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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Finding generator element for multiplicative group of order $n$ - feasible?

Given a multiplicative group of order $n$, how hard is it to find a generator element (such that all other elements can be expressed as powers of that generator)? What would be the complexity?
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Question on nCPA Security and Uniform Permutations

I feel I am misunderstanding the idea of nCPA security and its relation to uniform permutations. In particular I've been reading the paper "Hoang, Morris Rogaway; An Enciphering Scheme Based on a Card ...
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130 views

Mersenne Twister's vulnerabilty with small-size distributions

C++ rookie here, trying to wrap his head around (CS)PRNGs. I (assume that I) already understand the concept of the Mersenne Twister being "broken" (i.e. not cryptographically secure) due to its ...
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Preserving location privacy

What are cryptographic techniques that could be used so that if I wanna to enable a server to send message to certain nodes in a network with preserving the privacy location for them ??
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451 views

Cryptanalysis affine cipher and substitution cipher

1) Consider the chosen-plaintext attack on the simple substitution cipher. How many chosen plaintext characters suffice to uniquely determine the key? My answer was: 26! 2) Consider the chosen-...
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149 views

Leak information (new setting)

This question is similar to Leak Information?, but with new settings. Let $a,b,c,d,e,f$ be selected at random from $\mathbb Z^*_q$. Also, let $r_1,r_2,r_3,z_1,z_2,z_3,p_1,p_2,p_3$ be selected at ...
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67 views

Can I deduce the info such as the bitsize of an LFSR from multiple ciphertext messages?

If I encrypt the same message multiple times (>10000 times) with the same LFSR can I then somehow retrieve some information on the LFSR? I'm looking for information like bit size, polynomial used. The ...
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81 views

What is the attack complexity if two stream ciphers are connected in cascade?

What is the attack complexity when Grain-128 and Trivium are cascaded? Is it 2^(256 + 128) since internal state of Grain is 256 bits and assuming that IV is unknown before encryption?
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A name for “word fingerprints” (technique for breaking monoalphabetic substitutional ciphers)

I have invented a technique for breaking monoalphabetic substitution ciphers. However, I believe that such simple thing must have been already invented. I wonder how is this called. I call it “word ...
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1k views

RC4: Find the complete plain text of a ciphertext when we know part of the plaintext

I need to decrypt an encrypted file with RC4 to answer to a Internet challenge. The file in question is a dump of a Teensy ROM and it is completely encrypted. Luckily, it looks like it's a standard ...
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What weak symmetric cryptographic algorithms shall I use to educate myself about cryptoanalysis methods?

Are there any simple to understand and implement, but nontrivial cyphers and hash functions which are easily broken by modern cryptoanalysis methods (for example, ones listed in Wikipedia)? Ideally ...
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736 views

Known plaintext attack against Feistel ciphers

Assuming we have a Feistel cipher, with let's say 2 rounds i.e: Plaintext $P=(L_{0},R_{0})$ $L_{1}=R_{0}$ $R_{1}=L_{0}\oplus f_{{K}_{1}}(R_{0})$ $L_{2}=R_{1}$ $R_{2}=L_{1}\oplus f_{{K}_{2}}(R_{1})...
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Why in the Rao-Nam private key version of McEliece scheme, P matrix is multiplied after adding error vector?

The private key version of McEliece known as Rao-Nam scheme, the encryption is done as c = (mSG + e)P. What is the need for applying permutation matrix on the error vector?
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128 views

Attack on Cipher with Highly Related RoundKeys

Consider a variation of AES with modified Key-Schedule and following observation on the Key Schedule. If there exists a relation d between two Master keys, the key schedule is so weak that all sub-...
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342 views

truncated linear congruential generator

I'm trying to reverse a truncated linear congruential generator with all parameters ( modulus $M,$ multiplier $a$, addend $b$ and the seed $x_0$) hidden. I have read Scott Contini's article On ...
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53 views

Fuzzy Extractor: Order of elements in set

Does order of elements in two sets matters to authenticate using Fuzzy Extractor? Using extractor as proposed in https://www.cs.bu.edu/~reyzin/fuzzy.html it seems the set difference is zero for this ...
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92 views

Can I attack a PRNG using a differential or linear cryptanalysis?

