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 modern encryption needlessly complicated?

RSA, DES, AES, etc., all use (relatively) complicated mathematics to encrypt some message with some key. For each of these methods, there have been several documented vulnerabilities found over the ...
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Difference between stream cipher and block cipher

I read that A typical stream cipher encrypts plaintext one byte at a time, although a stream cipher may be designed to operate on one bit at a time or on units larger than a byte at a time. (...
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Why do 5G, 4G, etc., use non-conventional algorithms?

Looking up information about 5G and the previous 3GPP standards, why have they been incorporating non-conventional algorithms into the standards? For example, AES has been considered secure for ages ...
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With sufficient randomness, is XOR an acceptable mechanism for encrypting?

I have heard criticism of various cryptosystems saying that "at their heart, they were just XOR." Is this just ignorance, or is there something inherently wrong with XOR based ciphers?
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Is it feasible to build a stream cipher from a cryptographic hash function?

A few years ago I devised a symmetric-key system that worked like so: ...
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What is the difference between a stream cipher and a one-time-pad?

A (synchronous) stream cipher is an algorithm which maps some fixed-length key to an arbitrary-length key-stream (i.e. a sequence of bits): $C : \{0,1\}^k \to \{0,1\}^{\infty}$. This key-stream is ...
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How to attack a “many-time pad” based on what happens when an ASCII space is XORed with a letter?

I've already sent my correct solution to a homework exercise from Dan Boneh's Introduction to Cryptography class on Coursera: "Let us see what goes wrong when a stream cipher key is used more ...
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Can I use HMAC-SHA1 in counter mode to make a stream cipher?

Say I have an embedded device which is only capable of doing HMAC-SHA1 transformations (that device is, in fact, a YubiKey). Would it be secure to feed it like a block cipher in counter mode to get a ...
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Can you make a hash out of a stream cipher?

A comment on another question made me wonder about something: Assume you're on a rather constrained platform — say, a low-end embedded device — with no built-in crypto capabilities, but ...
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1answer
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Dancing confusion with Daniel J. Bernstein's stream ciphers

I know of Salsa20 which won the ESTREAM competition. This is dated of 25 Dec 2007. There is also the ChaCha20 stream cipher (cr.yp.to/chacha.html). This claims to increase the amount of diffusion ...
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Converting a stream cipher into a block cipher

The well-known Counter-Mode (CTR) mode of operation for a block cipher essentially converts any block cipher into a stream cipher. Is there a way to do the reverse? In other words, given a "good" ...
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What is the PRG period of stream ciphers such as RC4 or Salsa20?

I am confused about how long a stream cipher can be used before you should change the key. To be concrete, let me use the stream cipher based on RC4 as an example. Let's say I want to encrypt a very ...
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Combining LFSRs for Stream Ciphers: Why do we need high non-linearity?

Linear Feedback Shift Registers (LFSRs) can be excellent (efficient, fast, and with good statistial properties) pseudo-random generators. Many stream ciphers are based on LFSRs and one of the possible ...
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Are common (secure) stream ciphers CCA1-secure?

My latest question and especially Ricky Demer's comment on the answer got me thinking: This homomorphic tranformation of RSA is most likely IND-CPA and maybe even IND-CCA1, but if it could be IND-CCA1,...
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1answer
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Why do stream ciphers use a nonce?

My question maybe will be stupid, but my problem is that I do not understand why stream ciphers need a key and also a nonce. As far as I understand, the keystream is generated with the nonce. The same ...
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Theoretical pi-based stream cipher

Let's pretend that all digits of pi are known and arbitrarily long sequences of digits are trivial to get. Further, some mathematician proves that there are no patterns in pi. We could create a stream ...
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1answer
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Security considerations on “expand 32-byte k”-magic number in the Salsa20 family of stream ciphers?

I'm currently examining the NaCl library written by Daniel J. Bernstein and I noticed that the library hard codes the sigma: ...
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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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2answers
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AES GCM vs other encryption modes in embedded environment for network traffic

I'm doing a lot of research since I'm doing an internship for a company where I need to upgrade their security level. Their own protocol needs a cryptographic upgrade and I'm leaning towards AES since ...
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Definition of a CSPRNG

I am interested in what conditions are necessary and sufficient to define a cryptographically secure pseudo-random number generator (CSPRNG). Wikipedia lists two defining characteristics: It ...
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Streaming API to authenticated encryption

In regards to NaCl, I asked DJB he had any intent to add a streaming API to an authenticated cipher. His response was obvious in retrospect, that one should never release a decrypted plaintext before ...
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Are Stream Ciphers Less Secure?

This is by no means a scientific observation, but it seems to me that stream ciphers receive a lot less attention than block ciphers. Is there any reason for this? (Is it because block ciphers are ...
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1answer
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What are the methods to construct a primitive binary nonlinear feedback shift register (NLFSR)?

Given a binary shift register of $n$ bits, a primitive binary nonlinear feedback shift register will generate a sequence with a period of $2^n - 1$. While I am unable to find a paper which directly ...
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What does a stream cipher provide that cannot be obtained with AES CTR mode operation?

I can precompute the key stream for the CTR mode operation and the encryption at that point is similar to a stream cipher. So why are there stream ciphers still used and proposed after RC4? Recently ...
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Functional difference between stream cipher, XOF, seed expander, KDF, etc

This question is a request for terminology clarification. In a canonical XOF interface, the output can be extended as much as needed, but does input has to be variable-length or can be fixed-length ...
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Authenticated encryption mode for stream cipher?

