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.

Filter by
Sorted by
Tagged with
1
vote
0answers
115 views

How does the Chop Chop attack effect TKIP?

I know that chop chop attack is because of WEP's insecure checksum mechanism that is CRC32. As TKIP uses MIC along with CRC32 which just makes an attacker to wait for 60 sec upon two mismatch MIC ...
6
votes
2answers
2k views

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 ...
6
votes
2answers
3k views

Is the CBC mode of operation a stream cipher mode?

I am taking a class on security systems. My professor considers CBC to be a stream cipher mode, like CFB and OFB. Most sources I have read do not agree with this, so I asked my professor about this, ...
2
votes
2answers
745 views

Are Two Ciphers Better Than One? i.e. RC4 and AES

OK It's cringe time (or hopefully not) I know this is probably a variation of an old and dragged out question or so you may think but let me ask away and hopefully get some insight. Google a while ...
5
votes
1answer
504 views

Combination of two stream ciphers

Recently, I've been wondering what happens when I combine two stream ciphers $f_1$ and $f_2$ by xoring the keystream, so the final cipher would be: $C = P \oplus f_1(K_1) \oplus f_2(K_2)$ $P = C \...
3
votes
1answer
1k views

What if message is longer than keystream ?

I have read that stream ciphers can be used to encrypt messages/streams of arbitrary length (cf. the description of the stream cipher tag). However, there are stream ciphers that create a keystream of ...
0
votes
2answers
437 views

How to calculate the key size of my cryptographic system

I have a 'for fun' project, which is a pure software based redesign of the Enigma I. I'd like to compute the key length of my design, but I need some help with that. I have a write-up here (see ...
2
votes
1answer
146 views

Seeking key stream as way to reuse a key

In order to reduce the amount of key exchanges, I propose to encrypt messages using the same key stream, by selecting subsequent positions in the keystream for the separate messages. I.e., message $...
-2
votes
2answers
690 views

Relationship between a key stream having a high entropy and whether it is cryptically secure in a stream cipher

Hi i am trying to build a key stream generator for my homemade stream cipher.The key stream output has a close to maximum entropy value and a large periodicity. What does it take for this generator to ...
7
votes
2answers
570 views

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?
4
votes
1answer
326 views

Negating the risk of a random 64-bit nonce

Given a stream cipher such as Chacha20, which uses a 64-bit nonce, it would be unsafe to use a random nonce because of the risk of accidental repetition (which if used twice with the same key would be ...
-1
votes
1answer
259 views

Why using a nonce not more than once in SSL/TLS [duplicate]

Why it is highly recommended to use a nonce once and only once in SSL/TLS? Same question with key streams in stream ciphers? What sort of attack(s) could take place if ever a nonce/key stream is used ...
-2
votes
1answer
356 views

Elliptic curve cryptography for encrypting audio [closed]

I want to use ECC to encrypt audio. Is ECC encryption a stream cipher or block cipher? I'm encrypting one sample (1 byte) at a time and I want to use multi-layer encryption (multi-ECC) to increase ...
2
votes
1answer
160 views

Why does the ZUC need an initial vector?

After reading the Specification of the 3GPP Confidentiality and Integrity Algorithms 128-EEA3 & 128-EIA3. Document 2: ZUC Specification, I just cannot figure out why does zuc need an initial ...
2
votes
3answers
121 views

Security of stream cipher with a priori knowledge of message

I am generating a ciphertext by XORing the message bits with key stream bits of a stream cipher. But, if I know a priori that message bits contain a predefined number of 0's (say 60%) at unknown ...
6
votes
1answer
358 views

Why does SpongeWrap not need a Nonce?

The AEAD scheme SpongeWrap based on the sponge construction gets only a header (additional data), a body (the message) and a key as input values, according to the paper where it is defined. What is ...
1
vote
2answers
5k views

What is the difference between a Stream cipher and a Symmetric Encryption algorithm?

According to the Tag definitions: 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 ...
0
votes
1answer
428 views

Difference between a secure PRG and semantically secure encryption

I am taking cryptography course in Coursera from Stanford University. I have following question I have a question why append 0 in G(k) i.e., G'(k) = G(k) || 0 is considered as not secure PRG as 0 in ...
2
votes
3answers
2k views

Using a PRNG for a stream cipher instead of a dedicated algorithm

I am aware, that it is possible to build a stream cipher using some deterministic PRNG (like HASH_DRBG or CTR_DRBG) with good key material as the seed. What are the advantages of using a purpose ...
1
vote
0answers
95 views

How can we efficiently resync a stream cipher

If we have a stream cipher and the key but have lost a significant part of the beginning of the cipher stream of unknown length. Obviously we can add syncing information outside but I was wondering ...
1
vote
1answer
52 views

What is mac-and-continue?

