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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Has Telegram security been significantly improved with MTProto 2.0?

Telegram messenger's original encryption scheme, MTProto 1.0, has been shunned by most cryptographers for a number of reasons, like being vulnerable to IND-CCA attack; being unorthodox in general, ...
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Are there any weak nonce-misuse resistant encryption scheme?

Nonce-misuse resistance seems to have two standard notions: The stronger notion: this reveals nothing unless the exact same nonce is used to encrypt the exact same message twice. In this case, the ...
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Offline Group Key Agreement - Cross Device Syncing

I have a specific use case I am interested in. I have spent the better part of the night reading research papers. I am beginning to believe what I want is not possible so I wanted to confirm here. ...
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680 views

Key size, performance, and security tradeoffs for AES GCM / CCM

AES can be used with 128, 192 or 256 bit keys and each one appears to have a performance vs security trade-off (What is the effect of the different AES key lengths?, What are the practical differences ...
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1answer
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How did the cryptographers of Bletchley Park figure out the chi stream of the Lorenz cipher?

How did the Bletchley Park code breakers figure out the chi stream of the Lorenz cipher, that was obscured in the ciphertext, which British code breakers eventually decoded? It's written in The ...
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Is AES resilient to chosen plaintext with access to related keys (key expansion primitives)?

I'm interested in knowing whether a cryptosystem is broken given access to a few primitives. $\DeclareMathOperator{\KEYEXP}{KEY\_EXP}$ $\DeclareMathOperator{\E}{E}$ Suppose that you have access to an ...
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336 views

Security proof in (Ciphertext-Policy) Attribute-Based Encryption

I am having hard time understanding the security proof in Attribute-Based Encryption, especially in Ciphertext-Policy Attribute-Based Encryption. To do reduction in CP-ABE scheme, how do I check that ...
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Is it possible to derive a homomorphic signature from homomorphic encryption

At the moment I am trying to find a practical way to implement a linearly homomorphic signature. Background: "In a homomorphic signature scheme, a user Alice signs some large dataset x using her ...
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Additive homomorphic encryption scheme without change in operator

I'm looking for an additive homomorphic encryption that the addition operator (+) in its plaintext space be the same as addition operator in its ciphertext space. (Schemes like Paillier do addition in ...
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522 views

File Encryption (EFS method)

I'm implementing (for learning purposes) a file encryptor, which uses the following method (from http://en.wikipedia.org/wiki/Encrypting_File_System). I have 3 kinds of keys: RSA public/private, AES, ...
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Why does chacha20 not use bitwise not?

Right now chacha20 and blake use constants in order to eliminate fixpoints. As far as I know however inserting a bitwise not every $n$ rounds should eliminate this ...
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How do encrypted radios perform key exchange?

I'm having difficulty finding documentation for the over-the-air protocols used by encrypted public safety radios. It seems that most systems are based on Project 25, previously known as APCO Project ...
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256 views

What public-key encryption protocol can use the same key pair as ECDSA?

Assume we wanted to use the same ECDSA public/private key pair (drawn for standard ECC parameters, perhaps P-256) for both its intended use (public-key signature), and for public-key encryption; this ...
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349 views

Homomorphic system that allows Hamming distance computation?

How can I work out Hamming distance between two binary vectors securely? I would like to know how I can apply homomorphic techniques here.
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264 views

How to make a “zero knowledge” cache/key-value store

I'd like to use a possibly insecure cache for storing expensive-to-calculate sensitive information. My requirements are: If the cache ever gets compromised it should reveal nothing about its ids or ...
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105 views

search of patterns in key schedules

I am developing a new key schedule, and there is this article (Enhanced Key Expansion for AES-256 by Using Even-Odd Method) where the authors also propose a new algorithm and one of the objectives is ...
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Can RSA re-encrypt a message without decrypting it?

