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# 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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196 views

### How to solve this Baby Bleichenbacher Attack?

I am trying to solve this problem from https://toc.cryptobook.us/book.pdf. I am having trouble with this question : (Baby Bleichenbacher attack). Consider an RSA public key (n, e), where n is an RSA ...
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### How do I know the most efficient image encryption algorithm?

I am familiar with any algorithm that is based on the number of bits in a key (n-bit) and how to restore a key, such as the Discrete Logarithm Problem or Factorization.  When I use any algorithm for ...
544 views

### A probable attack for RSA (factorization): how to improve it?

A probable attack for RSA (factorization): how to improve it? $N=8*G+3$ can be factored if there is a non-trivial negative $k$ such that $\frac{(N*(9+24*k)-3)}{8}=-6*m^2$ [to exclude the two trivial ...
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### Is it safe to initialize a random number generator with MD5?

The MD5 algorithm is no longer considered secure for most applications of a hash algorithm. However, is it safe to initialize a PRNG via a password? If it is not, how could it be exploited?
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### What kind of special numbers are not suitable as RSA keys?

I have read that some integers are not appropriate to be chosen as the modulus in an RSA cryptosystem. Some of these numbers are those that, given a modulus $n=pq$, then $p-1$ or $q-1$ do not have ...
38 views

### How to compute $x_0$ in Chaotic Logistic map in special method?

I know that the Chaotic Logistic map is $x_{n+1}=Rx_n(1−x_n)$. I read some articles about the Chaotic Logistic Map, but some things are not clear. Someone wrote in his article the following: The ...
88 views

### Is Index Calculus Attack on hyperelliptic curves feasible with a common laptop?

I am studying this paper about an index calculus attack in hyperelliptic curves for genus $3, 4, 5, \dots, 9$. Nicolas Thériault, Index calculus attack for hyperelliptic curves of small genus, 2003. ...
1 vote
53 views

### Using multiple asymmetric keys as backups for one another

I've been thinking about ways to take advantage of multiple asymmetric encryption schemes so that each key could be a backup to the others in case of cryptanalysis of one given scheme. Those public ...
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### Is there a way of mitigating weak states in the Spritz stream cipher algorithm?

The Spritz stream cipher algorithm has been shown to have a special class of states that can be used to do a full state recovery attack better than brute force. While the authors of the paper clearly ...
81 views

### Textbook RSA with $e=3$ and short random message

This is a simplified version of a question I made long ago, that never got an accepted answer. It's given $N$ of $n=2048$ bit, assumed hard to factor, which two prime factors each are $\equiv2\pmod3$, ...
250 views

### Breaking RSA with P,Q LSB bits

Let's say we have a certain amount of LSB bits of P and Q and we want to fully reconstruct them given N=P*Q. I know this problem was studied in literature by Coppersmith and that Lattice methods are ...
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### Provably secure and Practical ciphers

Are there any ciphers that are provably secure (reducable to a hard problem (including like factorization, not necessarily to NP-Complete or harder) ) are practical (not necessarily for too much ...
72 views

### Recovering original bit vectors that constituted XORed binary vectors

I am trying to unscramble received data packets. Each packet is divided into 3 parts ($A$, $B$ and $D$) with equal lengths. In every packet, each of these parts are scrambled/encrypted with an unknown ...
1 vote
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### What does $(a+b) \bmod{256}$ and $a$ XOR $b$ reveal about $a, b$?

Say $a$ and $b$ are some uniform random $8$ bits so that the entropy of $a$ and $b$ is 8 bits each. If I show you $(a+b) \bmod{256}$ and $a$ XOR $b$, then what can you tell about $a$ and $b$? Or how ...
110 views

### predict random keys using python [closed]

How can I write a program in python to predict the random key (urandom) that is used for encryption? I tried to search and I couldn’t find anything related to guessing and predicting urandom in python
109 views

I was playing a game on cryptography where I encountered this problem: Hashed Value of password: 24 109 76 35 22 94 83 25 106 104 73 87 56 38 56 50 10 92 58 84 44 88 24 112 125 121 125 43 122 55 106 ...
288 views

### Which is the smallest, cyclic in 3 directions, consistent structure of random values which can be hidden at the adversaries machine? (some comparison)

Or more general each member can be part of up to three 2D locally euclidean planes of 2 different dimensions each. (each of those planes is cyclic in two orthogonal directions, like a torus) Given ...
1 vote
57 views

### Can I decrypt AES-CBC ciphertext if I have the key without IV? [duplicate]

Can I decrypt ciphertext from AES-CBC encryption, if I have the key and ciphertext only?
195 views

### What is the effect of low rank dual sublattices on the dual lattice attack on LWE?

In the dual lattice attack of Espitau, Joux and Kharchenko (On a dual/hybrid approach to small secret LWE), the authors propose distinguishing (and subsequently recovering secret values) of LWE ...
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### Computational indistinguishability of two LWE type samples

Consider the problem of distinguishing between polynomially many samples of either \begin{equation} (x, b, As + e) ~~\text{or}~~\left(x, b, ~Ax + b\cdot(As + e) + e'\right). \end{equation} Here, $A$ ...
1 vote
61 views

### On the effectiveness of Sidelnikov-Shestakov attack under a bad guess

I have been studying Wieschebrink paper "Cryptanalysis of the Niederreiter Public Key Scheme Based on GRS Codes". In the paper a cryptosystem using GRS codes is exhibited with an attack ...
1 vote
139 views

### Why does differential cryptanalysis always start from the last round?

Suppose we are working with a cipher with the same general structure as AES. I want to attack the cipher in the following way: suppose that the differential holds only for the first round (much higher ...
65 views

### Enumerating values from a linear congruential generator java Random()

During my research on a java application, I discovered that the nextInt(64) function of the java.Random() class is used to ...
78 views

### Indistinguishability proof of an encryption scheme

Is there any indistinguishability proof (e.g., IND-CPA, IND-CCA, IND-CCA1, IND-CCA2, IND-CKA) based on games that involve breaking the AES security? Usually the proof involve breaking hard problems ...
181 views

### Shift cypher, perfectly secure?

I know that if only one character is encrypted using a shift cipher, then the shift cipher is perfectly secure. But what if the space of keys is greater than the space of messages? Would it still be ...
75 views

### limiting number of queries to Enc. or Dec

Why do we limit the number of queries to Encryption or Decryption oracles in the security analysis of various encryption schemes to be polynomial in the security parameter n?
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### Does the searchable encryption scheme satisfy trapdoor indistinguishability?

In a searchable encryption scheme based on the certificateless cryptosystem, the trapdoor generation algorithm only has a hash function that outputs an integer value. Does the scheme satisfy trapdoor ...
106 views

### RSA rsa residue class ring

I've been working on the RSA method for several weeks and I don't understand what this residual class ring is all about. I understand that if $x^e \bmod n$ there must be $x<n$ because of ...
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### What would be the benefits of a fast PRNG that produces an 8-bit output and could pass 1 Peta Byte of the PractRand test?

Assuming that all other elements like the internal state of the algorithm are considered secured and very hard to discover from a cryptanalytic standpoint. How significant would be for the algorithm ...
121 views

### Difference between WhatsApp and Signal implementation of the Open Whisper Protocol

WhatsApp has taken the step of using the Open Whisper Protocol for their message encryption, borrowed from the Signal application. I was wondering if there was any obvious, high level, difference in ...