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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Sponge Duplex authenticated encryption with nonce reuse or no nonce

With a Sponge permutation in a Duplex construction for authenticated encryption. illustration example: ascon; actual interest if relevant: keccak Suppose there is no associated data and there is no ...
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Skipping first outputs of the stream cipher

I remember reading somewhere that sometimes in some stream ciphers it is necessary to skip the first values they produce. I can't find any information on this right now. But it seems to make sense. ...
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How to crack sha256 used as streamcipher with known or guessable block

Using SHA-256 as a stream cipher appears to bear cryptographic weaknesses, however, I am not quite sure how to implement them in decryption. Assume that I have an encryption function using 64-byte ...
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Attack against stream cipher (LFSR with ASCII)

I'm reading Understanding Cryptography by Christof Paar and Jan Pelzl. In chapter 2 (Stream Ciphers) there's a question that goes like this: Assume we have a stream cipher whose period is quite short....
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What does it mean to break non-invertible stream cipher?

Let's consider for simplicity Middle-Square Weyl Sequence RNG: https://arxiv.org/pdf/1704.00358.pdf We can choose there parameter for independent stream generation, we can call it key. Let's consider ...
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How do different types of ciphers relate to each other?

I understand that there are symmetric and asymmetric (public-key) cyphers. The first have the same key used for encryption and decryption, while the second use a public key for encryption and a ...
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What is an output symbol?

I'm reading Understanding Cryptography by Christof Paar and Jan Pelzl. In chapter 2 (Stream Ciphers). There is a section talking about "Bulding Key Streams from PRNGs". They assume a PRNG ...
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Can you use SHAKE256_XOF with XOR to make a stream cipher?

SHAKE256_XOF is an extendable output function based on SHA3-512. SHAKE256_XOF can be used to create an infinite length bit string with 256-bits of security. For example: ...
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What would be the benefit of using a Stream Cipher which achieves encryption performance of 0.01 cpb using 1 CPU thread?

If such throughput could be achieved what would the benefits for a data center or IoT devices in terms of power saving. Also I was wondering if such speed was possible to be realized by a cipher, ...
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How are keys shared safely for block / stream encryption?

I've picked up a grad level computer security class. I read a brief overview on block and stream encryption. I understand and have used PGP in the past and it make since to share your public key. ...
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TRIVIUM Stream cipher how it works

Hello I am quite new in cryptography so I found Trivium stream cipher can anyone explain in basic language how Trivium cipher works
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Is there a Stream Cipher, with the ability of key reusing and what would be the advantages and applications of this kind of stream cipher?

In the case of a OTP (One Time Pad), if we encrypt two different images with the same key, then two encrypted images will be generated. Then if these two encrypted images are mixed with bitwise xor ⊕, ...
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A friend created a great Stream Cipher. How should he move forward to maybe be compensated for his work?

After rigorous testing, it seems that it can possibly be a NIST-level candidate algorithm. However, explaining or even finding the right people, experts in cryptography to talk about his invention ...
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Applicability of theoretical attack procedure in actual attack to ChaCha cipher

I was studying the theoretical attacks on ChaCha cipher here (See section 3). There is one special attack procedure which require key-IV(Initial Vector) pairs. These key-IV pairs are special in the ...
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Extracting key bit for a stream cipher

My question is little bit general. A stream cipher uses a $5$-bit key $(k_0, k_1, k_2, k_3, k_4)$, $k_i \in \{0,1\}$ for $i = 0,1,2,3,4,5$. Now the design contains $3$ generators $G_1, G_2, G_3$ which ...
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Using Chaskey as a stream cipher

Chaskey (https://eprint.iacr.org/2014/386.pdf) is a a secure, compact and efficient MAC for embedded systems and has won many benchmarks. It is built using an Even-Mansour block cipher. This block ...
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Is OFB-mode a stream-cipher?

