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votes
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13 views

How to break homophonic encryption

What is the best and most efficient algorithm to attack homophonic coding encryption?
-1
votes
0answers
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 ...
0
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0answers
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 ...
0
votes
1answer
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 ...
0
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0answers
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 ...
0
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1answer
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 ...
-2
votes
0answers
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 ...
0
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0answers
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....
0
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0answers
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: ...
1
vote
2answers
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 ...
1
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0answers
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 ...
1
vote
1answer
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.
0
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0answers
19 views

CBC-MAC padded message difference

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 ...
1
vote
1answer
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_{...
0
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0answers
10 views

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; ...
1
vote
1answer
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 ...
0
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0answers
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: ...
3
votes
3answers
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". ...
1
vote
1answer
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 ...
-1
votes
0answers
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....
0
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0answers
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 ...
0
votes
1answer
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 ...
0
votes
1answer
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 ...
0
votes
1answer
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 ...
-2
votes
0answers
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 ...
2
votes
1answer
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 ...
0
votes
2answers
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 ...
-1
votes
0answers
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 ...
0
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0answers
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: ...
2
votes
1answer
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 ...
-2
votes
0answers
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 ...
1
vote
1answer
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.
1
vote
0answers
31 views

RSA congruence (n is not given) [on hold]

it might be a silly question but i need help please given RSA system , where $n=pq , p\ and \ q \ are \ primes $ , $ v_0,v_1,v_2, v_3 \ are \ known $ $p^p \equiv v_0 \mod q$ $q^q \equiv v_1 ...
0
votes
0answers
20 views
2
votes
1answer
49 views

Why are PAKE protocols not widely used?

While there are plenty of PAKE protocols, especially those augmented ones which are practical in C/S model, actually they seem to be not widely used. Even TLS-Standardized SRP, the most popular one ...
0
votes
0answers
27 views

In DES : Matsui's notation(LC) vs Biham's notation(DC)

I'm doing linear attack for 8 rounds DES. And I just wondering about the difference between matsui's notation and Biham's notation. In Matsui's paper, numbers bits from 0 to 63 from right to left. In ...
2
votes
3answers
74 views

Why is “key-rotation” called key-rotation?

The word "rotate" in respect to "key-rotation" has connotations of looping/repeating variable values like a rotor, but as far as I can tell there isn't a single definition available for "key-rotation" ...
18
votes
1answer
4k views

How does IBM's 53-bit quantum computer compare to classical ones for cryptanalytic tasks?

IBM just announced "a new 53-qubit quantum computer". How does it compare to classical computers, performance-wise, for cryptanalytic tasks? E.g. finding a 48- or 64-bit value whose SHA-256 has a ...
0
votes
0answers
41 views

Calculating Maximum Index of Coincidence

I'm trying to understand how the maximum Index of Coincidence (IC) is found. This is the only description I have for it: "For a given period $P$ you can divide a cipher into $P$ groups, calculate the ...
0
votes
0answers
42 views

How can I understand this notation of a hash function from Classic Mceliece

I have no idea what does it mean $H(1, v, C)$, where $v$ and $C$. I know and how I can implement it in Sage. It's from Classic McEliece. Can anyone help me? Some example to check
0
votes
0answers
6 views

can I generate a fixed encrypted message of 16 values in Python [migrated]

I am using Python to create an RSA encoding system but I have to follow some conditions: Both of private and public keys have to be encoded in 16 values. The keys has to be encoded in 64 bits. I ...
0
votes
0answers
17 views

Saving Thales keys to different location than KMDATA/local

I'm generating cryptographic keys using Thales HSMs. The encrypted keys are stored to /opt/nfast/kmdata/local. Since I may need to generate a very important number ...
0
votes
1answer
24 views

Definition of support in the context of an encryption scheme and usage of P = NP assumption in lemma 9.2 (Arora, Barak)

EDIT: I've migrated the question by deleting the same question I asked on mathematics stackexchange. 2 questions: (1) I am confused about the definition of support used in the proof given in the ...
0
votes
0answers
81 views

Preimage attack on cbc-mac with constant key

Is a hash function created by using CBC-MAC with one public key that does not change secure against preimage attacks? If not, how could you exploit this to find a single block message that hashes to a ...
2
votes
1answer
67 views

zk-SNARKs vs. Zk-STARKs vs. Bulletproofs: definitions

I have become quite familiar with Bulletproofs the last few months. Bulletproofs is the name given to a zero-knowledge proof system for arithmetic circuits, by Benedikt Bünz et al. It is a specific ...
1
vote
0answers
109 views

CBC-MAC Padding weaknesses

I'm trying to wrap my head around how different padding methods affect the strength of CBC-MAC's. Suppose a message is split into different blocks, m1, m2, m3 etc. and the last block is padded with 0'...
2
votes
0answers
39 views

Compute ln function of a Paillier encrypted value

If I have an encrypted value $Enc(x)$ with Paillier cryptosystem, is it feasible to compute an encryption form of $\ln(x)$ or its approximation using homomorphic properties? The input $x$ is always ...
2
votes
1answer
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 ...
0
votes
2answers
61 views

HMAC for round-trip validation

I have a need to produce URLs to allow the downloading of a single file, without authentication. These links will be sent through email, and I understand and accept the risk of a given link being ...
0
votes
0answers
3 views

Can openssl's S/MIME handle RSASSA-PSS [migrated]

I need to sign emails with S/MIME and want to do this using openssl. The requested signature algorithm is RSASSA-PSS. I couldn't figure out how to specify the ...

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