# All Questions

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### Efficient way of generating a random number of N (less than 64) bits with exactly M bits equal to one

Would there be an efficient way to implement a function with the following signature: unsigned long long int random_word(size_t n, size_t m) that would generate ...
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### CCA security of this schema

Let $k$ be uniformly sampled from $\{0,1\}^\lambda$, $F$ be a secure PRP with block length $\lambda$ and let $Enc(k, m)$ be such that it returns $c = (F(k,r), r \oplus F(k,m))$ with $r$ uniformly ...
41 views

### Do Partially Homomorphic Encryption schemes also suffer from noise overflow?

Do PHE schemes in general also suffer from noise overflow problem?
148 views

### Randomness Testing of Cryptographic Algorithim

I am new to algorithim randomness and confused at I guess a basic level question. Is it common for any cryptographic algorithim to have repetitions in its output i.e.let say 34 and D8 are two ...
108 views

### How can we effectively compute the sqrt of some element in the group?

I only know one way, if this group is a cyclic group, and we know the element can be expressed in $g^m$, then $g^{(m/2)}$ is the answer. Another question, if $m$ is an odd number, can we be sure ...
12 views

### Decode/decrypt Cipher text of unknown custom algorithm [on hold]

I have a university assignment by the professor to decode unknown encoding schemes but i haven't able to decode. The message is sample of communication between Indian external affairs to different ...
17 views

### Does BLS aggregating signatures allow duplicate signatures?

If there is a message $m_1$ that $H(m_1) \rightarrow g^r$ and there is another message $m_2$ that $H(m_2) \rightarrow g^k$, where $g^k$ is also a generator of $G$, is this possible? then $g^r$ could ...
54 views

### Statistical Analysis of Cryptographic Hashing Algorithms

I was wondering how can I use NIST Statistical Test Suite to check for the randomness of output generated by a cryptographic hashing algorithm, let say SHA-256? To be specific, how will I generate ...
22 views

### 1-out-of-2 Oblivious Transfer Security

Just started reading Oblivious Transfer. I am searching for a proof of security based on RSA implementation but I can't find anything simple to understand. Can someone direct/show me to an easy to ...
44 views

### Pollard's $(p - 1)$ factorization method runtime

Wondering if anyone knows a good reference for Pollard's $p-1$ algorithm's runtime? I was looking on the Wikipedia page and the runtime cited there is $\mathcal{O}(B\cdot \log B\cdot \log^2 n)$. ...
56 views

### How are Data Science and Cryptography related?

Is there any interesting connections between Data Science And Cryptography. Data Science involves using Statistical Analysis to analyze data while Cryptography also involves Statistics in ...
33 views

### How does the challenger choose the message randomly in the one-wayness game of PKE?

I have read some papers that give the definition of one-wayness of PKE schemes. Let $\Pi = (G,E,D)$ be a PKE scheme, and the security game of OW-CPA is defined as follow: \mathrm{Adv}_{\Pi,\...
48 views

### Nonce-misuse-resistance scheme applied after the fact to AES-GCM for defense in depth?

This is a follow-up to a previous question about encrypting IV/MAC results from AEAD ciphers. I have a system I'm working on that needs to use standard (NIST/FIPS) cryptography, at least for its ...
22 views

### Classification of BFV and CKKS scheme?

I would just like to ask what is the classification of both BFV and CKKS scheme are they Somewhat Homomorphic or Fully Homomorphic? Brakerski/Fan-Vercauteren (BFV) [Brakerski12, FV12, BEHZ16, HPS18] ...
99 views

### Use a SHA256 as a key for AES256

Is it safe to use the SHA256 of a hard-to-bruteforce string as the key to encrypt data with AES256?
100 views

### Is it safe to reuse the password when using AES-CTR with scrypt?

I want to encrypt several files with the scrypt encryption utility. Here is an overview of its file format, which gives an indication of what it does: ...
29 views

### In using Boolean Circuits model of Computation in Homomorphic Encryption why is is considered fast?

I am currently doing some reading on Homomorphic Encryption for research purposes and based on my reading using the Boolean Circuit Model of Computation specifically in regards to Fast Fully ...
6 views