Block ciphers have modes like GCM or OCB that combine primitives to provide both authentication and encryption. Are there similar constructs for stream ciphers, which provide both authentication and ...
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How distinct are the meanings of the terms “CSPRNG,” “DRBG” and “stream cipher”?

Are there universal, consensus definitions for the following terms? Cryptographically secure pseudo-random number generator ("CSPRNG") Deterministic random bit generator ("DRBG") Stream cipher This ...
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1answer
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Are stream ciphers no longer considered by NIST?

While reading NIST SP 800-90A, "Recommendation for Random Number Generation Using Deterministic Random Bit Generators", I noted that no stream cipher was included among the various specified solutions....
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Is there a way to generate sound one-time pads out of public information?

Is there a way to 'mangle' a public data-source (for example, the current date in YYYYMMDD or the top New York Times headline) to form a one-time pad that will sufficiently hide the pad's source? ...
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Word-based stream ciphers vs “regular” stream ciphers?

Could somebody explain what is the difference between "word-based" stream ciphers and the regular ones? Those last ones use pseudo-random sequences XOR'd bit by bit with the message, as far as I know. ...
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Can I safely replace XOR with ADD in a stream cipher?

In a stream cipher, the bytes of the plaintext are usually XORed with the keystream to produce the ciphertext. Would there be anything wrong with adding the bytes instead (with overflow), if adding ...
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CBC - a canonical mode, even though there are streaming modes

Why is CBC considered the canonical mode when there are streaming modes available such as CFB and OFB? One thing that I can think of is that in CBC you can easliy do range-based decryption. All you ...
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Is there any quantum resistant pen-and-paper or mind cipher?

I know about VIC and Solitare but as I understand they are not quantum resistant ciphers. Is there any quantum resistant pen-and-paper or mind cipher?
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1answer
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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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What do you call one time pad where pseudo-random numbers are used?

What is the encryption method called when pseudo-random numbers are used instead of true random numbers?
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Security analysis of Spritz?

Recently, a new cipher called Spritz has been released by Ronald L. Rivest and Jacob Schuldt. It should be a "drop-in replacement" for RC4. There are many differences to RC4, Spritz is "spongy" and ...
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1answer
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Are there secure stream ciphers that cannot be parallelized?

Are there any stream ciphers (or a deterministic random number generators, that should work as well I guess?) that cannot be parallelized? For example, if I seed it with a specific value, and then &...
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Are CFB and OFB really meant for streaming?

CFB, OFB and other modes are meant for streaming and don't require padding. Are there still limitations such as the text needs to be greater than key length?
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1answer
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True Random Number Generator by milliseconds per keystroke (TRNG-Kms)

The simplest way to generate truly random numbers for OTP keys is to measure the time in milliseconds between each keystroke on a keyboard. The randomness depends on the user typing in various speeds. ...
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Advantages of making streamcipher stream depend on plaintext?

Most descriptions that explain how streamciphers work (like the one on Wikipedia), tend to describe a model that boils down to a simple “$ciphertext = plaintext \oplus stream$”, where the stream is ...
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Can somebody help me understand RC4 Spritz? (Three Questions)

So ever since I first took a stab at understanding stream Ciphers, not one stood out more than RC4, because it's so fantastically simple. As most people reading this will know, with its fantastic ...
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How to propagate error in variable-sized message?

I want to design a scheme to encrypt a variable-length message with a secret key, to provide confidentiality. The message is a short human-readable text string with byte granularity, let's say under ...
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2answers
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Will a SHAKE128 stream cipher be vulnerable to related key attacks?

Suppose that SHAKE is seeded with key concatenated to an IV, will the 'key' stream produced by SHAKE128 vulnerable to related key attacks like RC4 is? My guess is no because seed is already "...
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1answer
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Specification of the scream stream cipher is unclear

I am implementing in C++ the Scream stream cipher. The Scream family is composed of Scream-0, Scream-S and Scream-F. For this question, assume that I'm using Scream-S. The specifications of the ...
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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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Why is Vigenère Autokey self-synchronizing?

According to the Wikipedia, and to several of our school study materials, Vigenère autokey ciphers are considered to be self-synchronizing stream ciphers. If I understand it correctly, the main idea ...
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Is any decent RNG acceptable as a stream cipher?

I have a function f(x,n) that takes a 128-bit key x, and generates n bytes of pseudo-random data. I've tested the output bytes this function for various keys with the NIST RNG testing suite (NIST ...
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Delayed tag checks in AES-GCM for streaming data

There is currently a GitHub discussion on .NET not supporting AES-GCM for any streaming data since releasing decrypted data prior to tag checks somehow reveals the plaintext or the AES key (or some ...
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How secure is Salsa20?

I have been hearing about Salsa20 from quite some time. It is even the favorite cipher in the ransomware world. Some ransomware used this cipher, probably because of speed. I want to know how secure ...
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1answer
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Dan Boneh's Cryptography lecture - problem with 802.11b

I am going through Dan Boneh's Cyprography lectures on Coursera. In Lecture 6 https://class.coursera.org/crypto-010/lecture/6 At 7:30 minutes, he discusses the problems with 802.11b design. I ...

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