# 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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### What if an AES Whitebox 1024-bit (or larger key) is created? Does it increase complexity consistently?

Following the Chow et al paper and Muir's tutorial, I was able to implement the AES algorithm using tables embedding keys of 128, 192 and 256-bit sizes, later extended to 1024, 2048 and 4096-bit sizes....
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### 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 ...
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### Multiple sender single receiver Encryption

I had this article given to me by my teacher, and I would like to enhance it. It's titled Modified El Gamal Algorithm for Multiple Senders and Single Receiver Encryption. I planned on having the ...
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### asymmetric encryption with rekeying in an untrusted environment

Alice can retrieve asymmetric encrypted messages (let's call one of them C1 and the Message itself M) for her from an untrusted environment (let's call it Eve). She owns her private key K1 and has ...
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### Filling an encrypted disk

For a full-disk encryption setup, with a physical disk X and the induced logical volume X_crypt, there are several ways to initially fill the disk: (A): Fill X with zeros; (B): Fill X with random ...
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### RSA encryption extremely large public exponent

I'm trying to do learn a bit about RSA by doing CTF's and now I am doing one problem probably more than 7 hours so I would really appreciate a hint here from an expert. I have an encrypted message $c$...
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### Strongswan KDF Test

How can a KDF implementation for IKEv2 application, specifically in strongswan implementation case can be verified for conformance with NIST SP800-135, please? SP800-135 KDF recommendation further ...
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### How to break fully homomorphic encryption over integer algorithm with known cipher of same integer?

If I do encryption and decryption like this: Encryption: $\text{E}(m) = (r \times p_1+m) \bmod N$ Decryption: $\text{D}(\text{E}(m)) = ((r \times p_1 + m) \bmod N) \bmod p_1 = m$ where, $r$ = ...
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### What is the difference between Google's API-Key, OAuth Client ID and AWS Secure Token Service

What is the difference between Google's API-Key, OAuth Client ID and AWS Secure Token Service? Are they are all just providing delegation tokens, except they are from different companies? Is there a ...
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### Encryption: am I doing it right?

I'm trying to get a per-user encryption key scheme off the ground and need some validation from wiser crypto pros. Consider the following procedure: User provides registration information to include ...
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### Private key which becomes invalid after specific timestamp

Sorry for my dumb question, as I'm not crypto guy. Is there any algorithm, which allows to encrypt some message with the public key, but the associated private key is only valid for specific period ...
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### ECDSA Message Recovery from Two Encrypted Messages with Signatures and Public Key

I am currently working on a problem where I have two encrypted messages, their corresponding signatures, and the public key. Furthermore, the value of $r$ is the same in the two signatures. I am ...
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### Gate count for Ring-LWE

In one of my recent research, I need to compare the number of gates needed in Ring-LWE encryption to AES in the circuit model. For AES we can find some estimation like this site, but for Ring-LWE we ...
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### Double encryption : what method is the best?

Given the block-ciphers defined as follows : $1.$ $C=$ $E_{k1}($$E_{k2}$$(M))$ $2.$ $C=$ $E_{k1{\oplus}k2}$$(M)$ $3.$ $C=$ $(E_{k1}(r),E_{k2}(r$ ${\oplus}$ $M))$ where $C$ is the cipher ...
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### Private Key Sharding - How is it Secure in a Distributed Network?

In a Distributed Network in order for a private key not to be compromised sharding will have to take place off the network, correct? If so: Why is it when a Distributed Network shards private keys ...
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### Can one design an asymmetric encryption scheme based on any secret sharing scheme? Are they that closely related?