I modified the generation key function of XTEA using a PRNG with 128 bits. I have to attack it using both differential and linear cryptanalysis but I don't see how, it's possible to attack a PRNG?
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Converting discrete log problem to a multivariate system of equations

Is there any method of converting a discrete logarithm problem to an equation system, such that the solution of the system corresponds to the solution of that instance of DLP?
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47 views

How many operations per key for partial character matching?

Given a substitution cipher having a key with n alphanumeric characters, if an attacker knows p characters in the key, how many operations per key are required by his computer to compare a permutation ...
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279 views

Algebraic Attacks against ARX

I have not seen much about algebraic attacks against ARX ciphers. How would ARX ciphers compare in algebraic security to AES or Present or Simon?
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45 views

How to calculate how many trials I need to guess the plain text if a simple P-Box is used to make the cipher text

If I have 64 bit as input for a straight box that use a transposition process to encipher the plain text and the given 64 bits contains 60 bits as (1s), then how many trial I should do?
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149 views

Issue Factorization Quadratic Sieve

Good evening, I'm about to write my own quadratic sieve implementation in C using GMP library for large numbers. I'm facing an issue while attempting to do the last factorization step for the number: ...
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66 views

Can error correcting codes be used to guess this plaintext?

I pick a finite set of messages, perhaps the set of integers $M = \lbrace n \in \mathbf{Z} \, : \, 0 \leq n\lt10 \rbrace$, which you are then allowed to encode in any way you want (some form of error ...
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560 views

Is it possible to create a detection oracle for all block cipher modes? — ciphertext-only cryptanalysis

I have made an ECB/CBC detection oracle, and am now trying to make a detection oracle that can differentiate between CBC/CFB/OFB/CTR/etc. I can already tell ECB apart from the others due to this ...
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821 views

Breaking Vigenere via Kasiski/Babbage method? (non-programmatic)

I'm really hoping someone can explain to me what is going on in the second major component of this form of analysis. If you wish, for convenience, here's a page that already has some ciphered text ...
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106 views

Encryption technology for DARPA

I'm working on a short story taking place in the near future in which a hacker gains access to the DARPA mainframe and files related to a highly classified DARPA project. Being ignorant about state ...
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294 views

Calculating Phi(M) and D for RSA decryption given p,q,e

I've been given a message in 4 digit numbers but it doesn't seem to work when I use my calculated values for phi(m) and d. If I'm correct phi(m) = (p-1)(q-1) correct? And d is given by ed = 1mod(phi(m)...
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38 views

How to calculate LOW(b) and HIGH(b) in spritz cryptography

I try to implement spritz cryptography like this paper . But I don't know how to calculate LOW(b) and HIGH(b). In paper page 7. ...
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144 views

Security of a custom non linear hill cipher

Initially let me state that this is an atypical type of cryptographic encoding. First I break up my key into three parts $k = {W,\overrightarrow{b},\alpha}$. the $W$ is simply a $n \times n$ matrix, $...
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197 views

RSA OAEP: prevention of partial decryption of ciphertexts

I'm trying to understand RSA encryption (as a beginner in cryptography). go on this wiki page http://en.wikipedia.org/wiki/Optimal_asymmetric_encryption_padding scroll down to the 2 numbered points: "...
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To prove $r_2$ is a uniformly at random value in $Z_n$, where $r_2=r_1 . m$

$m$ is arbitrary value in $Z_n$, where n is RSA modulo. Then we do: $r_2=r_1 . m (modn)$, where $r_1$ is a random value such that $r_1\in Z^*_n$. ** Question(1): is $r_2$ a uniformly at random ...
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Cryptography — with a semi-priveleged user in the middle — to prevent request-tampering with another server

I'm working on a chat server for a mobile app I am writing. I would like to use a different application server for non-chat related operations and another application for chat operations. I would ...
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45 views

Decryption of an unknown cipher

How can I identify the cipher that encrypted the data shown below? I'm very new to this field, so I am not sure. For example: How does one know which cipher is used in the following line? How can one ...
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63 views

Which contemporary programming language is apt for implementation of algorithms in cryptography?

