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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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 ...
8 votes
3 answers
2k views

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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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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1 answer
232 views

How to crack base conversion that uses a secret symbol set?

I've looked at this crypto SE post but it doesn't address the how of my question. I've been interested in cryptography for some time. I wrote a relatively basic cryptosystem in Python that uses base ...
19 votes
12 answers
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Is it possible to make time-locked encrytion algorithm?

I'm not sure if what I'm asking is even a valid question but here goes. Would it be possible to add a mechanism to an encryption algorithm that would mean it had to be a certain time of the day or a ...
-1 votes
1 answer
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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 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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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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1 answer
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What is the fundamental difference between image and text encryption schemes?

I don't know where to ask this question, I hope I am in the right place to ask about this. So, what exactly is the fundamental difference between image and text encryption techniques? link 1 link 2 ...
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1 answer
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What is the Standard to protect classified, Secret and Top Secret information?

Para 3 of Security Requirements for Cryptographic Module (FIPS 140-2) specifies the requirements that will be satisfied by a crypto module protecting sensitive but unclassified information. What are ...
2 votes
2 answers
321 views

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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2 answers
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Can I change the radio frequency according to my encryption algorithm?

I know that information can be changed by changing the frequency of electromagnetic vibrations.My question is, can I change the frequency according to my encryption algorithm? That way I can get a ...
1 vote
3 answers
102 views

Zero-Knowledge Proof of Encryption with a Specific Key

Short version: Given a hash of a plaintext, a public key, and a ciphertext (but not knowing the original plaintext), is there any way to verify that the ciphertext is the plaintext after being ...
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1 answer
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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 ...
2 votes
4 answers
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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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4 answers
189 views

Enigma encryption

I know how an Enigma works and that the reflector means a current flow must return by a different route but my question is this. After returning from the reflector and through the rotors, it passes ...
3 votes
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Does the following variant of functional encryption exist?

For a (possibly complicated) function $f: X \rightarrow Y$, can we design a set of encryption scheme $Enc, Func\_Enc$ such that, for $\forall x \in X$, $$Func\_Enc(f) = g \text{ where } g \text{ is ...
2 votes
1 answer
65 views

The cost of the additive homomorphic encryption of McEliece cryptosystem

Let's have two integer-vectors $v_1$ and $v_2$ that are encrypted by McEliece public key. An intermediate node between the sender and receiver receives the two encrypted vectors $\text{E}(v_1)$ and $\...
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Proving encryption scheme doesn't satisfy EAV

Hello I have a problem that asks to prove the following encryption scheme doesn't satisfy EAV security. Im a beginner in this field and I'd appreciate some help making a proof for this. The solution ...
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1 answer
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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 ...
5 votes
1 answer
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What best to put in unused nonce bytes when using AES-GCM-SIV

I want to use AES-GCM-SIV for authenticated encryption of messages in my protocol. Since it is a wireless protocol I want to transmit as few bytes as possible. For successful decryption I need to ...
17 votes
5 answers
3k views

Is a PRG more costly than AES or any other encryption standard?

I know that there are many encryption standards that take a key and sometimes an IV to produce a cipher-text (the most prominent one is AES). These standards usually involve many rounds of addition ...
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6 answers
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why XOR is recommended/Used in every paper I read for encryption and decryption stream cipher?

Stream ciphers use a deceptively simple mechanism: you combine the plaintext data, bit by bit, with “key” bits, using the exclusive or operation. Why can't I use other opeartions such as NAND, AND, ...
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Can HKDF be safely used as a round function in a Feistel Cipher

Hello my question is it practical to use HKD as a round function in a Feistel Cipher I know you should not roll your own crypto, this is for learning purpose's only. Take a look at my code and let me ...
1 vote
2 answers
323 views

Encrypting random IV in CTR mode (no nonce!)

Use of plain random-IV's in CTR mode, without any special "nonces/counters" (or any "dedicated" bits!), can lead to problems with "partial overlaps", whereby attackers ...
1 vote
1 answer
371 views

Conditional decryption

Is it possible for one party to encrypt some data and have another party (unknown to the first party) view that original data if a certain condition is met? I cannot find any information about this ...
4 votes
5 answers
5k views

Which encryption method supports random reads?

I have a file containing 16-bit samples and I want to encrypt it, but the problem is that I need to be able to read any random 16-bit value from the file, and be to able to decrypt it, without reading ...
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hashing two inputs with a single encryption

I'm looking at hash function constructions that use ciphers. There are many which are analyzed in this paper: https://www.cs.ucdavis.edu/~rogaway/papers/hash.pdf but all of them assume that only a ...
5 votes
1 answer
2k views

One ciphertext, multiple keys, multiple messages

I recently came across the following idea, does anyone know a name and if it is used? A wants to send B a message (A and B know both have a common secret key) and C wants to intercept it (without the ...
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2 answers
352 views

Symmetric Multi-Key Decryption

Is there an encryption decryption scheme in which a group of people are all given different keys, and of which each key can decrypt a file. (I’m not talking about a scenario where a file is encrypted ...
1 vote
1 answer
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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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Chaos theory combined with RSA and/or other cryptosystems? [closed]

What are your thoughts on this? Are there any complications a designer of such a cryptosystem might face? Or, a better way to put it.. are there obvious drawbacks with chaotic functions when using ...
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1 answer
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Indistinguishability obfuscation and PRFs

Consider a family of pseudorandom functions $F$, each member $f_k$ of this family is indexed by a key $k$. It is true, due to a result by Barak et al, that black box obfuscation is not possible for a ...
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What should be passed as the authentication tag when creating a SealedBox? And can it be made public?

When creating a SealedBox, one of the parameters which needs to be passed is an authentication tag: https://developer.apple.com/documentation/cryptokit/aes/gcm/...
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Authenticating a device for remote motor control [migrated]

I'm looking for a standard solution to the following problem. I've been unable to find how something like this is normally accomplished. Even a key word that points me in the right direction would be ...
2 votes
2 answers
157 views

Can you re-encrypt data without knowing what the data is or using PRE?

I'm currently working on a distributed consensus-based system. I currently give the system a private key through a threshold encryption model, and I want to be able to take some data encrypted with ...
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2 answers
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What weaknesses are worth investigating in this non-linear matrix cipher?

I have an interesting cipher based on matrix products that I've not seen before. Given plaintext bytes $p\in[0,255]$, pad to a perfect square length and write into the entries of an $n\times n$ matrix ...
1 vote
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71 views

How to instruct VeraCrypt to use my hardware entropy source

As a hobby I built a radioactive decay based RNG, that I am still perfecting. I would like to know how to use its output to contribute to VC entropy pool for key generation. I know that before ...
2 votes
1 answer
89 views

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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107 views

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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1 answer
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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, $P$ ...
1 vote
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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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2 answers
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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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1 answer
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How do the notch and window positions on an Enigma machine correlate?

I am having difficulty visualizing the stepping process. The permutation of Wheel I of Enigma I is as follows: ...
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1 answer
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Looking for a modifiable signature!

I am a graduate student and have encountered some problems in my research. When I generate a signature on the data block of the file, and the signature is composed of the user's private key, the data ...
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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 ...
1 vote
2 answers
307 views

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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