarity, which indicates ...
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RSA key requirements so that it can decrypt a DES key

I came upon a solved exercise that uses a client's RSA key to encrypt a DES key. It has the following phrase: value of n for RSA key generation has been chosen accordingly so that the DES key can be ...
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Where is the "Letter to NBS, October 22, 1975"

Discussions of the weakness of the U.S. Data Encryption Standard frequently cite a letter by Martin Hellman and Whitfield Diffie to the National Bureau of Standards that reported stated: Whit Diffie ...
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Known Plain Text Attack DES-OFB on Crack.sh

I am trying to do a known plaintext attack on DES-OFB through crack.sh. I have been having trouble lately. I keep getting blank text file back with no keys returned. Does anybody know if DES-OFB is ...
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How many collisions (identical pairs) are possible in meet in the middle attack on double DES with two unique keys?

I was reading my professors slides, I understand how meet in the middle works, but I have a few confusions. So we need two $\{(P_1, C_1), (P_2, C_2)\}$. Let $\lg{(k_1)} = \lg{(k_2)} = 56$, we generate ...
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Differential-linear attack on DES

Is there any known differential-linear attack on full round DES? I couldn't found any and couldn't work on this due to time restriction.
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Can we use Bitcoin miner to break 2Key 3DES, if yes how long it takes?

As ASICs are specifically designed to generate the hash for a block of a block chain. which is much faster than other GPUs which are used to break 2key-3DES. can we use Array of ASICs to break 2key-...
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Avalanche effect SBOX

It is possible to achieve the avalanche effect in an SPN or in a Feistel network that use a single round of an SPN in his function (like DES) using SBOX that receive 2 bit in input and output 2 bit?
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DES security if used a SHA3 function instead of Normal DES function?

I was practicing some python programming and I decided to implement a simple DES encryption function, so i decided to take some shortcuts so instead of DES expansion boxes and s-Boxes i just used a ...
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MAC forgery using the DES's Complementary Property

I've started reading on MACs and working on a problem where given a MAC construction as $H_0=IV$ and for every $i>0$ $H_i=H_{i−1} \oplus E_{M[i]}(H_{i−1})$ and the tag is $(IV,E_{k_1}(H_ℓ))$, I ...
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Getting to understand the linear approximation of DES

I will make a presentation about Linear approximation (Matsui's paper 1993 Linear Cryptanalysis Method for DES Cipher ) of DES and I don't understand some parts of it. Here my questions : In the ...
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Two Round Feistel network

While reading on block ciphers and DES I read that two-round Feistel network is not a secure PRP? Is there any easy to understand proof to explain the intuition behind this statement. I did search ...
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Converting normal alphabets to 64 bit plain text

How can I convert a normal alphabetical text (say hi) to a 64 bit or 128 bit binary digit input for DES?
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Is it possible to use an S-box similar to the one used in DES in AES? How would this work?

I'm reviewing some questions given to me by a professor and am stumped on this one. My initial guess is that yes, this is possible, but I do not know how to explain it, specifically for a function $\{...
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Is there any real attack deployed on the CTR mode over history?

The CTR mode, with its CPA security, is one of the malleable block cipher mode of operations. An attacker can simply modify the bits of the ciphertext stream in their advance. This is due to the lack ...
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Disrupting MITM attack against 3DES by intermingling plaintext and inter-mediate ciphertext between rounds

Let's say someone implements 3DES with three separate 56-bit keys and an attacker is attempting to execute a MITM attack. Here is the encryption plan designed to attempt to disrupt the MITM attack, or ...
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Proof that no DES key makes encryption identity

How can we prove that no DES key makes encryption the identity function? That is: $\;\forall K\in\{0,1\}^{56}\quad\exists M\in\{0,1\}^{64}\quad E_K(M)\ne M$ Note: anyone disproving this proposition ...
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DES : Is Double Encryption using same key twice equivalent to single DES using different key but of same size

If we encrypt a plain text using Double DES but with same key K1, Can we get the same result as if we would encrypt the plain text using single DES but with different key, say K2. What I'm asking is ...
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How to find Key with DES, ECB hash and plaintext [closed]

I have two ciphertexts. Encryption algorithm: DES in ECB mode. Ciphertext: 72EE3532F904CE2AAA966C723C463F294CA8AB1C11E9E0B304BBB6A8E2BD1F34 Plaintext: DetectedSpambotsRemailedMalwares Ciphertext: ...
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How to calculate size of a codebook lookup table to break block cipher?

I was reading a book called Serious Cryptography. There is a page saying that block size must be large enough to prevent codebook attacks: When 16-bit blocks are used, the lookup table needs only 2^...
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ISO 9797 MAC algorithm 3 for 7 bytes

I should implement ISO 9797 MAC algorithm 3 with initial transformation 1, without truncation, and using DES as a block cipher. I should add padding of 0x80, then ...
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"16-bit DES encryption algorithm"

I need to use encryption software from PSpice for my SPICE model. In a user guide on page 71 they claim to use a "16-bit DES encryption algorithm". According to the wiki DES is using a 64-...
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261 views

Quadruple DES vs AES-128 security

I came across this question regarding the security of Quadruple DES (hypothetically DES done four times) in CBC encryption mode vs security of AES-128 in CBC encryption mode. What parameters help to ...
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DES decryption of the homomorphic encryption ciphertext

I implemented an application using partial homomorphic encryption for outsourced computations. To get an efficient bandwidth, I am thinking to apply (DES) symmetric algorithm to encrypt the message ...
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Frequency Analysis on DES, AES, 3DES using Cryptool2

I am trying to analyze symmetric block ciphers like DES, 3DES and AES, using Cryptool 2. I want to do a frequency analysis on each of these ciphers, in order to comment whether this is an effective ...
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Attack against $\operatorname{DESA}_{k,k_1} (x) \underset{\text{def}}= \operatorname{DES}_k(x)⊕k_1$

Problem 5.16 in this pdf, from the book: Christof Paar, Jan Pelzl, Understanding Cryptography 5.16. This is your chance to break a cryptosystem. As we know by now, cryptography is a tricky business. ...
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Prove how to brute-force the double encryption with complexity 2^57 rather than 2^112?

We know that DES has key length that is too short to defend brute-force attack. One idea to improve DES was to encrypt a message using DES twice with two different keys. Let E be the encryption ...
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DES f function injective for no fixed subkey?

Let $f$ be the function used in a round of DES, as defined in FIPS 46-3: $$\begin{align} f:\{0,1\}^{32}\times\{0,1\}^{48}&\to\ \{0,1\}^{32}\\ (R,K)\ &\mapsto f(R,K)\underset{\mathsf{def}}=...
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DES F function never injective?

Now i know that the F function doesn't have to be injective, but is it NEVER injective? or is it possible to have an injective F function?
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How to determine the maximum number of times the DES algorithm needs to be run?

I am only a beginner in cryptography and I am getting confused by the following: Question Consider a known-plaintext attack performed on a double-DES cryptosystem. (a) Determine the maximum number ...
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Proof of probability of weak keys in block cipher

My textbook has the following theorem: Given a block cipher with a key length of K bits and blocksize of n bits as well as t plaintext-ciphertext pairs, the expected number of false keys which ...
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DES Meet in the Middle

My professor showed us the basics of DES, and then displayed this slide where the Meet in the Middle attack can be used as a way of cracking DES. I believe at this stage we are doing 2DES, as opposed ...

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