### CP-ABE implementation in cpabe toolkit

I have designed a CP-ABE scheme which is different from original scheme by bethencourt. Now the cp-abe toolkit supports the original scheme and in order to use the toolkit for my scheme I have to ...
38 views

### Finding and matching SHA512 Unsalted Hash

We are given a list of possible strings, there are $32^{16}$ ($=2^{80}$) to be exact. We also have the unsalted SHA512 of the original target string. How long would it take to go through those ...
30 views

### What does (06) in “CRL Signing (06)” mean?

In "Certificate details -> key usage -> CRL Signing (06)", what does "(06)" in "CRL Signing (06)" mean?
52 views

### Is it possible to construct a hash-based public key encryption scheme?

I know hashes can be used to construct symmetric encryption schemes (HMAC running in counter mode), signature schemes (SPHINCS), pseudorandom generators, etc. One thing that's missing is public key ...
332 views

### Algorithm to find primes $q$ and $p$ with $q\, |\, p - 1$?

I understand that if $p$ is prime then $p-1$ must be composite (at least divisible by $2$ as it is even). But how does an algorithm find a prime $q$ such that $q \cdot r = p - 1$. I thought prime ...
24 views

### why is index “a non-negative integer less than $2^{64}$” in the KDF for UMACs?

https://tools.ietf.org/html/rfc4418#section-3.2.1 describes the parameters for KDF as follows: ...
33 views

### Hey, anyone know if this is a color cryptography? If yes what? [on hold]

Me and a group of friends are solving an ARG, we found some videos where every frame was an image like this one.
35 views

### Are there any symmetric Partial Homomorphic Encryption Schemes?

Note that I am asking specifically for Partial Homomorphic Encryption (PHE) schemes and not Somewhat Homomorphic Encryption (SME) schemes. I believe there are several SHE schemes that are symmetric ...
76 views

### RSA, factoring with middle known bits of one prime?

It was shown by Coppersmith, that we can factor the RSA modulus with half of the most significant bits of one of the primes. And for the lsb case, assume that we known $p_0,k$, and $p=p_12^k+p_0$. ...
32 views

### Decrypting a weak PRNG Mersenne Twister Stream Cipher

I am currently working on the crypto-challenges presented here. I created a simple stream cipher using a Mersenne Twister RNG. It basically works as follows: Seed a RNG with the key (basically up to ...
32 views

### Generating anomalous elliptic curves with given order [on hold]

First of all please see this paper, I want to fully understand the section 3 and 4 of this paper and write a script that generates an anomalous elliptic curve with given prime order. Furthermore how I ...
40 views

### General factoring and one-way functions

Let a function $f$ be one-way, if there exists a probabilistic polynomial time algorithm to find the preimage of $y = f(x)$ for uniformly chosen $x$ with non-negligible probability. Define the ...
338 views

### What security risks does exposing the size of the plaintext entail?

For this question my focus is exclusively on symmetric block ciphers (with a particular interest in AES256 in CBC mode). I have read much discussion on various ways to pad the plaintext so that the ...
5k views

### How do I detect a failed AES-256 decryption programmatically?

I have implemented a simple encryption/decryption program based on AES-256 in CBC mode1. Actually, it is more precise to describe it as a compression+encryption / decryption+decompression program. ...
31 views

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### How to compute the number of instructions in python [on hold]

Could you please tell me how I can compute the number of instructions of a program written in python. thanks
63 views

### How do discrete logarithm with modulo a prime and a non-prime compare?

Let $c_N = g^i \mod N$ and $N=p \cdot q$ and $c_P = f^j \mod P$ and $P$ a prime We assume $N,P$ has the same bit-length. $P$ is the best type of prime you can choose (e.g. safe prime). $N$ is a ...
38 views

### What is / How would I calculate the number of bits(?) I need to make the probability of a collision very small?

If I wanted to create a TOTP-esque algorithm that generated a string n characters long, with each character being a base64 character, generated from a user secret <...