# Questions tagged [encryption]

Encryption is the process of transforming plaintext using a cipher into ciphertext to make it unreadable to anyone except those possessing the key. Decryption is the process of transforming that ciphertext back into plaintext, using the key.

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### Is AES a group?

The question I'm wondering is whether the AES cipher is a closed cipher (which is equivalent to AES being a group). And this question interests me due to the lack of understanding of whether it is ...
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### What do we mean when we say we need more than polynomial time many cipher texts

What does it mean when we say something like „we need more than polynomial time many cipher texts“? I understand it as „an adversarial can run for polynomial time and try as many messages as possible ...
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### Is it possible for a given plaintext and ciphertext to have two different keys? [duplicate]

This has probably been asked before but for a given ciphertext and plaintext pair, is it possible to have two different keys producing said pair? Or there are no collisions in AES, unlike hashing ...
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### Prove RSA scheme is insecure

Im reviewing my crypto and I would like to prove the following: RSA experiment where the adversary is given (N, e, y) where N = pq and p, q are two primes. The adversary knows p, q. How can I build an ...
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### equivalence between entropic perfect secrecy and single probability

i'm new to information theory. I know the standard perfect secrecy definition: $$P(M=m|C=c) = P(M=m) ,$$ for all $m$ and $c$, respectively the message and the cypher. Now, i can use the entropic ...
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### Security of using predefined shares in Shamir's Secret Sharing

This is related to Is it possible to create a mix of predefined and generated shares for Shamir's Secret Sharing?, but I have unfortunately lost access to that question and can't merge accounts ...
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### Why is firmware implementation not preferred for more lfsr based encryption schemes?

Given that an algorithmic implementation of a linear feedback shift register based encryption scheme is (much?) more secure against side channel attacks; why are hardware platforms usually used? I get ...
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### Can we be certain that Signal doesn't log metadata (e.g. message graphs)?

I know Signal uses public/private key E2E encryption to ensure it's impossible for them to read the contents of messages. WhatsApp does too, hence Signal's main attraction is that it additionally ...
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### Do I need to use unique IVs if all encrypted data is unique?

I am designing a service where each user has both a unique 256-bit private and public ID. These IDs should be derivable from one another, but only within the backend of my service (as to not expose ...
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### Encryption + EUF-CMA => SUF-CMA

Does there exist a proof (paper reference welcome) that if a signature scheme is EUF-CMA, and the signatures are always encrypted, then the resulting signature scheme is SUF-CMA? That is: let SIG be ...
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### Prove CBC-MAC scheme is not secure

I have to prove the following variable length MAC scheme is insecure for an optional review. Let $\{F_{k}\}_{k \in \{0,1\}^n} : \{0, 1\}^n \rightarrow \{0, 1\}^n$ be a PRF family. scheme Mack(m) ...
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### Prove fixed length MAC scheme is insecure

I have to prove the following fixed length MAC scheme is insecure. Im not really sure how to approach this problem. Although I do know that for this specific problem keeping one of the blocks the same ...
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### Cryptographic Proof of Showing A Construction of PRGs is Also A PRG [closed]

Let G : {0,1}n → {0,1}2n be a PRG (for every n), and let s ∈ {0,1}n. Prove that the following construction is NOT a secure PRG. Gd(s): first run G(s) = x||y (where |x| = |y| = n−bits). Then run G(y) = ...
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### What are advantages of chaos based image encryption methods over simply treating images as opaque bit strings?

For an exercise at uni I am tasked with optimizing the execution speed a chaos based image encryption algorithm 1. While I have taken an introductory class to information security, I never came ...
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### IS this scheme secure (private P[M =m | C =c] = P[M=m] and correct P[m =m']) [closed]

Message space = {1,2} Key Space = {1,2,3,4} Cipher Space = {1,2,3} M * K = C So the relations are: 1 * 1 = 1 , 2 * 1 = 2 ,1 * 2 = 2 , 2 * 2 = 1 ,1 * 3 = 3 ,2 * 3 = 1 ,1 * 4 = 1 , 2 * 4 = 3 Thanks
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### Is it possible to create a mix of predefined and generated shares for Shamir's Secret Sharing?

