# All Questions

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13 views

### How to break homophonic encryption

What is the best and most efficient algorithm to attack homophonic coding encryption?
10 views

### How does this frequency matrix for the english language work?

I was reading a PDF (here) about using heuristic algorithms to break homophonic encryption, and came accross a graph generated with digram frequency analysis (section 2.2, table 1). Reading the ...
17 views

### Is F_k_1(x) \xor F_k_2(x) a pseudorandom function?

I'm trying to determine if $F_{k_1, k_2}(x) = F_{k_1}(x) \oplus F_{k_2}(x)$ ($k_1 \neq k_2$ because that would be lame) is a pseudorandom function. My hunch is that it is. My reduction proof proceeds ...
17 views

### Optimising shor's algorithm

So I've run into this challenge where I was given the guess $g$, and the power $p$ of Shor's algorithm. All I have to do now is $g^{p/2} - 1$ and then GCD the result with n. But the problem is ...
29 views

### Key derivation for AES-GCM using HKDF?

I have a system comprising N >1000 nodes. At each node I would like to use HKDF to derive a unique 256-bit key, Kn (for the nth node), from a pre-shared master key, K0, and a locally-generated random ...
24 views

### How does gpg know what cipher algorithm is needed for decryption?

I am using gpg to make encrypt a tar.gz. My first try uses --verbose --symmetric and then the decryption is done with ...
26 views

### Encrypt letters to numbers using ASCII value. Using Mod 23 not 26!

Design a program that can convert a given string to an encrypted form as well as an encrypted sequence to a string using char* Convert letters to numbers. The letter is encrypted through it's ASCII ...
18 views

### Decrypting a TripleDES with encoding/Ciphers

I would appreciate some help, I've been given a set of encryption Keys, vectors. My coworkers and I are tasked with decrypting the string in order to produce specialized requests to an outside service....
11 views

### Why does mbedtls_rsa_rsaes_pkcs1_v15_encrypt() to make wrong encryption? [migrated]

I use mbedtls library for my small crypto application. mbedtls API has this function: ...
22 views

### Most efficient way to crack a monoalphabetic substitution cipher with spacing intact

I've got a cipher I've been challenged to crack by hand. It's a monoalphabetic substitution cipher, and the English spacing is intact, so all of the words are the right size. Is there a more ...
24 views

### Are biases narrowed towards the provenance of hard NP complete problems relevant?

I hear of randomized reduction, deterministic reduction and non-deterministic reduction of complexity from A to B problems. This could make things impossible for polynomial time adversary prying into ...
25 views

### XCBC Authentication

So XCBC was made to counteract lengths attacks against CBC-MAC, but how exactly does the modification made defeat this attack? All I can find are a few papers on why 2-key XCBC isn't actually secure.
19 views

If an attacker had a padded message and its corresponding CBC-MAC tag, how would they construct another message which produces the same tag for the same key as the original? The padding scheme used in ...
35 views

### Building Key Streams from PRNGs

I am reading an intro book about cryptography and the author tries to explain why using pseudo random number generators is vulnerable. Given PRNG equation; \begin{align} S_0 &= \text{seed}\\ S_{...
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### Building Key Streams from PRNGs [duplicate]

I am reading an intro book about cryptography and the author tries to explain why using pseudo random number generators is vulnerable. Given PRNG equation; ...
34 views

### Block cipher linearity (in relation to hill ciphers)

So while I knew hill ciphers were a form of block cipher (I'm assuming all the ones I have solved to date were ECB or something similar), so that got me thinking. Is it possible to use hill ciphers in ...
12 views

### Is it possible to sign a message with a base58 secret key with Tweetnacl library? [migrated]

I've generated a key pair using Tweetnacl.js: ...
61 views

### What's the likelihood of a collision if I use a hash to detect data change?

I have a set of data that I want to sync, and instead of sending an entire set of data, I wanted to use a hash. It is basically a list of GUIDs with either "true" or "false". ...
49 views

### How can we reduce indistinguishability-from-random to other security notions?

In probabilistic encryption schemes, different notions of security exists. I'm interested in the relationship between two notions. One is the indistinguishability-from-random notion of security and ...
24 views

### How Can I implement this hash function in python/Sagemath [on hold]

I don't know how Can I implement hash function H(1, v, c). I know values v, c. Cryptosystem: Classic Mceliece First screenshot https://arxiv.org/pdf/1907.12754.pdf Second screenshot https://classic....
16 views

### Do I need to use a matrix of size N x n for the public key in the BGV scheme when using Ring-LWE?

I'm going through the BGV paper and trying to make a toy implementation, but I just want to focus on Ring-LWE. In the paper, they set $N = \lceil{(2n + 1)\log_2(q)\rceil}$, and generate $A'$ uniformly ...
30 views

### Proving a function is or is not a pseudorandom function F_k(x) = F_k(x)||0

I have 4 functions to analyze. I need to determine if they are or are not pseudorandom and give a proof/counterexample. I'm having trouble just determining if they are - let alone proving or giving ...
21 views

### Constant number of rounds in Yao's Protocol for semi honest adversaries

According to me, every OT takes a constant number of rounds and since we have to do an OT for every input of one party, we'll have to do O(n) OTs which would correspond to O(n) rounds. But I have read ...
21 views

### Is CECPQ2 forward secure?

Is the CECPQ2 key exchange, as deployed by Google[1] and Cloudflare[2] in TLS 1.3 forward secure against quantum computers? I know that it is using HRSS+SKY as the post-quantum part of the key ...
37 views

### An assignment topic in cryptography [on hold]

I'm currently taking a course in cryptography. I'm supposed to make reference to a research paper related to cryptography and prepare a document as part of my course assignment. I request someone to ...
23 views

### Maintaining validity of ZKP throughout re-randomization of homomorphic ciphertext without linkability to previous ciphertext

Question: How is it possible to adapt a ZKP for a homomorphic ciphertext to still be valid after said ciphertext has been re-randomized? Context: In a lot of e-voting systems homomorphic encryption ...
40 views

### Differential privacy on medical data

When we apply the differential privacy on medical data to protect the personal data of the patients, how the doctors can access the original data to analyze them and to intervene in real-time. In ...
22 views

### How to build a bloom filter based on p-stable locality sensitive hashing functions? [on hold]

p-stable locality sensitive hashing function:$$h_{a,b}(v)=\lfloor{\frac{a\cdot v+b}{w}\rfloor}$$ a is a vector random choosed from normal distribution, a is uniformly choosed from $[0,w]$, v is a ...
47 views

### Find salt that produces hash(knownInput , salt) = knownOutput

Hope anyone can help! As title says, I need to find a unique salt that produces knownOutput, using knownInput, when calculated like this: ...
63 views

### Why can't AES-GCM be used in IKEv1 phase 1?

I was configuring a VPN on a firewall (fortigate) and realized that I could use AES-GCM for encryption in the IKEv1 phase 2 but not in the phase 1 and I was wondering why knowing that in IKEv2 we ...
31 views

### What is this hashing method called? [on hold]

I was searching around and experimenting with hashing algorithms by hand, and I found this algorithm: Input: Yo Then we convert it to Ascii Hexadecimal, so it's ...
69 views

### Is SHA256 resistant to second preimage attack?

I am looking into building a merkle tree algorithm and I need to know if SHA256 is resistant to second preimage attack.
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52 views

### Why BGW Multiplication Gate Works?

I am reading Pragmatic MPC (link) about the BGW protocol. I also cross-reference here (click on lecture link for slides) *The BGW Construction for the Information Theoretic Setting – Benny Pinkas I do ...