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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Acceptable condition for dictionary search

I am trying to write a program to break transposition cipher using dictionary search. But I cannot understand the finishing condition of the search. Is there any theory that the maximum number of ...
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25 views

In NTRU digital envelope, do everyone know the hash function $H$ used?

I have a simple question about the NTRU original cryptosystem using a digital envelope. The article can be found here: http://grouper.ieee.org/groups/1363/lattPK/submissions/ntru.pdf It is said that ...
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Mitigating weaknesses in RC4 [duplicate]

I've been researching RC4 and implementing it, and I was wondering, from the perspective of a cryptographer (a real one, not a fake one like me), what could be added to the RC4 algorithm to improve on ...
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72 views

How does one practically calculate the non-linearity of a multi-output boolean function like the AES s-box?

I am working on multi-output boolean function i.e. a function that takes an $n$-bit input and gives an $m$-bit output for all possible inputs (i.e. $2^n$ inputs). To be more exact: I am trying to do ...
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74 views

Problem with LLL reduction on truncated LCG schemes

I am struggling to apply Freize et al. paper to break a truncated LCG. A truncated LCG is a pseudo random generator that outputs the $n$ leading bits $y_i$ of $x_i$, where $(x_i)$ is such that $x_{...
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63 views

How to create reduction functions in rainbow tables?

I have been trying to understand rainbow tables lately and one part is giving me trouble to understand here. Let's say I want to generate a table where the chains are 100 000 hash/plaintext long. I ...
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102 views

Does adding more characters to the Enigma rotors improve crypto strength?

This seems like an obvious question but I haven't been able to find it, so here goes: Enigma is based on an alphabet of A-Z (26 characters); obviously this directly affects message content (e.g. ...
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In NTRU, if $N$ is not prime, prove that one can recover the private key by solving a lattice problem in dimension lower than $2N$

In the NTRU cryptosystem, it is suggested to take $N$ prime. I want to understand why. In Jeffrey Hoffstein, Jill Pipher and H. Silverman An Introduction to Mathematical Cryptography, they suggest (...
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622 views

What are some good examples of modifying crypto where flaws are not really obvious? [closed]

I run into some developers from time to time who sometimes try to modify crypto which I end up saying along the lines of "Don't modify crypto." Usually, the question I get is - "OK, tell me why is ...
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27 views

Does Kasisky test for Vigenère cyphers assumption always hold?

In the notes from which I'm studying I read about Kasisky test: "Key observation: Two identical segments of $l ≤ L$ plaintext letters, will be encrypted to the same $l ≤ L$ ciphertext letters." ...
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51 views

Is there a problem in a PK cryptosystem if the plaintexts are very small compared to the ciphertexts?

I'm wondering, suppose we have a public key cryptosystem $P = (pk,sk)$ such that $$pk: \{0,1\}^n \to \{0,1\}^{n^2},$$ that is, the ciphertexts are $n$ times longer than the plaintexts (here, $n$ is ...
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202 views

What is the point of differential cryptanalysis when the amount of necessary plaintext is unrealistic?

As someone with a non-crypto background, I learned that differential cryptanalysis is mostly weak against ciphers like DES because, being a chosen plaintext attack, for a state of art complexity of $2^...
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481 views

How to deal with a cipher with addition and XORs combined together?

I am trying to cryptanalyze a cipher where bitwise XOR and addition mod $2^n$ are combined together. I've been working on it for a long time but with no result - the main difficulty, which I am unable ...
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46 views

A5/2: Ciphertext Only Attack

A5/2 could be attacked with cipher-text only, using the Error Correction Code, in order to retrieve the session key. For the purpose of simplicity suppose that the error correction code copy the ...
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148 views

Any benefit to writing a message as a mix of 2 languages before encryption?

For example, imagine a message that is a mix of Japanese and English words; Japanese in unicode, English in ASCII. Japanese doesn't use spaces between words. The sentence structures, anything ...
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44 views

Found weil pairing. Index Calculus method on the results of weil pairing

Consider Elliptic curve with p = 59, A = 1, B= 0, P = (25,30) and Q=(35,31). So I tried to solve this using MOV attack. The torsion point for them E[5] is R(-25,30i) where is sqroot -1 Chosen two ...
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60 views

Are analog quantum computers a threat to RSA and DLP?

