Questions tagged [stream-cipher]

A stream cipher is an encryption algorithm which encrypts arbitrary length plaintext, using a key. Some stream ciphers generate a keystream from only the key, which is then XOR-combined with the plain text, others feed back plaintext or ciphertext into the algorithm to create the keystream.

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Is XChacha20 - Poly1305 Quantum resistant?

This is a question just out of curiosity, as I am a newbie to Post Quantum Cryptography. I have read several articles where they emphasize that current standardised symmetric encryption algorithms (...
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Which is the best algorithm for large scale file encryption other than AES?

I've been looking for a fast, powerful and robust algorithm for encrypting large files with authentication . I would like to implement the algorithm on my own without using third party software. I've ...
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Storing values under different keys (e.g. during key rotation)

If you are encrypting some secrets (database passwords, access tokens, etc). When it comes to key rotation, you'll need to store those encrypted values twice, for a short period of time (under the ...
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Name for a Ceasar Cipher that uses random offsets?

In a traditional Ceasar Cipher, you pick a specific offset such as "plus three" so that to encrypt each character of a message you count three letters up from the input and to decrypt you count three ...
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How to calculate period of stream cipher with multiple LFSR and NLFSR

I am interested in knowing how to calculate period of a stream cipher with more than one FSR (linear as well as non linear). I know for a single FSR, period can be calculated with farmula q^L-1 where ...
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Are there any state of the art crypanalysis tools for stream cipher

I am new to cryptanalysis and interested in knowing cryptanalysis tools (black boxing or white boxing) for (not any specific) stream ciphers in general sense. Scenario: I am given an assignment to ...
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Use large key size for RC4 to avoid RC4 bias

I saw a question on StackOverflow where RC4 was initialized by a 1024 bit key (with 2048 the maximum key size, if I'm not mistaken). Will such a large key size possibly solve any of the bias of the ...
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Can we use the same frame counter in A5/2

Let we have three encoded messages with length $3*456$ bits in A5/2 encryption. Can we use the same frame counter in the encryption process or we must use different? (E.g. this because in the below ...
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How to prove IND-CPA on a cipher [duplicate]

I came across an exercise "custom" block cipher which looks like a counter mode implementation, but it is not exactly it. I want to check if this scheme is IND-CPA secure. Here is a picture of the ...
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Is the ChaCha20 block function reversible using known plaintext?

I've been recently implementing the chacha20 stream cipher with Poly1305. As the core operations which make up the Quarter Round of chacha20 (ARX - Addition Rotation Xor) are indeed reversible, does ...
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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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Is there any security issue if an attacker recovers the key stream generated by a stream cipher?

I've learned that a stream cipher like ChaCha20 generates a key stream that gets XORed with the plaintext to get the ciphertext... If an attacker knows the plaintext, he could just simply XOR that ...
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How does stream cipher works? [closed]

I will be grateful if someone can explain how stream cipher works using Pseudorandom generator(PRG).
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Recognizing and decrypting custom cipher with known plaintext and ciphertext

I've been trying to reconstruct an encryption algorithm that produces a known ciphertext from a know plaintext. I have done some analysis: the algorithm operates on single bytes a plain text can be ...
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Circular Security - Encrypting the key with the key

I know this isn't the best practice, but what if I took a cheap/fast 128-bit stream cipher (assuming both the key and the stream blocks are 128 bits) and mixed in the plainkey with the plaintext (let'...
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Stream cipher - Many time pad

I understand the concept that when you xor the cipher texts you get the XOR messages cause the keys get XOR-ed and cancel out... This is at least the case when both the messages are of equal lengths. ...
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A5/2 session key derivation

Let talk about Implementation and performance analysis of Barkan, Biham and Keller’s attack on A5/2. In this paper, mentioned that we need to brute force attack on register 4 ($R_4$) to get keystream ...
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Design of SIMD-implemented cipher

Design of efficient of block ciphers needs consideration of many factors such as register size. i found that some ciphers can be SIMD implemented such as TWINE , SM4 , chacha20 ,SPIX ,and others. ...
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Safely store data before moving to air-gapped machine

This is related to an earlier question, Is it possible to use an algorithm to generate an OTP? I have two machines: A, and B. A is connected to the internet and files are uploaded regularly. B is ...
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What happens after sharing the secret key in quantum cryptographic schemes to send the message bits?

As a person working on the physics perspective of quantum communication, I understand the process upto which the quantum key is shared securely. What happens after this process to send message bits? ...
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How can AES-CCM behave as an AEAD stream cipher?

AESCCM- Couter with Cipher Block Chaining Message. As it uses cmac for generation for tag , which is internally aes-cbc (block cipher, need block size, may require padding) And Encryption is done ...
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Meaning of direction in EPS

In EEA (EPS Encryption Algorithm) and EIA (EPS Integrity Algorithm), what exactly does the direction (uplink/downlink) indicate? It's confusing because for both encryption and decryption of a given ...
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Can Trivium be used as a PRF?

