# Questions tagged [cryptanalysis]

Analysis of individual security aspects of a cipher or algorithm, not the security of a cipher or algorithm in general (which would lean towards “algorithm-design”).

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### Efficient way of knowing large factors of $\phi(n)$ given small prime factors and $n$

Knowing large prime factor$(r > n^{1/4})$ of $\phi(n)$ can easily factorize n and hence learn $\phi(n)$. If we have knowledge on all small prime factors $(2< r_i << n^{1/4})$ of $\phi(n)$...
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### Strict Avalanche Criteria in Sage

Is there any inbuilt functionality in sage to check if any S-Box satisfies Strict Avalanche Criterion or not?
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### Using XL Algorithm to solve overdetermined systems, simple example required

Can someone give an example of how the XL algorithm is used to solve an overdetermined system as apposed to just a general case? I have a fairly good understanding of how steps of the algorithm work, ...
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### Does secure LWE implementation leak bit information?

We know RSA leaks one bit about the factors and improper yet secure implementations of Discrete Logarithm leak one bit about the discrete logarithm. Does LWE leak any information?
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### Known Plaintext Attack A5/2

I am trying to understand the non-optimized known plaintext attack on A5/2 from Barkan, Bikan and Keller. I don't understand the construction of the equation system: $$S_{R4_1} * S_1 = k$$ Where $S$ ...
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### How can I identify the linear equations for a block cipher with 4 different s-boxes?

For a block cipher with 4 different s-boxes (each used in an individual round) how can I identify the linear equations? Normally, for ciphers like AES with a single s-box, linear cryptanalysis can be ...
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### Why the permutation of the right hand rotor given in Rejewski's paper is $PNP^{-1}$?

I would like to know why the permutation of the right hand rotor given in Rejewski's paper is $PNP^{-1}$. First of all I can't get how he added an $P$(alphabetic permutation) at the front of $N$(...
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### List of security protocols that have been proved to have bugs using formal methods

I'm looking for articles about finding bugs in security protocols using formal methods so I can test them using tools like proverif I've searched a lot of references but most of them seem to be about ...
534 views

### Cracking a key using a combination of partial keys

As part of a cryptanalytic attack I've carried out, I used a divide-and-conquer strategy to divide the secret key $k$ into several equal-sized partial keys $k = {k_1, k_2, ...}$. The attack works ...
35 views

### Explanation of the generalisation of multiset properties to a concatenation of a block

I am trying to learn about SASAS cryptanalysis. I am reading the paper related to this where the authors use multisets are used within the cryptanalysis of this cipher. I did not understand the part ...
136 views

### Get LCG from output?

Given a standard LCG output, let's say 3 consecutive numbers, I'm wondering how I could get $a$ and $c$ if I already know $m$ LCG formula: Sn+1 = ( aSn + c ) mod m I've seen this posted in a lot of ...
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### Infer encoding mechanism from $n$-grams distance?

I have a series of obfuscated strings which across the set of strings have regions of high variance and regions of low variance – implying some encoding mechanism as opposed to an encryption procedure ...
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### Cracking an appliance's network protocol

I'm trying to crack my thermostat's network protocol. I've captured several rounds of network traffic and here is what I've got to work with. Communicating via HTTP POST The POST data is JSON ...
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### Why the same characteristics cannot be used to recover all FEAL4 keys

I am trying to understand how differential Cryptanalysis works. Here I read how to use differential cryptoanalysis for cracking FEAL4 cipher. The big gotcha with this process is that you cannot ...
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### Applications of machine learning in classical ciphers?

Machine learning is definitely applicable in analyzing simple shift ciphers like Caesar and affine ciphers, as well as substitution ciphers like Vigenère, but is it possible for machine learning to ...
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### In DES : Matsui's notation(LC) vs Biham's notation(DC)

I'm doing linear attack for 8 rounds DES. And I just wondering about the difference between Matsui's notation and Biham's notation. In Matsui's paper, numbers bits from 0 to 63 from right to left. In ...
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### Finding repeated groups of letters in the Kasiski examination

While doing the Kasiski examination I came to a problem. If there is the following group of letters in the cipher: AA and later on a group AAA is found. Does it count as two repeats or just one? And ...
44 views

### Are slide attacks effective if the primitive is sandwiched? And key schedule vs. Even-Mansour

Suppose you have a cryptographic permutation consisting of identical rounds, that makes it vulnerable to a slide attack. But if you sandwich it between two XORs of key material. Is it still vulnerable?...
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### How can I guess that a combination of Atbasch and Caesar / Vigenère has been used?

If I'm given a ciphertext, what kind of patterns, index of coincidence, frequency analysis would lead me to guess that it had been encrypted by a combination of Atbasch plus Caesar / Vigenère?
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### Guess the number of characteristics in differential cryptanalysis

I am doing some research on differential cryptanalysis for my master thesis. I analyzed some toy ciphers like the one in the popular tutorial about differential and linear cryptanalysis from heys Link....
133 views

### zero knowledge proof of range and set membership

I have a large number of items with a unique serial number and a score (score isn't always unique). There is a list which contains all of the serial numbers and their respective scores. I select 3 ...