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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Security of ChaCha compared to AES and Serpent

I'm trying to understand how secure XChaCha20 is in comparison with other ciphers. From what I know, ChaCha is more secure than AES, but less secure than Serpent. My question is how much more "...
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How does a pseudorandom generator produce a similar distribution to $U_{n}$?

According to Wikipedia, a function ${\displaystyle G:\{0,1\}^{\ell }\to \{0,1\}^{n}}$ with ${\displaystyle \ell < n}$ is a pseudorandom generator against $\mathcal {A}$ with bias $\epsilon$ if, ...
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Stream cipher vs OTP, with /dev/urandom and secure key exchange

My application will work in an office setting where a user can directly and securely collect a long One Time Pad. For example, it may be 16Gb on a USB drive. This would fill me with joy except that ...
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Would a key recovery attack on ChaCha's keystream would be made more secure with an AONT?

To be clear I'm well aware that ChaCha doesn't need to be "improved". Also, I have no intentions or misguided ideas about trying to "improve" it. My question is hypothetical, and ...
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How to find out the block size of Xchacha20 in Libsodium?

I heard that Xchacha20 works like a block cipher so that even if it wants to encrypt one byte, it will do the work of at least one block. So technically it works similar to a block cipher in counter ...
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Usage of block and stream ciphers

I see that in many applications stream ciphers are common than block cipher - whether is Salsa20, AES-GCM, etc. In which cases would a stream cipher be preferred over a block cipher and vice versa? ...
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Stream cipher and block cipher usage in network data encryption

Stream ciphers are usually used for streaming data encryption, such as voice, and also for low layers data encryption. For example, MACSec uses AES-GCM encryption. In L3 ad L4 security protocols (...
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Having two messages and a result ciphertext, is it possible to know which one was encrypted using One Time Pad?

I have two messages $m_1$ and $m_2$ and a result ciphertext $c$, one-time pad was used to create the ciphertext $c$, is it possible to know which message was used to generate the ciphertext $c$?
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Is a stream cipher and a (cryptographically secure) PRNG nearly the same thing?

If I let the authentification tag aside (which is important), encrypting with AES-GCM and a fixed key and nonce: ...
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Breaking the 40 bit DVD CSS stream cipher

This is from the transcript of Dan Boneh's Coursera Crypto course https://www.coursera.org/learn/crypto/lecture/mQAkP/real-world-stream-ciphers So it turns out this is easy to break in time roughly ...
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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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Stream Cipher Key Stream from Successive Hashes

I'm currently studying crypto and wondered what would be wrong with the following process... I want to encrypt a long message $M$ with a short symmetric key $K$ and a public nonce $X$. The idea is to ...
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OFB output jth-block expression clarification

Stalling says: OFB encryption can be expressed as Cj = Pj⊕E(K, Oj-1) where Oj-1 = E(K, Oj-2) Some thought should convince you that we can rewrite the encryption expression as: Cj = Pj⊕E(K, [Cj-1 ⊕Pj-...
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How to increase Poly1305 performance?

I was analysing the Chacha20 algorithm and the Poly1305 MAC generation from RFC 7539. It seems that the Chacha20 is quite faster compared to AES on CPUs without hardware support like AES-NI. But ...
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Text cipher option that can decrypt the same ciphertext to two DIFFERENT and DESIRED outputs given DIFFERENT keys (and/or alphabet)

I have a pen pal that I discuss with. In our latest discussion it was proposed to write a short message that is ciphered and have the other one find what it is, given some clues. I would like to ask ...
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Is it possible to acquire the next keystream of Salsa20? (If you know part of the keystream)

When you know the Salsa20's keystream, how do you know the next keystream? In other words, can I infer the next keystream when I don't know the Key and IV of Salsa20, but the keystream is ...
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Pseudorandom Generator

In a cryptographic application, two types of (pseudo)random bit streams are needed: a stream $A= a_{1}a_{2}a_{3}\ldots$ in which $\Pr[a_{i}=0]=\Pr[a_{i}=1]= 1/2\ \forall i$ and a stream $B= b_{1}b_{2}...
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Can repeatedly encrypting a message with a secure cipher ever produce the original input like what happens in ROT13?