I've seen both asymmetric encryption and secret sharing schemes based on graph 3-coloring, and I'm curious if this is a coincidence due to some peculiar property of graph 3-coloring alone.
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### Question on nCPA Security and Uniform Permutations

I feel I am misunderstanding the idea of nCPA security and its relation to uniform permutations. In particular I've been reading the paper "Hoang, Morris Rogaway; An Enciphering Scheme Based on a Card ...
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### Why does the Content Scrambling System have two different length LFSRs

CSS uses two LFSRs of length 17 and 25. If we have two periodic functions $f(t)$ and $g(t)$ and consider the function $h(t) = (f(t), g(t))$, then $h$ will have period $pq/\gcd(p, q)$ where $p$ and $q$...
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### permutation cipher definition unclear

I have an assignment to decode a permutation cipher based on a key. But on the internet I found only ONE website talking about it. Things are not very clear. I understand that I have to reorder the ...
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### Signal: Ratchet & Message History

Hi folks– new to cryptography. My understanding of the double ratchet algorithm (or even just any ratchet algorithm) is that it uses all of the previous state (in Signal's case, all the previous ...
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### how to compute Bit Independent Criteria on a 4-bit S-box?

The idea of Bit Independence Criterion (BIC ) was introduced by Webster and Tavares . For a given set of avalanche vectors generated by complementing a single plaintext bit, all avalanche variables ...
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I am currently working on a hardware project that will utilize the native USB and keyboard emulation capabilities of the Teensy device. Essentially, the user will store an encrypted password database ...
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### Turn a homomorphic encryption scheme into one that doesn't have the homomorphic property

Homomorphic encryption is a form of encryption that allows computation on cipher-texts, generating an encrypted result which, when decrypted, matches the result of the operations as if they had been ...
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### Example of an attack on a message exchange which uses the homomorphic property

Can someone give me an example of an attack on a message exchange using this encryption scheme, that uses the homomorphic property? In my opinion, Existential forgery under directed message attack ...
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### What are the advantages and drawbacks of using long term private keys compared to session keys?

What are the advantages and drawbacks of using long term private keys compared to session keys?
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### XEX vs EME mode of operation

Two of the CAESAR finalists use XEX and EME mode of operations (COLM uses EME, OCB uses XEX). I did literature to summarize the main advantages / disadvantages but I could not find much. My question ...
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### example of increasing size weakening security?

I'm seeking an example of a cipher construction with two variants differing by key/block/state size yet sharing most of the internal structure. Where the larger varient is easier to break than the ...
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### Is it possible to re-cipher with Paillier?

I know that with ElGamal we can re-cipher and get a second ciphertext equal to the first. Is it possible with Paillier too? When saying "re-cipher", I mean "A sends me a message, that is encrypted ...
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I am new to cryptography esp, homomorphic encryption. I would like to know if the following is possible using something similiar to additive homomorphic secret sharing. Please apologize me if its too ...
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### Homomorphic encryption - addition for more than two parties

I have just found out about the homomorphic encryption and I was wondering how is it possible to perform an addition for more than two parties? More concretely, I want to have several parties $P_i$, ...
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### Elliptical Curve Cryptography benchmark test

I have built web app that implement Elliptical Curve Cryptography. During testing using data set that i chose on my own, it already run well.. But, for now, i want to test it in some benchmark test, ...
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### Any algorithm with a pair of master keys and multiple pairs of subkey for a secure key escrow?

Note: This question looks like my other question — Any algorithm with a master key for decrypting private key encrypted messages? — which is perfectly answered by @real-or-random, but this one is ...
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### Custom encryption scheme for SSL

Suppose that messages transmitted over SSL are modified as follows: the message is splitted in blocks, $B_1, ..., B_m$ (each with at most $2^{14}$ bytes) for each block $B_i$ we do: ...
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### Negligible probability of failure in correctness definition (predicate based encryption)

I would like to understand why some definitions of correctness allow a negligible failure probability. i.e. the probability that decryption reverses encryption is 1 minus a negligibly small amount. I ...
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### Are there any proof of work style encryption algorithms? i.e. an encryption algorithm which takes a lot of work to encrypt, but is easy to decrypt

I'm wondering whether or not there is an encryption algorithm, or at least the possibility of one, which takes a lot of work to encrypt, yet can be decrypted very easily? I have come across this ...