The goal of this question is to allow a server/proxy to forward an encrypted message without being able to read it with this procedure being transparent to the original sender and receiver. Assume we ...
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2answers
122 views

Proving the right encrypted message was sent

Total amateur to crypto here but I've searched and searched and am at the extent of my knowledge. I've gone down several avenues to satisfy what I'm looking for but I'm just going to describe what I'd ...
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140 views

How sensitive is Tiny Encryption Algorithm (TEA) to the magic numbers?

If I needed to implement an encryption algorithm from memory, chances are I would try to implement: TEA https://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm How sensitive is it to the magic ...
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250 views

Why is this Trivium implementation working bytewise instead of bitwise?

I am currently looking into a Trivium implementation available in the FELICS framework. Parameters of the Trivium stream cipher: Key size: 80 bit IV size: 80 bit State size: 288 bit The Trivium ...
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139 views

Why are matrices so common in symmetric encryption?

Matrices have been used in symmetric ciphers since the Hill Cipher (before?) all the way up to modern ciphers such as Twofish and AES. I understand matrices can be invertible, therefore making them ...
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299 views

Encrypt using ECDH with two different EC public keys, minimizing payload size

Let's say Alice has the private EC keys $a$ and $b$, with a base point of prime order $G$. Alice computes the corresponding public keys $A = aG$ and $B = bG$, and sends them to Bob. Bob now wants to ...
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Implications of TLS-SRP client with improper N validation?

During development of a client side application of TLS-SRP, i noticed a bug that allows an attacker spoofing as the server to send custom, but non-arbitrary $N$ values, with the client accepting them. ...
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Сryptanalysis of Hill's method

The brutal ciphertext is given. The text volume is more than 6000 characters. It is known that the text is encrypted with a 7x7 matrix. Unknown key and plaintext. Is it possible to crack this code? ...
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138 views

How to overcome issues with big ciphers? E.g. with small vs. big Vigenére Ciphers

I understand that bigger ciphers show more recurring patterns and therefore should be easier (or at least faster) to decrypt as you'll have a better statistical analysis, being However, if we use an ...
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237 views

Explanation of part of a visual cryptography algorithm

I have been working on a project involving visual cryptography and I am stuck with the following problem. My question is related to this paper, AN IMPROVED VISUAL CRYPTOGRAPHY SCHEME FOR SECRET ...
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57 views

Can the hash of the ciphertext be derived from the hash of the plaintext

Let $C$ be a symmetric cipher $H$ a hash function. Alice uses $C$ with a key $k$ to encrypt plaintext message $m$ yielding ciphertext $c$. She then calculates the hash of the message $h_m = H(m)$ and ...
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66 views

Does varying ChaCha rounds add any security?

This paper introduces 'Freestyle' a randomized, and variable round version of the ChaCha cipher. It uses the concept of hash based halting condition, where a decryption attempt with an incorrect key ...
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391 views

Identifying correct cipher

I am trying to decrypt a text(~900 characters) and I started with the assumption that its a Vigenère cipher as the one of the identifier tool identified it as Vigenère cipher and also the Index of ...
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1answer
223 views

What was the key length of the Enigma?

When I type in any plaintext to an Enigma machine (Enigma machine emulator) the substitution does not seem to follow any pattern. In other words, there is no cycle in the use of enciphering alphabets (...
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Is it possible to verify attributes of encrypted content?

Let's say that Alice has this information about her, { "name": "Alice", "age": 25, "eyes": "brown" } which she encrypts with a key pair so that no one access ...
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Does Openssl 1.1.1 library supports sending multiple identities as part of PSK?

Does Openssl 1.1.1 supports sending multiple ticket identities as part of PSK? i have gone through the openssl code and i don't see that openssl supports it. could someone please confirm it if i ...
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Is there a partially homomorphic cryptosystem without an inverse (addition without subtraction, multiplication without division)?

I am learning about partially homomorphic cryptography, and was interested to see if there was a system such that one operation was homomorphic, but its inverse was not. For example, if I have two ...
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How to implement security - authenticity/confidentiality/integrity for 6/14 bits radio messages?