I am a researcher in cryptography. Most of the time I generally do theoretical/Mathematical work only and not doing the implementation part. I am not able to get the feel about the time complexity of ...
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28 views

A few questions regarding the 4-Round AES-Distinguisher (by Gilbert and Minier) and DS-MITM

I am struggling to understand the DS-MITM attack on AES (Original Paper). Especially the 4-rounds distinguisher by Gilbert and Minier (section 3). I get the basic idea that we check exactly on which ...
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32 views

Decrypt encryptedKey session key using - AES-128 - PKCS-1#rsaes-kem-kdf2-kw-aes128

I have basic knowledge about how encryption algorithms work such as RSA, AES and so on. I have an XML response encrypted with both AES and RSA. I tried using OpenSSL to decrypt with several steps but ...
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Few questions about setting up SuperCop primitives

Have a couple of questions about the supercop library. I've refrained from asking this question for a considerable amount of time because every time I thought about asking it, it sounded stupid in my ...
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54 views

Cryptographic Principles: Bit-Flipping Attack

I'm working and reading about bit-flipping attack and how to set it up. I just got a question, which I am not sure, how I should answer. Question: 'Why is this easy with a stream cipher but not ...
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35 views

Difficult to guess the targeted receiver

The protocol is defined as : Bob want to send message to one of his friends say $k$ friends , he does not want his others friends (except one whom he want to send message ) to tell who is targeted ...
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28 views

How to find Difference distribution table of DES S box?

I Have used Sage command ...
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I was going through Path ORAM in oblivious RAM. I found it very interesting, as its promising but is there any scope left to enhance it?

Is there any specific field in Path ORAM where I can further investigate or research?
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How do I model this system?

I was trying to work out the security of an system that used the polarized LCD panel over an OLED display (the point being that you can only block certain pixels) and the pixels are either on or off (...
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In the reduction proof below, where OWF exists only if is a PRG. I am not able to understand the highlighted part

I am able to understand how G(x) id generated. But then what is the use of variable z. Also if the probability is >1/2 + e then the distinguisher wins! Then how is this still a OWF
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Identify encryption scheme - Many-To-One?

What type of encryption is used when the encrypted phrase only uses the letters from a keyword? For Example: Keyword: Stack tkc ska ktkkac skccaasca ckssak This was encrypted using only the letters ...
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Fundamentals of XL algorithm

I am trying to understand XL algorithm and F4/F5 algorithms for solving multivariate polynomial systems. Is XL related to the Grobner basis? I would be grateful if anyone could suggest me the topics (...
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87 views

One-time pad: Using Cribdrag for Decipherment and Key Recovery

I have been given three different strings: ...
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Reversing black box algorithm

I'm trying to solve the next problem: We have X - input vector, its length is 128 bits. Output vector Y, its length 2048 bits. ...
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27 views

Is there a LPN estimator like LWE?

I recently studied the LPN problem and BKW algorithm for solving LPN problem. Several papers deal with the concrete parameters of LPN to be secure against BKW algorithm, but I cannot measure the ...
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How is the second digram a legal mapping? (Playfair Cipher)

So this is a partly completed key I have: _ R _ _ _ _ T _ _ _ _ _ H _ _ _ _ L _ _ _ P _ _ W And this is my plaintext/ciphertext: ...
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59 views

Cascading encryption with blocks or output

For educational purposes, I'm trying to build a cascading encryption implementation with AES, Twofish, Blowfish, Salsa20, and ChaCha20. First of all, please don't judge my paranoia or choices, this is ...