I've seen that OFB is considered as a block cipher mode. But could we consider it also as a family of stream cipher?
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Stream Cipher proof of maximal period length for $n = 2^m$

While reading A course of Mathematical Cryptography by Baumslag et al., I have trouble understanding parts of the proof of Theorem 2.3.3, namely the necessary condition : Let $n\in\mathbb{N}$ with $n=...
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xChaCha20 Block Keys for Poly1305

So xChaCha20 has a nonce size large enough to safely use a random nonce with the same key. Poly1305 generally uses the first block of the cipher's output to generate its nonce. For xChaCha20 it would ...
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Why are stream ciphers computationally secure?

In case multiple stream ciphers exist, I'm refering to this specific instance in which you generate a key that is just as long as the msg, M, as a function of a nonce and a smaller key K. My textbook ...
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Does Wikipedia's WEP - RC4 example really demonstrate a related key attack or just an IV reuse attack?

On Wikipedia's Related Key attacks page, there is a section about WEP as an example to related key attacks. Encryption uses the RC4 algorithm, a stream cipher. It is essential that the same key never ...
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Why LFSR stream code is not suitable for encryption? [duplicate]

Why LFSR stream code is not suitable for encryption? Is there a special attack for LFSR?
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How to interpret my professor's statement about "seed" and "symmetric-key encryption"?

In the cryptography course, the professor said that: these days for symmetric key encryption, instead of sending out the key, Alice sends the seed to Bob, and then based on that Bob can get the key. ...
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Encrypt/Cipher and Decrypt/Decipher a string with a secret

In developing an app I have a simple use case in where I want to encrypt/cipher a string (it could also be a couple of bytes because it's essentially just an IP-Address). On the output I think it ...
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What would be the benefits of using a faster cryptographic system with the same level of security as AES

Essentially I'm asking, what if I have designed a quantum-proof stream cipher that is faster than AES-256? Will using less computational power for encryption/decryption be valuable to companies or ...
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How to choose between AES256-GCM, XSalsa20Poly1305 and XChaCha20Poly1305?

In libsodium, there're 3 symmetric encryption(stream cipher) which are AES256-GCM(Hardware-accelerated), XSalsa20Poly1305 and XChaCha20Poly1305(uncertain which version of libsodium add support to ...
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What is the best way to save ChaCha20 Nonce in Cipher-Image BMP file?

I have a question about ChaCha20. As far as I know ChaCha20 is a cipher algorithm that uses 4 inputs: Key (secret) Constant (not secret) Block Number/Counter (keystream block number) Nonce (random ...
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Constants of 128-bit key version of the stream cipher Chacha [duplicate]

I am trying to find constants of 128-bit key version of the stream cipher Chacha. I know for 256-bit key version, constants are 0x61707865, 0x3320646e, 0x79622d32, 0x6b206574. Are these same for both ...
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Getting the plaintext encrypting the ciphertext

Context: an encryption game from overthewire (the link to it: https://overthewire.org/wargames/krypton/krypton6.html, also good for more info) where given the ciphertext, one must obtain the plaintext....
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Can knowledge of algorithm be used to reduce anonymity?

This is a bit of a crazy hypothetical, but I think it best illustrates what I'm looking to ask. Scenario + Question There's a distributed & decentralized cloud storage network that's starting to ...
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Semantic Security Game

I need help understanding semantic security, in particular, the part on the 'game'. But first, from my understanding, is semantic security is a 'weaker' and more flexible way to determine that a ...
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Where can I find test vectors for ChaCha20 (trying to understand Wikipedia example)?