In standard Shamir's Secret Sharing schemes the shares are generated from randomly generated polynomials. I was wandering if it would be possible to create some predefined shares that a user would be ...
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### Devising a system that allows for aggregate computations but does not hold the single values

First of all apologies if this is not the right place. I am not very knowledgeable in cryptography but I thought you can at least point me in the right direction of research. The following is a toy ...
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### Are there asymmetric encryption algorithms that preserve equality? Are they safe to use for data obfuscation?

I have a database table that needs to be shared between multiple parties. There is a sensitive column than must be obfuscated in a way that preserves equality relationships between records. A trusted ...
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### my ciphertext and original message look like they are two different sizes

The instruction wants them the ciphertext to be the same size as the original message. The original message is "alicexoxox:bobko0oo0l:popo" I am supposed to use openSSL cli to generate a key ...
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### Prove the encryption scheme is not EAV secure

Hello I have the problem defined below and I need to prove the given encryption scheme is not EAV secure. I feel like I have most of the problem down but I'm not sure what the next step should be in ...
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### Keygen with timelock encryption so that the secret key is hidden from everyone?

I'm wondering if the following scheme (or something similar) can exist: I want to encrypt a randomly generate a public key and secret key pair, $(pk, sk)$. I would like that $sk$ is encrypted some ...
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### Cartesian Product Notation for Encryption and Decryption

I'm learning about encryption $(E)$ and decryption $(D)$ algorithms and am wondering what the following notation means, specifically the cartesian product for $E$ and $D$. $k$ represents key, $P$ ...
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### In Symmetric encryption where Alice and Bob message each other, how can both decrypt the same data?

I first posted this question on StackOverflow but they told me it belongs here instead: https://stackoverflow.com/questions/77856486/in-symmetric-encryption-where-alice-and-bob-message-each-other-how-...
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### AES CTR mode is insecure if key is chosen from a tiny keyspace

Given AES-128 with a 128 bit key, but the key is chosen such that its only last 16/32/48 bit are random rest are 0, how can i exploit this to know the key being used, given i have access to oracle ...
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### Does XOR of message $m$ with $\mathrm{Enc}$ leak any information?

Let's suppose that $(G,D,E)$ is a secure encryption scheme, that is, for any polynomial $p(n)$ and any sequence of messages $\{a_{n}\},\;\{b_{n}\}$ of length $p(n)$ $E(k,a_{n})$ and $E(k,b_{n})$ are ...
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### "Offline" Revocable Encryption, or something similar to it? [closed]

For context, I want to see how far I can go using YouTube as a (bad) cloud storage solution just because of sheer curiosity and kicks and giggles. In said journey, I came across the problem of ...
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### How does SMB authentication work?

When I learned about the inner workings of the TLS protocol and what exactly it protects a connection against, I was surprised to learn that even asymmetric encryption can be defeated by a MITM attack ...
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### Is it faster to decrypt than to encrypt in all cryptography systems? [closed]

I am using a cryptography system in which the Feistel structure and permutation cipher are combined. I am amazed by the result; decryption is so much faster than encryption. My system is working ...
1 vote
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### Semantically secure public-key encryption scheme

Suppose that $(\mathrm{Gen},\mathrm{Dec},\mathrm{Enc})$ is a semantically secure public-key encryption scheme. I define $E' = (E(e,m)\oplus m)\parallel (E(e,m)\oplus e)$. Clearly, this is now not ...
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### LLM-AI useful in chaffing?

Greetings from a newbie and crypto ignaramus. I hope that this is an appropriate forum for this question - please advise if not, or feel free to move it to another SE section. First heard of chaffing ...
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### Pitfalls of manual AES encryption for data transfer

Context I've used OpenSSL to encrypt some socket communications. I am however using some functionality from the windows API that prevents me from using OpenSSL's opaque builtin sockets, so I am ...
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### Speed comparison of encryption algorithms

I am trying to compare various encryption algorithms in terms of encryption duration, decryption duration, information entropy, NPCR, UACI, and correlation coefficients. I used a Lena 256x256 ...
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### Is this self algorithm made private key for Diffie-Hellman key exchange secure

i created a function in javascript that creates my a for the DH exchange like this: ...