We already know that D-WAVE's "quantum computers" can't really run the Shor's algorithm, because the way they're built doesn't qualify them as universal quantum computers. Now researchers actually ...
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27 views

Error Detection/Correction Code-Then-Encrypt

I've just studied about the error correction schemes and encryption. First rule when using EDC/ECC is to first encrypt and then calculate them, and the major motivation we were told is that "EDC/ECC ...
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101 views

Reversing a known encryption algorithm (4-byte repeating key XOR)

I've been practicing for an upcoming CTF competition, and I've finally reached the cryptography stage. I'm a complete newbie in this field (my knowledge is essentially that bcrypt is awesome and md5 ...
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1answer
36 views

How can I determine key length for message encrypted by many-time-pad?

For message $ m $ and key $ k $ I get encrypted message $ c $ ($ m \oplus k = c $) where $ length(k) < length(m) $. Additionally I know that message $ m $ is English text. Instead of using pure ...
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Countering Cryptographic Attacks

By reading Camellia Design and Analysis document following is my understanding about few cryptographic attacks from designer point of view. Differential and Linear Crypt-analysis. Number of Active ...
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Concept of “guessed ID” in Authenticated Identity-Based Encryption

In Authenticated Identity-Based Encryption by Ben Lynn, in Proof of Integrity (section 4.3) and Proof of Security (section 4.4), I cannot grab the concept of "guessed ID" . Because encryption differs ...
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60 views

Plotting Running Times of SAT solver

In the the paper "Efficient Methods for Conversion and Solution of Sparse Systems of Low-Degree Multivariate Polynomials over GF(2) via SAT-Solvers" there is a Figure that I can not understand and I ...
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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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Are transposition ciphers insecure?

Given plaintext: P[i], i = 1..N Given stream of cryptographic numbers S[i, j], i = 1..N, S[i, j] in [1, j] generated by RC5 for example We encrypt using Fisher-Yates shuffle algorithm: ...
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Is this a better involution S-Box for the Anubis cipher?

After swapping random indexes of trivial involution $S[x] = ¬x$, I found the following involution S-Box with a non-linearity of $98$ and a differential uniformity of $6$. Is there an upper limit to ...
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63 views

Factorization of RSA modulus using a qubic residue

Suppose that someone uses RSA with $n = pq$, exponent $3$, also $3$ divides $\varphi(n) = (p-1)(q-1)$ and $2$ different roots $y$ and $z$ of the equation: $$x \equiv c \ (mod \ n)$$ are known (for ...
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40 views

Security Strength of Double Substitution Ciphers

I am wondering why people are using RSA keys when some types of double substitution ciphers seem to be just as secure if not better off. By some types of double substitution ciphers I mean one Which ...
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61 views

Why is it that most messages seem to be expanded?

Whenever I have seen a more secure version of a message, the message seems to be expanded by some factor. One example is RSA encryption, but whenever a message does not appear to be expanded it is ...
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127 views

Example of Software Security (White Box Cryptography) is not strong as Hardware Security?

I have been reading about White Box Cryptography in the last 2-3 days but I was wondering what are the example of White Box Cryptograhy that are quickly broken by Cracker / Hacker? Would the fact ...
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On a proposition in NTRU original paper: $\gamma_1 |f|_2 |g|_2 \leq |f \circledast g|_\infty \leq \gamma_2 |f|_2 |g|_2$

In the original paper of NTRU cryptosystem, we have the following proposition (that is said to be suggested by Don Coppersmith): For any $\epsilon > 0$, there are constants $\gamma_1,\gamma_2 &...
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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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57 views

How to brute force sqlcipher encrypted file with MD5 hash of a 7 bit key?

I have a database file that is encrypted using sqlcipher and MD5 hash. Sqlcipher to my understanding provides 256 bit AES encryption. The key is 7 bits long. How do I brute force it?
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Not-So-Simple Substitution Cipher?