I just took over two radio systems (using 433Mhz) - one communicates with 6 bit messages, one with 14 bit messages. Both have a lots of transmitters and one receiver (and, yes bits not bytes). For ...
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358 views

Alternative way to provision secret in Intel SGX enclave

I have a case where I have multiple clients (non SGX, assumed safe) and server(SGX based), talking over a network. I wanted to provision a shared (per client) key which is used to encrypt and decrypt ...
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1answer
151 views

Rapid partial block decryption of compute intensive full encryption

Given a block of data D: Is there a encryption/decryption scheme that would allow me to perform a resource-intensive (compute/time/memory) encryption of the full data set with a key k, but allow for a ...
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Decryption with negligible error

In chapter 2 of Katz's Introduction to Modern Cryptography there is a formal definition of an encryption scheme. As part of this definition, the decryption algorithm is required to be perfectly ...
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91 views

Plaintext DH keys in the message header in the Double Ratchet Algorithm

I've been reading details about the Double Ratchet algorithm, and I wanted some clarification regarding the aspect of the DH public keys going out in the plain in the header of every message. Quoting ...
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2k views

Cryptography behind the Turing Imitation Key (TIK)

When browsing the internet I found out about this amazing phone. Well, it would be amazing if it was actually obtainable. It's called the Turing Phone, and it is supposed to come with as good as ...
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What are the practical impacts of Wassenaar Arrangement to crypto development?

Wassenaar Arrangement limits transport of high-grade crypto hardware/software since decades, if I don't err. What are its practical impacts in that direction? In particular, does it hinder in any ...
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160 views

Authenticated encryption with Enc-Sign-Mac

I've given a CPA secure private key encryption scheme, an unforgeable private key MAC scheme and an unforgeable public key signature scheme. I want to combine them to protect confidentiality, ...
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262 views

How does darkmail (DIME) work to hide email metadata?

While Email encryption can protect the content of an email, the metadata are still readable and can be used to gather important information about the sender and the receiver. There were several news ...
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Unknown authenticated encryption mode

I'm running through a protocol specification (LoRaWAN, pdf), and I'm puzzled by the crypto. The data is encrypted and authenticated in the following way: a unique 128-bit key is used; the plaintext ...
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251 views

How can I design a cryptographically secure, key-dependent s-box?

I would like to design a cryptographically secure, key-dependent s-box, but I am not sure how. Mainly, because I am unsure about the difference in design compared to a random s-box. What is the ...
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580 views

Avoiding known plaintext attacks with an additional XOR-Layer

Can a cipher that is vulnerable to an known plaintext attack be made secure by adding an additional XOR-encryption? That is: suppose I have an (w.l.o.g. symmetric) encryption algorithm E were the ...
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153 views

Paper about this secure P2P idea?

Two or three years ago, I was reading something interesting, but then I lost the paper. The paper described building secure and fast P2P networks (not like tor or I2P). Unfortunately, I only remember ...
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468 views

Increasing the diffusion of the AES-CBC encryption algorithm in pycrypto for python

When encryption is done using the AES-CBC algorithm, the encryption can be thought of as chaining the cipher texts with the previous ones and an IV. However, if its on CBC mode, we give our cipher ...
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1answer
255 views

Why gcd(r,(p-1)/r) needs to be 1 in benaloh cryptosystem

I recently discovered the benaloh cryptosystem. I am working with the system as it is discribed in the following link: https://en.wikipedia.org/wiki/Benaloh_cryptosystem However I need some help in ...
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45 views

GPG should you double sign?

This is not a question about whether I should encrypt or sign first, as I've read here. Rather, it's about whether I should sign, then encrypt, then sign again. Because as far as I know, there is no ...
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36 views

Secure CCA Encryption under Partial Key Exposure

I'm currently learning about chosen ciphertext attack and stumbled across a problem on CCA security. If I have an encryption scheme $(Gen,Enc,Dec)$, which is CCA-secure with $Enc:\{0,1\}^n\times \{0,1\...

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