# All Questions

18,422 questions
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### Breaking the Geheimschreiber using known-plaintext attack

I'm taking an intro course to cryptology, and we have an assignment challenging us to break the Geheimschreiber, or G-Schreiber, using a known plaintext attack. The plaintext is the Latin alphabet ...
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### create a time capsule on wots

i was wondering if there's any option to create sort of a time capsule in a word Document, meaning not encrypted by password rather than a date- let's say i send the document today but the receiving ...
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### What is meaning of the term “language”?

I don't have much formal background but I could not find a suitable explanation for this after searching on Google/Wikipedia. What is the meaning of the term language as used in cryptographic ...
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### Authenticated encryption and file data integrity

I've got a task to provide the integrity and an authenticated encryption for files in our application. I need an assurance if my way of thinking is correct. I can't use AES GCM, I have to stay with ...
180 views

### Would DES be secure with 128 bit keys?

Assuming you only modify the key schedule so that each of a 128-bit key is used at least once, would DES be about as secure as other ciphers such as AES? I am not talking about 2DES/3DES or other ...
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### Cryptoanalysis using Frequency Analysis

Hy community, I have read some documents to decrypt ciphertext without key using Frequency analysis. here are my questions : If the most occurring Char is not 'E' then how do we start? Let's say I ...
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### What is the shortest ciphertext size output by FHE?

Assume we use batching and modulus switching techniques to reduce the size of ciphertext in fully homomorphic encryption (FHE). Question: What is the shortest ciphertext bit-size output by the most ...
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### Can neural cryptanalysis be applied to AES?

In this Wikipedia article about Neural cryptography (section applications) it states: In 1995, Sebastien Dourlens applied neural networks to cryptanalyze DES by allowing the networks to learn how ...
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### What is the common way to find the distance dual of linear block code?

I know the distance of dual of reed solomon codes is n-k+1 beacuase it is MDS code. Now us consider the following linear block code C:\mathbb{F}^{k}\rightarrow \mathbb{F}^{n}\\ (c_0,...
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### Two parties SPDZ Protocol Input sharing

Assume we have two computing parties for SPDZ protocol. The two parties are also the input parties. How can they share the MACs on their input shares assuming one party is the master who owns the MAC ...
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### Does Proxy re-encryption can re-encrypt large data?

Many resources talk about the benefit of Proxy Re-encryption (PRE) and I also implement my PRE using Elliptic Curve key pair. But after I set up Global parameters, I can encrypt very small data maybe ...
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### Steganography question about pixels [on hold]

You ae given the following phrase "Stop Now" and you have a 100x100 pixel image where each pixel is represented as an 8 bit gray-scale quantity. With these pixels below, show as much as you can hide ...
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### Is there any bias whatsoever in modern hash function outputs?

We know that the output bias of a randomness extractor is $\epsilon = 2^{-(sn-k)/2}$ from What is the relationship between entropy conditioning and final output bias in a TRNG?. The following is a ...
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### Factoring RSA weak modulus

Given a public key for RSA, I have extracted the modulus which looks like this : ...
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### What is a SHA1_Compress() function?

I'm trying to implement the scrypt key derivation function using JavaScript. When implementing the algorithm, I found that there was a function called SHA1_Compress listed in the specification. Is the ...
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### Signal protocol: when, and why, is X3DH run again between the same two users?

This question concerns the Signal protocol's X3DH key agreement protocol as documented here. Obviously, if Alice and Bob have never contacted each other before, they need to run X3DH at least once to ...
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### Can you encrypt a 256bit password with a 256bit key so that it cannot be bruteforced?

Lets say we have an arbitrary but dictionary attackable password that is less than 256bit. (Lets just say the password is '1234Password'). We encrypt this password with a securely random 256bit key ...
428 views

### Do PGP keys with expiration date set expiration date in Encrypted messages too?

So I am little confused about a type of encryption I read about. You can encrypt your E-mails and pretty much all kind of information using PGP key pairs. However, I am confused if an encrypted ...
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### How to compute hash value on cipher text using hash function? [on hold]

Please kindly help me, I would like to compute hash value on cipher text.
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### Is there a cryptographic approach to availability

Background Cryptography can be said to provide the tools used to fulfill the goals of information security. The three pillars of information security are confidentiality, integrity, and ...
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### AES-128 (CBC) brute force given 90+ rightmost bits of key, known IV and Ciphertext?