The first go-to weakness when talking about substitution ciphers is frequency analysis. It assumes that there's a simple 1 to 1 character mapping between the plain text and the cipher text. Could a ...
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Is this approach able to protect against padding oracle attacks?

I know that a protection against the padding oracle attack is to encrypt-then-mac. This is to avoid trying to decrypt a modified ciphertext, and leak information about padding errors. Suppose that we ...
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35 views

RC4 using a key without nonce's or IV's [duplicate]

I'm researching RC4 and I am trying to recreate a condition where RC4 is crackable. However I can't quite find the article/resource I need to find the weakness for an implementation like this (python):...
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81 views

How to find the keyword of the Playfair text knowing/not knowing the plaintext and having decrypted text?

I know how the Playfair cipher works. I would like to know how can I find the keyword of the play fair cipher in two cases: 1) knowing the plaintext 2) not knowing the plaintext? Some examples: <...
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94 views

Derive $x$ when given $g,g^x$ and $g^{(1/x)}$?

If an adversary has access to the generator g of a group G and is given access to $g^{x}$ and $g^{(1/x)}$, will it make it any easier to derive the value of $x$ compared to when he had access to only $...
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102 views

Correlation Immunity Of 4 bit S Box

I have a 4 bit S Box byte[] S = new byte[16] { 0x9, 0xE, 0x5, 0x6, 0xA, 0x2, 0x3, 0xC, 0xF, 0x0, 0x4, 0xD, 0x7, 0xB, 0x1, 0x8 }; How can i calculate Correlation ...
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How to break a 32 bit block cipher without key?

From what I know Skip32 is the only 32 bit block cipher and I heard its not secure. What do I do or which tool do I use to break a 32-bit block cipher? I did search for this but all I find is attacks ...
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148 views

differential cryptanalysis cipher for the final round

I have a problem to find the sub-key. The system is… For each round, we make the following stage: We add the round key $K_i$. Substitution : we have 8 blocks of 4 bits, and an S-box ...
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81 views

Cryptanalysis of XOR cipher with repeated key phrase

My assignment is to cryptanalyze cipher text that we know was encrypted with a stream cipher (bitwise XOR of plain text and key stream), and decrypt to plain text. We know the key stream is a repeated ...
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How is the block size of a block cipher related to how susceptible the block cipher is to a birthday attack?

For example what can you say about how susceptible Triple-DES is to a birthday attack due to the fact that it has a block size of 64-bits.
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How to break a Quagmire 3 cipher?

What would be a good way to go about attacking a Quagmire 3 cipher? I understand that it is polyalphabetic with a key and an indicator. I have started by taking the cipher text, taking every n-th ...
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Is this PRG secure?

$G$ is a safe PRG in range $\{0,1\}^n\rightarrow\{0,1\}^{n+1}$. Let us define $G'(S)=G(S\oplus G(S)_{1,...,n})$, s.t. $G(S)_{1,...,n}$ is the first n bits of $G(S)$. Is $G'(S)$ a secure PRG? ...
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Conditions for a successful Differential Power Analysis attack

From this paper, there are two conditions for a successful DPA attack: i) there exists an intermediate variable in the implementation that is correlated with the power consumption and ii) ...
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119 views

How much weaker is AES-64 than AES-128?

It's hard to say exact QC specs, but let's assume we have decent a quantum computer using Grover's algorithm that is able to half AES-128 keyspace to that of AES-64. How long will a bruteforce attack ...
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225 views

Should HMAC-SHA3 be preferred over H(C(k,M))?

If I understand correctly SHA-3 (Keccak) is resistant against more attacks than SHA-2. This would make it possible - again if I understand correctly - to use SHA-3 with a simpler scheme than HMAC. ...
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541 views

Are there attacks on AES with 16-bit keys? [closed]

Are there known attacks on AES that uses a 16-bit key? Assuming the data can be 95MB size, and that I can request the same data over and over. For example, can someone explain to me how this code ...
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What kind of analysis can I perform on my implementation of Salsa20 and Rabbit ciphers?

I've implemented both the Salsa20 and Rabbit ciphers in C#. My implementation is for academic purposes and I've tested both of them against the test vectors. I implemented a system that encrypts a ...