# 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 there any format-prolongation encryption?

Given plaintext $m$ of length $l_m = |m| > 0$ After encryption $E$ $$E(m) = c$$ we receive a cipher $c$ with an elongated length $l_c = |c| > |m|$ With decryption $D$ $$D(c) = D(E(m)) = m$$ ...
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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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### 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 ...
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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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### ring signature with embedded data

As part of Spontaneous Anonymous Group (SAG) signatures of say 16 participants, the prover generates fake random responses for 15 elements and a real response at some secret index. I want to hijack ...
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### Zero knowledge proof for the verifiable encryption

My question is about the verifiable encryption (Camenisch-Shoup). in the Paillier cryptosystem, a message $m$ is encrypted using a public key (composed of $N$ and $g$) and a random number $r$, ...
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### Is it a bad idea to use the same password and container size for multiple veracrypt container?

I'm new here and have a basic question about encryption. I plan to securely store sensitive data on a company computer. Being one of hundreds little branches of a bigger company, it is not possible to ...
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### What does "192-bit equivalent" mean for WPA3?

In the Wikipedia page for WPA3 enterprise mode, it states that WPA3 has an "...equivalent 192-bit cryptographic strength in WPA3-Enterprise mode..." yet it also says that it uses AES-256-GCM ...
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### Privacy-Preserving User Tracking Across Systems with Homomorphic Encryption or hashing

I'm working on a project where we have three different software systems—let's call them A, B, and C. Systems A and B handle user data identified by phone numbers and want to send user actions to ...
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### Cannot get RSA encrypt and decrypt to work in hardware and online calculator

I am attempting to get a hardware implementation of RSA working but I am having trouble with encryption and decryption. First, I ran these commands to generate the keys: openssl genrsa -out private-...
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### How to prove that signature hash is wrong without reveal message

Let's say we have Bob, Alice and third party. Bob make message signature hash and upload to third party, then encrypt message with Alice pub key and send it to Alice Alice receive message and decrypt ...
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### Possible to encrypt message without knowing recipient public key?

Assume Bob is sender and Alice is future recipient. In ideal situation Bob know Alice public key, and encrypt message with it. But what if Bob don't know Alice public key (he only will know Alice ...
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### which DH protocol is safer in communication with given condition?

I am trying to understand some concepts such as DH problem and its variants. I have the following question from the book I read. (note that I translated the question from my language to english) ...
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### Input/Output size of compression functions

I know that DES has 56 independent key bits, and that 3DES has 168 independent key bits by using 3 separate 56-bit DES keys. 3DES also has a block size of 64 bits. If I use 3DES as the underlying ...
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### Safety of using non-encrypted hashes to identify encrypted data in a key-value store

I saw posts tangentially related to this, but not this one specifically. I'm building a content-addressable storage layer where I'd like to store the contents encrypted. The question is what is a safe ...
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### Source of encryption scheme used in blockchain based IoT

I've found the following encryption scheme UserA: $$sk_A, pk_A = sk_A \cdot G$$ UserB: $$sk_B, pk_B = sk_B \cdot G$$ Enc: UserA u \in \mathbb{Z}_q^* \\ Y = u \cdot pk_B \\ S = H(U) \oplus m \\ C = (...
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### ElGamal signature scheme problem and unsure whether my calculations are wrong or that's the answer

Trying to solve problem with verifying a message through the ElGamal signature scheme and I end up getting two different values. I'm given a prime number p=881 , e1=3, d=60 , and a random value r=11 . ...
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### Assistance required with a suspected Nihilist Cipher text associated with a 1948 Cold Case [closed]

I have found a cipher text that shows up as a Nihilist Cipher when entered into the dCode cipher identifier. The text was found in a torn slip of paper bearing the words TAMAM SHUD, the last two words ...
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### Does combining a stream cipher and block cipher produce any vulnerabilities?

In particular, AES-CBC with Blake2b for HMAC combined with xChacha20-Poly1305. The scheme is to encrypt with xChacha20-poly1305 first, using a key derived from a high entropy password using argon2id ...
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### Does using multiple encryption algorithms with different keys on the same cipher text improve security?

I'm looking for maximum possible security. My current scheme is xChaCha20-Poly1305-xSalsa20-Poly1305-AES-CBC-HMACSHA-512. Does combining these algorithms increase security if implemented correctly? ...
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### Is it secure to encrypt an authentication token using another possibly hashed authentication token?

I'm working on a web app ("main") which acts as a central access hub for several other web apps ("children"). The users are supposed to authenticate in the main app, resulting in a ...
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### Is gcd(e,p−1)=1=gcd(e,q−1) similar to gcd(e,phi(n))=1?

I wonder, is $\gcd(e,p−1)=1=\gcd(e,q−1)$ similar to $\gcd(e,\phi(n))=1$ ??
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### Does the use of a passkey (FIDO) link your physical device id, eg IMEI, to that specific passkey?

Passkeys are being introduced. From what I understand so far, a passkey involves the storage of a private key, and retention of a public key with the internet service. Eg Google, Apple, Microsoft, ...
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### In RSA Encryption, Can I choose the public exponent e > m (modulus) ? or e > φ(n)? [duplicate]

In RSA ,the encryption, Can we choose the public exponent (e) greater than m (modulus) or e > φ(n) ? I wonder about choosing public key exponents (e) because the most information on the internet or ...
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If $\Pi=(\mathrm{Gen},\mathrm{Enc},\mathrm{Dec})$ is a CPA secure public key encryption protocol, is the following public key encryption CPA secure? $\Pi'$: $\mathrm{Gen'}$: Run $\mathrm{Gen}$ twice ...