Given: Known ciphertext (in hex) (ciphertext is the exact length of the message (i.e. non-padded). It is known that the cipher was developed using CBC. There is one and only one ciphertext message ...
32 views

### Reduction function Generation

I think I know how rainbow table works , I just wanted to make basic reduction function(for md5) in python with an approach that I am not taking a certain portion of hash but am taking the full hash ...
184 views

### How difficult is it to guess a salt based on a hash and known plain text?

I have the following use case: Alice owns the domain alice.com and Bob owns bob.com. I want to users to create a hash for ...
91 views

### $\boxplus$- key addition vs $\oplus$- key addition

GOST cipher , Hight cipher and SEA cipher use key addition based on modular arithmetic addition (module key size $\boxplus$) compared to many ciphers which use arithmetic addition modulo 2 ( $\oplus$)....
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### Prime Generation density and Miller Rabin Testing

I am working on an Cryptographic exercice but I'm not quite sure where to start. We suppose a prime generation consisting over a loop to take a random integer n and pass its number to a 5 round ...
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### Looking to verify my understanding of RSA math

I want to explain RSA to a programming audience with no cryptography background and I want to be sure my explanation is correct. The goal is to help them understand how RSA works under the hood. You ...
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### A modification of the NMAC construction

Consider the NMAC construction: This is a proposed exercise in my notes: Assume F is a PRP with $n = l(n)$. Is it secure to replace $k_0$ by $F_{0^n}(k_0)$ and $k_i$ by $F_{0^n}(k_i)$? In ...
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### A key-generator outputs an encrypted string that only changes the second half - what weaknesses could that expose?

The company I work for provides a software solution. The software is licensed and I have access to the license generator (which, BTW rules me out as a cracker - I don't need to crack the license, I ...
48 views

### Encrypted Database

I'm trying to build a encrypted database where we cant trust on the database manager. And since encrypt data in a deterministic way is bad, attackers can recover information doing frequency attacks, I ...
336 views

### Hardware RNG Bias

I have generator based on sampled noise (reverse-biased transistor - actually ChaosKey but that's not that important). The noise source is fed into ADC and sampled with 16bit resolution (2 bytes). ...
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### Give a distinguisher to differentiate between PRP and RPO

I have understood the proof that shows that a PRP is a PRF except for negligible probability $\frac{q(n)^2}{2^{-l(n)}}$. My computations show me that the same argument, perhaps with minor mathematical ...
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### Lattice based cryptography implementaion frameworks in python? [on hold]

I am working in the area of lattice-based cryptography. i would like to know implementation using python in Internet of things. suggestion please.
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### How to encrypt numeric data on a ticket

I have a customer with an existing ticketing system that generates tickets for events like theaters, movies, football and so on. The information in each ticket is encoded in a 16 decimal digit ...
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### DES/AES invertibility

My professor has posted a couple of practice questions that so far I haven't been able to find the answer for and I was hoping you could help. DES would remain invertible—it would still be ...
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### What are some potential applications of trilinear mappings?

In "Applications of Multilinear Forms to Cryptography" Boneh and Silverberg give "one-round n-way Diffie-Hellman key exchange protocol" as a potential application of n-multilinear mappings. If we ...
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### Is reverse engineering SHA256-HMAC function possible? [duplicate]

Assume HMAC function is used to generate a 6-digt integers time-based onetime password. As follows: K_h =\operatorname{HMAC}(k,t) = H((k\oplus\text{opad})\mathbin\| H((k\oplus\text{ipad})\mathbin\|...
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### I believe this code is unbreakable [on hold]

It is not a one time pad. I can send messages to my partner in crime using only an 18 x 12 grid containing only the letters A,B,C,D,E,F - he can look at the grid I send him and using only 3 rules ...
49 views

### Algorithm for symmetric encryption (diffusion without confusion)?

I'm looking for a symmetric encryption algorithm with specific characteristic. Having a key $k$ a message $m$ returns a ciphertext $c$, where $E_{k}[m] \rightarrow c$ It should be hard to perform a ...
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### If nG and 2nG are known how to find generator point G

If in a curve $y^2 = x^3+ 7 \mod p$ ( ecdsa-secp256k1) p=115792089237316195423570985008687907853269984665640564039457584007908834671663 G=...
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If the last 448 bits of a sha1 block input are known (only the first 64 bits are unknown). Is it possible to do a preimage attack using SAT solvers or something else? Or do I have to brute force all $... 0answers 39 views ### How does the user check whether$y < M$without knowing all shares? CRT-based Verifiable Secret Sharing Scheme In this paper, section 4 Verifiable Secret Sharing Scheme, the dealer phase and the combiner phase are as follows: Dealer Phase To share a secret$d \in ...

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