Lets say we have a message 'm'. We encrypt 'm' using a stream cipher or any other type of cipher with cryptographic security that produces an output equal in length to the length of 'm'. Then if we ...
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Should you pad messages encrypted with stream ciphers?

Should you pad messages encrypted with stream ciphers? The obvious answer seems to be yes, right? It obviously leaks the exact length of the plaintext. Consider a situation where an adversary knows a ...
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Is precomputing AES-CTR key stream secure?

Q0 : Is the precomputed key stream vulnerable to side-channel attacks like a lookup table for exemple ? I don't think it is because a lookup table is accesed very often, that's what makes it non ...
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ChaCha matrix - tests for original implementation not passing due to bad counter encoding?

Hello everyone and already thanks for taking your time to read this! I am currently implementing ChaCha20 (256-bit key) for my bachelor thesis. I know that there are two version of ChaCha out there; ...
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Number of keystreams generated in Kreyvium for a single key/IV pair

Kreyvium employs 128-bit key and 128-bit IV. By a single initialization procedure using a key/IV pair, how many keystreams can be generated?
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ECRYPT Salsa20 Test Vectors Interpretation

I am currently implementing Salsa20 for my bachelor thesis. After having verified all the functions needed for the final encryption function with the given test data in the specification from DJB, I ...
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Encrypting a string of arbitrary size with a big integer

I am currently writing Python script that initiates a secure handshake. I am kind of reinventing the wheel here, so that I can properly learn it. Now, I have Diffie-Hellman mostly working from ...
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Logarithmic brute-force for stream-ciphers

First of all, I want to make sure I understand stream ciphers correctly: I put a plainchar (e.g. byte?) through the stream cipher and receive a cipherchar. Correct? When I now have a pair of ...
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Hash based stream cipher where the input is a constant, key, nonce and counter

This is a question out of curiosity ! A hash function produces an output that is considered computationally infeasible to reverse. Let's consider, for the sake of illustration purposes a tried and ...
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Approach used with XOR cipher in black box scenery

What's the approach used in cryptanalysis to make an decrypter for a simple xor stream cipher in a Black Box scenery with only the output?
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Question about ChaCha20's security

I wonder the Stream Cipher ChaCha20 only changes 96 bits each block, why it can produce 512 bits keystream block, I mean in the concept of a random number generator, the ...
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Can we use a hash-based stream cipher against DPA attacks?

There have been lots of DPA researches against block ciphers. I was wondering if we use a cryptographically secure hash of an incremental counter as a stream cipher, will it withstand DPA attacks? ...
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Linear approximattion of $(x+y) \bmod 2^n$ in FSM of SNOW 2.0 where $x,y$ in $F_{2}^n$

I would like to understand the linear approximation of $(x+y) \bmod 2^n$ by linear masking method in the paper refereed ""Improved Linear Distinguis'hers for SNOW 2.0" by Kaisa Nyberg and Johan Wall´...
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Most used stream ciphers?

I am writing my Bachelor thesis on topic "Current state of stream ciphers". So my questions is: Which stream ciphers are used the most. So far I have A5 family, RC4, E0 (Bluetooth), Snow 3G and ZUC (...
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Can Trivium ciphertext be decrypted by an adversary if the key is known, but the IV is not?

Suppose that the adversary is able to recover the key of Trivium cipher. But the associated IV is unknown to him. Will he be able to decrypt the ciphertexts without any complexity?
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Which cipher is used in the new 5G network?

I think that the stream ciphers SNOW 3G and AES are used in 4G (LTE). But I can't find which cipher is used in 5G networks and how encryption is done. Is there any official documentation?
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Best method for storing cryptographic secret key and generation of IV in Trivium?

How the secret key for Trivium cipher is stored and managed in an embedded system (IoT sensor node)? How the IV is generated in a Trivium? How to justify the fact that storing a fixed value (for ...
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What is the significance of IV in stream ciphers like Trivium?

In Trivium cipher, an 80-bit key and 80-bit IV (initialization vector) are used initially to set up the initial state. I would like to know, Role of IV in stream cipher? Can we make IV a secret ...
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Attack on LFSR key stream generator

Alright this is a question I found on one of my books: Given is a stream cipher which uses a single LFSR as key stream generator. The LFSR has a degree of 256. How many plaintext/ciphertext bit ...
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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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