I was playing around with stream ciphers an found this Wikipedia ChaCha20 page (the ChaCha variant). What I'm lost with is how to test this code. There are no testvectors anywhere on that page and I ...
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Mifare Classic, authentification protocol question

Thanks to reverse engineering papers on Mifare Classic, one can study the authentication protocol. However, I have a problem understanding how it works. In the above document, after the reader ...
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Designing your own Algorithm

I have been told to design my own algorithm as a college assignment. What I could have come up with was a random cipher. For example: Suppose my plaintext is: AND ...
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Finding initial key of Fibonacci LFSR knowing only polynomial and output stream-cipher

I need to know whether it is possible to find the initial key of a Fibonacci LFSR knowing only length and taps and output stream-cipher bit sequence? Plaintext is not ASCII, nor some other sort of ...
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Discrepancy $δ$ in the Berlekamp-Massey Algorithm

I have a question regarding to the Berlekamp–Massey algorithm. Can someone guide me to understand the idea/intuition of this algorithm? According to the explanation in Wikepedia, in each iteration, ...
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Using whitespace to break many-time-pad stream cipher

I have a question about the first programming assignment in Dan Boneh's cryptography course on Coursera. You're given 10 ciphertexts that were encrypted with the same key and you can presumably assume ...
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Why are block ciphers mostly used as stream ciphers?

Using a block cipher with using either CTR or GCM mode gives us a stream cipher, the only difference being that CTR does not include a MAC tag or AAD but GCM does. I think these are the most commonly ...
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It possible to encrypt .bmp bitmap files using Stream Cipher Chacha20?

Maybe this sounds like a stupid question. I'm sorry for that. I just wanted to know is it possible to encrypt a bitmap image file like *.BMP, and generate the ciphertext which is an obscure bitmap ...
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Practical application of Stream cipher Trivium

We know stream cipher Chacha has practical application. Do you know any practical application of Stream cipher Trivium?
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Nonlinearity of a Boolean function with odd number of input bits

Highly nonlinear functions are used in combination generators and other stream ciphers. We know that maximum nonlinearity (hamming distance to all affine functions) of $f$ is achieved when $f$ is bent ...
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Decryption of Alternating Step Generator

I have programmed an alternating step generator in the following way: I have three LFSR. LFSR_1 is being clocked in every step. Every LFSR has an initialization vector. And we have a text to encrypt. ...
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What does that mean, that A5/1 is clocked?

What does that mean, that A5/1 is clocked? What happens if the clocking bit agrees with the majority bit?
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Is there a library that output LFSR images given parameters?

I'm looking for a library that given parameters; feedback polynomial, initial values then it will produce $\LaTeX$ / Tikz codes to include in Latex documents or LFSR images. Is there such a library? ...
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Benchmark for CSPRNG as stream ciphers?

My limitation in my security protocol is that I want my RNG as CSPRNG and I also want it to be super fast. If I use Salsa20 or ChaCha or AES counter mode, I don't get the desired speed. I want my PRNG ...
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Which test suit is better to say if PRNG is CSPRNG:TestU01 or NIST?

Actually my concern is that I am planning to apply xoshiro256+ for implementation of stream cipher https://prng.di.unimi.it/ for my cryptographic application. It passes the BigCrush tests. Will it ...
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how can identify which cryptanalysis is used ( Indistinguishability cryptanalysis against classical ciphers) [duplicate]

I have 10 ciphertexts and 10 plain texts I want to know which cipher is from which plain text how can I know this I know the name of substitution cipher, transposition cipher, Vigen`ere cipher and ...
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Is multiple encryption with stream ciphers vulnerable to meet-in-the-middle attacks?

Let's suppose I encrypt something with a stream cipher (CSPRNG) two times using two 256-bit keys and different IVs. Will I get 512-bit encryption strength?
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AES plaintext is smaller than 128 bits [duplicate]

I'm currently developing a AES implementation in a graduation project at university. As far as I know, AES uses a 128 bit block length as input . if the entered string to encrypt is not 128 bits such ...
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Are all stream ciphers algorithms based XOR with the key?

I'm new to cryptography and I try to understand more how the stream encryption works. When it comes to stream encryption I understand that the paradigm is to perform 1-to-1 bit encryption; the input ...
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