# Tagged Questions

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”).

17 views

### A5/2 Ciphertext Only Attack

I've studied that A5/2 could be attacked with cipher-text only, using the Error Correction Code, in order to retrieve the session key. Here's an article I tried to read about it (section 4). (however ...
136 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 ...
36 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 ...
58 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 ...
20 views

### How do we compare two hash functions / cryptographic functions [closed]

I know what hash functions are but as my research project I am comparing two cryptographic algorithms so I am a bit confused about on what bases should I compare the two algorithms as these are ...
26 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 ...
119 views

### Using e-ID Number for Encryption and Digital Signing

I want to use e-ID number for performing Encryption/Decryption and Digital Signing - and in order to do so, I've opted a PGP-oriented approach which goes a bit like this. Generating PGP key-pair ...
82 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 ...
33 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 ...
59 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 ...
207 views

### Mathematical formula for switching the key for OTP?

Instead of generating the random key for the one time pad cipher over and over again, is there a mathematical formula that allows you to switch the key to a new key? The new key must be as random and ...
30 views

### Has this forum been compromised by the NSA BULLRUN programme? [migrated]

Today, this site shows 24 thousand users in Cryptography. It runs in parallel with and is associated with StackOverflow boasting 6 million users. This site then clearly creates some leverage and ...
38 views

### 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 ...
38 views

### 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 ...
79 views

### Does a key derivation function always generate an even distribution of bits in the resulting key?

I am a student of crypto. During our study course, we went into the AES-128 algorithm. All the examples given used an initial key k, 128 bits and we only briefly touched on the key derivation of ...
202 views

### Hypothetical encryption technique, is it secure?

This to me, sounds like a great idea, but with all rosy-tinted ideas it needs some grounding in reality. Here are the steps of the hypothetical system (with the hypothetical part highlighted): User ...
18 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?
106 views

### Ciphertext with uneven letter distribution

I have a ciphertext encrypted with an unknown method. It is part of a challenge (personal quest), so I can not post it. The letter statistics is the following: ...
111 views

### Calculation of the avalanche effect coefficient

Given a strict avalanche criterion matrix/dependence matrix for a hash function,how do I calculate the avalanche coefficient for it. I want to calculate a single parameter(value) which represents the ...
8k views

### Now that quantum computers have been out for a while, has RSA been cracked?

D-wave systems has released a commercially viable quantum computer. This means in theory, that all asymmetric encryption algorithms — such as RSA — are now useless due to the speed at which quantum ...
57 views

### 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: ...
47 views

### 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 ...
7k views

### Security strength of RSA in relation with the modulus size

NIST SP 800-57 §5.6.1 p.62–64 specifies a correspondence between RSA modulus size $n$ and expected security strength $s$ in bits: ...
105 views

### K Friedman - two texts explanation

I read the $K$-Friedman test to determine the period of a Vigenère ciphertext, and I understand something like this: $K$-Friedman test tries to find out what period of the cipher by calculating some ...
33 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: <...
62 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 ...
88 views

### 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 ...
1k views

### How does cryptanalysis of the Playfair cipher work?

I have a set of Playfair-enciphered data that I'm trying to crack without the key. I know I need to analyse bigrams; I've currently worked out what decrypts to th, <...
60 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 ...
34 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 ...
328 views

### Perfectly secure shift cipher

Prove that if only one character is encrypted using a shift cipher, then the shift cipher is perfectly secure. I want to show that $P(P=p | C=c)=P(P=p)$. But I don't know how to relate. Can anyone ...
47 views

106 views

### Comparison Vigènere vs. Monoalphabetic cipher

I have a question for a class of secure communication, but I have no idea about how to proceed in order to answer it. I'll be very grateful to whom replies to me. Assuming that brute force attack ...
39 views

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: ...
48 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?
35 views

### 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 ...
869 views

### Using Chi-Square for Vigenère Cipher

I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenère cipher. I came across a website that describes the Chi-Square statistics in a ...
38k views

Suppose Alice wants to send encryptions (under a one-time pad) of $m_1$ and $m_2$ to Bob over a public channel. Alice and Bob have a shared key $k$; however, both messages are the same length as the ...
222 views

### How are constructs with data-dependent swaps and rotations cryptanalyzed?

Linear and differential cryptanalysis seem well suited for constructs with a (relatively) simple fixed structure of boolean expressions. But some ciphers incorporate swaps of array elements where the ...
909 views

### What is the smallest plaintext/ciphertext size for an algorithm like?

When I read about a choosen plaintext attack, for example on AES the block size is always 128 bits, does it mean the attacker will only supply 128 bits data words as "plain text" ?
1k views

### Security of N bit HMAC

Lets say that I am using 128 bit HMAC. How many operations are needed to find a "non secure" message. Is a birthday attack possible?
479 views

### Is there an algorithm to find the number of intersections of two sets?

Suppose both I and my friend have a set of integer numbers. We want to know the number of common elements in our two sets but without knowing elements of the sets of each other. So I don't want my ...
64 views

### 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 ...
34 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):...
### 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 \$...