The Trivium encryption algorithm has two inputs, key and IV, both of which are 80 bits long. Let's call it Trivium(key, IV) → keystream. My question is whether doing Trivium(key, input) and taking the ...
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Perfect Forward Secrecy Stream Cipher based on Block Cipher

I'm thinking about ways to encrypt an endless stream of data (e.g. a video or audio feed) in a way, where a compromise of the current internal state of the encryption (e.g. a RAM dump) does not ...
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AES Stream Cipher Mode Key Reuse With Random IV Per Message [duplicate]

Im using AES OFB mode, which is a stream cipher. It will be used to encrypt many seperate small amounts of data in very short amounts of time. If for every separate piece of data encrypted I use a ...
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Building Key Streams from PRNGs

I am reading an intro book about cryptography and the author tries to explain why using pseudo random number generators is vulnerable. Given PRNG equation; \begin{align} S_0 &= \text{seed}\\ S_{...
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Building Key Streams from PRNGs [duplicate]

I am reading an intro book about cryptography and the author tries to explain why using pseudo random number generators is vulnerable. Given PRNG equation; ...
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Understanding LFSR stream ciphers and the content scrambling system

I'm a little confused over how exactly Linear Feedback Shift Registers (LFSR) work, I kind of get it, but not really, can someone help me understand it? I know it XORs bits in a loop against some mask,...
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A5/1 Formula Question's

So before I start I'm learning how this algorithm still works so my first question is for the x,y, and z steps (of getting the keystream I believe). The formula is t = y 20 XOR y 21 for y. There is ...
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Is it possible to find what is the random generated key if I know the plaintext and ciphertext? [closed]

Is it possible to find what is the key with only plaintext and ciphertext? For example, My plaintext is: hi My ciphertext is: 0x1db5
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Test for true random number generator

For my networks project I have decided to implement a youtube-based secret key generator used in creating a self-synchronizing stream cipher hash function. Basically all the youtube video comments ...
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MULalpha and DIValpha operations in SNOW 3G

I'm not able to appreciate the importance of mul alpha and div alpha operations in feedback polynomial of LFSR in SNOW 3G. What problems or weakness do they help in mitigating and how ?
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What does MULx operation in SNOW 3G correspond to?

According to the spec, MULx operation is defined as - MULx maps 16 bits to 8 bits. Let V and c be 8-bit input values. Then MULx is defined: If the leftmost (i.e. the most significant) bit of V ...
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Confusing terminology about stream ciphers

In their book, Understanding Cryptography, on page 37, Christof Paar and Jan Pelzel write: Definition 2.2.2 One-Time Pad (OTP) A stream cipher for which the key stream s0,s1,s2,... is ...
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Does the bias in RC4 drop asymptotically further in the keystream?

It's well-known that the RC4 keystream has significant biases that become less prominent later in the keystream. The most severe bias is in the second byte, which has a 128-1 bias towards zero. Other ...
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secure “related-key” stream cipher

Consider a stream cipher $E(k)$ which takes a key $k$ to produce a pseudo random keystream. It should have the property that you can easily generate a set of at least 3 different keys $\{k_m, k_0, ...
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collision resistance of a composed hash function

Given a collision-resistant hash function $H(x)$, say SHA256, and I devise another hash function by $H'(x)=\sum^{m}_{1}H(x||i) \mod p$. The summation is defined on finite field of prime order $p$. ...
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Does anyone sell a proprietary symmetric encryption alogirthm?

I know that the majority of people use standardized encryption ciphers such as AES-256, and for good reason. But what I want to know is if anyone has come across a company or organization that is ...
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Why Stream Ciphers can be slower in software than Block Ciphers

I made some tests on virtual environment (Virtual Box) using StrongSwan, a VPN based on IPSec. I had latency results using ping command saying that Chacha20 (stream cipher) had poor performance ...
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Append data to authenticated ciphertext encrypted using a stream cipher

Say we have xSalsa20 authenticated using Poly1305. If $ X $ is the ciphertext, $N$ is the nonce value, and $H$ is the authentication tag such that the final ciphertext is $ N || X || H $, then given ...
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Mixing Cipher Lower Bounds

Let Z be a cipher system consisting of three m-sequence linear feedback shift registers (LFSR) of length 128 bits each which are assumed to be not cryptographically secure and the registers are seeded ...
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How to find the key of XOR encryption in Java?

I am trying to find the key of an XOR-encrypted string in Java. It is very probable that the key is eight characters long. I have the encrypted string. I do not understand how to go backwards and ...
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Ciphers based on Keywords

I am looking for different ciphers that use a key word (like "hello" or "awesome") to encrypt a given text. I know about the Keyword Cipher already; I'm looking for others.
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What are the implications of XORing ciphertext with plaintext?

I was intrigued by this question: Does adding complexity mean a more secure cipher? And it led me to wonder: What are the implications (if any) of XORing a ciphertext with the original plaintext ...
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Stream cipher — Are all random bit generators suitable for stream cipher?

I learned the stream cipher using LFSR in the book. I wonder whether all random bit generators (i.e. BBS, Rabin generator) are suitable for stream cipher. I search using keywords "stream cipher" and "...
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How resistant are stream ciphers like Salsa20 or ChaCha in a post-quantum world?

What kind of quantum computer would be required, if it is possible to break such ciphers?
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Simple but secure hand cipher for a computerless world [closed]

this is my first time posting here, so please be gentle! As may be obvious, I'm an amateur who knows very little cryptanalysis. The goal I've been playing around trying to make a simple but strong-...
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Can I achieve data authentication with ChaCha20 without MAC?

My case is rather special. I need to send data in small chunks, each under 32bytes. ChaCha20 state is 64 bytes. Since I will be receiving data stream in chunks, id like to verify it on the fly (i.e. ...
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Does ChaCha20 counter actually increment through iterations?

RFC defines: state = constants | key | counter | nonce Suggested on multiple places is to set counter to 0 or 1. It is still ...

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