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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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Maximum security strength in bits of ISAAC cipher?

Wikipedia claims key length can be very big in this cipher, so I assume it can offer a million bits of security provided entropy of key is the same? Of course I can SHA-256 hash the key to allow any ...
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Meaning of epsilon in proving a PRG is predictable/ un predictable

I am quite confused, I have been following a course on crypto provided by Dan Boneh, this is the lecture I am confused with - https://www.youtube.com/watch?v=EjWap3szsPk time stamp 8:58 - 11:00 I don'...
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How to produce a binary output sequence using LFSRs but with increased linear complexity?

How to produce a binary output sequence using LFSRs but with increased linear complexity? I have tried searching but i got confused on equation details. So can anyone help me with rather simple ...
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How to know the difference between two ciphertexts without key stream in stream ciphers [duplicate]

If I have two cipher texts lets say $C_1$ and $C_2$ of the same length encrypted through stream cipher technique using the same keystream. Let's say they are: $$C_1: \texttt{96 C6 A1 08 E7 F2 33 3B ...
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E0 encryption algorithm attack vector

E0 is used for encrypting Bluetooth communication which is initialised with a key of at most 128 bit, How secure is E0 and what are E0 encryption attack vector?
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How to crack LFSR with known plain text attack?

I'm learning stream ciphers and I'm at LFSR cipher, and I've been trying to solve the question that states if given a 5th degree lfsr with the cipher text ...
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Maximum key stream sequence per key/IV pair in communication protocols

In the paper "LIZARD – A Lightweight Stream Cipher for Power-constrained Devices", one of the design rational of Lizard cipher is key stream size per key/iv pair. A5/1 produces only 228 keystream ...
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Self-synchronizing cipher recovery from dropped bits

This cryptography book says: There are also asynchronous or self-synchronizing stream ciphers, where the previously produced ciphertext bits are used to produce the current keystream bit. This ...
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Learning about Feistel Cipher

I'm learning about Feistel Ciphers at the moment, but having issues with the formulae, so I can't move on from it. Encryption: $𝐿𝐸_{𝑖+1} = 𝑅𝐸_𝑖$ $𝑅𝐸_{𝑖+1} = 𝐿𝐸_𝑖 \oplus 𝐹( 𝑅𝐸_𝑖 , 𝐾...
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Analyzing RC4 with a reduced state array [duplicate]

RC4 is a stream cipher which uses a 256-element array of 8-bit values. All operations are done modulo 256. Is there any research on modified versions of RC4 using a smaller state array? How small can ...
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How secure is a 4 digit seed?

When I Use a 4 digit random number(e.g. 4468) as seed for a (manual) Stream cipher and straddle it to the length of the plaintext using a lagged fibonnacci generator, can this seed be found by brute ...
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How is overflow handled in word addition steps in Salsa20?

I feel like I'm completely missing something there. The quarter-round proceeds as follows: ...
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Terminology: Is a block cipher in counter mode still considered a block cipher or is it classified as a stream cipher?

I'm confused about what terminology to use. I see people referring to such a cipher-MOO combination using both terms.
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Starting stream cypher, first block (Salsa20)

I'm implementing Salsa20 in Rust for fun. I have the initial state (4x4 32-bit matrix) setup from the key, nonce, and stream position 0. I'm using the Wikipedia Salsa20 article as reference, and I'm ...
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Are all block and stream ciphers symmetric?

I'm trying to categorize my knowledge. Can I place block ciphers and stream ciphers under symmetric with RSA/DH under asymmetric?
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Why are stream ciphers based on linear-feedback shift registers so popular?

I was conducting research on stream ciphers and LFSRs was a subtopic of my research and I was wondering why are LFSRs so popular?
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berlekamp massey feedback polynomial

I have a couple of polynomials to find. Can anybody guide me with the steps to find the feedback polynomial using berlekamp massey's algorithm. Example: Key fragment: 10100100001001101001011 seed: ...
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Decrypting Ciphertext with partial Key Fragment using LFSR and Berlekamp-Massey

Edit Does the state register (the LFSR) always have to remain with 16 bits (I'm assuming yes). If so, are we shifting the register right by one (lfsr>>1) ...
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Combining stream cipher with block cipher for disk encryption

You take something like chacha20 and use the disk block # to seek it, xor it with the data block and then encrypt it with a block cipher in ECB mode. Would this be secure? Edit: To avoid getting ...
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Permutation and modes of operation

I'm reading the book "Serious Cryptography A Practical Introduction to Modern Encryption" from Jean-Philippe Aumasson, and in the first chapter, it is written this : We can try to abstract out the ...
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Stream cipher example for an introductory cryptography course

I am looking for an easily defined stream cipher to illustrate two basic principles in an undergraduate cryptography course: not every bit of the internal state should be used in the keystream; ...
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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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how Content Scramble System (CSS) works?

As I understand, the Content Scramble System (CSS) uses proprietary 40-bit stream cipher algorithm to decrypt the DVD content My question is; where does this key come from? is it embedded within the ...
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How secure is ChaCha20? [closed]

I want to implement a stream cipher to encrypt very sensitive data in my Python code. I heard about the ChaCha20 algorithm and the PyCryptodome library , but how secure is it ?
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Why is stateful CTR slightly better than stateless CTR? Does the adversary know the value of counter in CTR mode of operation?

This might be a stupid question but is really fundamental in my understanding of CTR (I'm a newbie to cryptography theory). For CPA security, the adversary only knows the IV, and may query the oracle ...
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Attack on stream cipher that XOR's the output of two LFSRs

There are two LFSRs of different lengths: LFSR-17 and LFSR-25. LFSR-17 Initially contains a two byte seed, with a 1 injected into the fourth bit, for a total of 17 bits. LFSR-25 operates in the same ...
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Why does the Content Scrambling System have two different length LFSRs

CSS uses two LFSRs of length 17 and 25. If we have two periodic functions $f(t)$ and $g(t)$ and consider the function $h(t) = (f(t), g(t))$, then $h$ will have period $pq/\gcd(p, q)$ where $p$ and $q$...
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What algorithms to use for a secure transport protocol on devices with limited computing power

I am new to cryptography. My questions is this: I process packets on runtime. I do not have time for advanced encryption or decryption techniques that take a long time. As far as I know, going with ...
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334 views

Does an IV need to be used in AES CTR mode?

If I encrypt a message once using AES CTR, will I need an IV? Additionally, if I do use an IV, will I need to send with with the cipher text?
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Expected Linear Complexity of a sequence

Let (s) be a sequence of length n. What are the expected linear complexities of (s) and $(s)^{\infty}$ (meaning that the periodic version of s)? I have no idea of the answer to this question? What ...
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Confused by the definition of Linear Complexity of an LFSR sequence?

The Linear Complexity of a sequence is defined as the length of the shortest LFSR that produces this sequence. It also corresponds to the degree of the minimal polynomial ( i.e. the smallest ...
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period of the lfsr sequence after some manipulations

Here is the question I am dealing with. I have some sort of a solution but I need more specific results. If someone can help I'd appreciate: Given 3 maximum length (max period) LFSR's of lengths L1,...
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Which cipher text is easiest to guess the plaintext?

I know that there are approximately 2^88 diff erent permutations of 26 characters. The stream cipher A5/1, which generates a binary keystream using three irregularly clocked LFSR, and has a 64-bit key....
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is it possible to get key in One time pad if key is reused?

In one time pad, if $$\text{cipherText1} \oplus \text{cipherText2} = \text{plainText1} \oplus \text{plainText2}$$ then is it possible to find out key by 2 cipherText and plainText's X-or?
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Can we replace IV increasing from addition to XOR in CTR mode?

In CTR mode (not nonce-based), if we have ${IV}\stackrel{\$}{\leftarrow}\{0,1\}^{128}$ and want to encrypt message blocks $M_1, M_2, ..., M_\ell \in\{0,1\}^{128}$: The ciphertext is $IV\parallel C_1\...
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libsodium stream encryption [closed]

I am new to cryptography, I have used OpenSSL and its aes-256-cfb cipher before to do stream encryption, which works great. Now I am going to try ...
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LFSR Jump Ahead Algorithm

A related question has been asked and answered here. My question is specifically about figuring out C for very large J. I have searched the web and found many scholarly articles on "jump ahead" and ...
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I have this list of LibSodium primitives, which should I pick so that the implementations tend to be interoperable?

When I integrate lib sodium, into a c# project, and try to consume, encryption and decryption in a particular way, it works, but the confusion is about, which method to use while encryption or ...
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Cryptanalysis on Kasumi in A5/3 GSM algorithm— why is it broken in 2G and not in 3G?

I have read the Wikipedia article that states Dunkelman, Keller and Shamir managed in 2010 to mount a related-key attack in a pretty decent time (2hrs) with a Core 2 Duo. Why was Kasumi breakable in ...
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How can I create a stream cipher from a block cipher?

Assuming $k$ is the key (128 bit) and $m$ is the message (128 bit), how can I use the block cipher $blockenc(k,m)$ to make a stream cipher which can produce quintillion pseudo-random bits?
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Can Galois/counter mode be used for stream ciphers (Galois/stream mode)? [duplicate]

The authenticated encryption mode of operation Galois/counter mode has recently gained acceptance because of its high performance due to its inherent parallelism and no pipeline stalls. It requires a ...
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Looking for title of encryption machines book

I am looking for a title of book in the field of stream crypography. I vaguely remember, that I saw this book at online shop (maybe amazon) near 5-10 years ago. This book is devoted to electronic ...
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How does the zuc algorithm complete the synchronization?

I have already read the following documents: Specification of the 3GPP Confidentiality and Integrity Algorithms 128-EEA3 & 128-EIA3. Document 1: 128-EEA3 and 128-EIA3 Specification ...
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In what mode does Signal applies cryptography over voice and data?

I have read all of the technical documentations provided via signal and so far I have figured out that signal intitializes a common key via X3DH key agreement and manages the keys via double rachet ...
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Why is Vigenére Autokey self-synchronizing?

According to the Wikipedia, and to several of our school study materials, Vigenére autokey ciphers are considered to be self-synchronizing stream ciphers. If I understand it correctly, the main idea ...
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What happens in the MonkeyWrap-Algorithm of KetjeV2 if the input is a single block?

I am currently implementing KetjeV2 in VHDL. I have a question concerning the MonkeyWrap-Algorithm that is used in KetjeV2. The function $wrap(A, B, l)$ is supposed to work as shown below, where $A$ ...
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Message length limit induced by block counter size

Wikipedia reports the following information about the ChaCha20 algorithm: An implementation reference for ChaCha20 has been published in RFC 7539. The IETF's implementation modified Bernstein's ...
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What is the attack complexity if two stream ciphers are connected in cascade?

What is the attack complexity when Grain-128 and Trivium are cascaded? Is it 2^(256 + 128) since internal state of Grain is 256 bits and assuming that IV is unknown before encryption?
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Using weak hash functions to construct a stream cipher

I am in the awkward position of developing a secure encryption scheme that provides data-at-rest security for a very limited embedded system. The system is only guaranteed to have 4 MiB of memory (...
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What Cipher Suite in this list is the worst to use

I have a list of cipher suites I captured using Wireshark. Which one of these cipher suites would possibly be the worst to use. Here is the list. In my opinion, I choose the: ...