I've seen the term mentioned in a paper by the Keccak team here, and by Adam Langley here when talking about properly authenticating stream ciphers. What does it actually mean, and how does it work? ...
0
votes
1answer
252 views

Are there any authenticated stream ciphers that use the same PRF for MAC and cipher?

A PRF can be used both to generate a key stream for use in a stream cipher, and to construct a MAC to authenticate. The two can then be combined e.g. in a generic encrypt-then-MAC construction to ...
6
votes
2answers
1k views

Why aren't stream ciphers extremely secure?

The way I understand it, stream ciphers are pretty much one time pads off-sourced to a PRNG (the seed is the key that generates the fake one time pad). So why not just use one or more CSPRNGs (...
11
votes
2answers
1k views

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,...
3
votes
1answer
166 views

'Superblock' ciphers?

I'm a noob with very fragmental knowledge of basic crypto. So please excuse me if this question is really stupid. If I understand everything correctly, there are two basic schemes for ciphers: a ...
1
vote
1answer
281 views

Would using two keys for Salsa20 or ChaCha increase security?

Would using the keys (as in two passes with a key each) increase security for Salsa20 or ChaCha stream ciphers increase security?
4
votes
1answer
9k views

How long does a good AES encryption take?

I am encrypting large file sizes (>1GB) using AES encryption with a key size of 256 and over a 1000 hash iterations. To make the program memory efficient I'm reading the file from the stream, chunk by ...
4
votes
1answer
898 views

Fast crytographically secure Pseudo-Random number generator in software

What are the methods for generating pseudo-random numbers in software? I have seen methods where people use SHA implementations from openssl to hash a random message as source of entropy, or using AES ...
3
votes
1answer
335 views

Parameters for comparison of Salsa, HC-128 and SOSEMANUK

I am doing my final project of computer science and I need some help. I understand how Salsa works, but I don't have the same knowledge of HC-128 and SOSEMANUK. I have to do a table with the ...
3
votes
1answer
2k views

Streaming hash function

OK, so we've had questions about hashes build from stream ciphers (not a good idea) and about stream ciphers made out of hashes (yes, of course, use counter mode). What I want to ask is related but ...
1
vote
1answer
436 views

Reuse nonce with Salsa20 stream cipher with counter

It is often said to never use a nonce for more than one message when using a stream cipher. It seems this is to prevent something like this: Taking advantage of one-time pad key reuse? Yet what if I ...
3
votes
1answer
365 views

disadvantages of combination stream and block ciphers

I've encountered some papers online describing ciphers made through a combination of stream and block ciphers. (See this 2008 paper by Sandy Harris: https://eprint.iacr.org/2008/473.pdf) In a ...
3
votes
1answer
440 views

AES in Counter mode for 64 bit input

I was reading how AES can be used for 64 bit data. Than i came to this answer :Is it possible to implement AES with a 64-bit I/O block size? The answer here is given that by running AES in counter ...
0
votes
1answer
176 views

Is the RC4 KSA the same as an extractor?

I am studying the RC4 stream cipher, particularly when it used to be applied in the TLS/SSL protocol. Is it safe to say the KSA acts like an extractor taking in the shared secret key, k (between ...
1
vote
0answers
734 views

Find the initial state of LFSR with n non-consecutive output bits

Let's say I have (e.g.) $32$ output bits of an $128$ bit LFSR whose period length is $2^{128} - 1$. Those output bits are chosen arbitrarily, so I do not have any consecutive bits. Let us call the ...
1
vote
1answer
445 views

How can AES-256-CTR be used to construct a CSPRNG?

I need to generate thousands of random 128-bit IVs per second and would like to amortize calls to /dev/urandom. How can AES-256-CTR be used to construct a CSPRNG? ...
0
votes
1answer
91 views

How secret key is sent in cipher-texts?

Secret key is included in cipher text. so how can we say that if hacker grab the cipher text he will not be able crack the code? if he cannot do with cipher-text then how receiver can crack the ...
2
votes
1answer
2k views

What is insecure about this simple AES implementation?

There are plenty of articles all over the Internet talking about how most people are dangerously bad at crypto, and most people new to the field often fall victim to common pitfalls. I'm new to ...
2
votes
2answers
324 views

Possible to decrypt every fragment of an ecrypted file on its own?

I have a project where I want to encrypt a file and split it up into several fragments and place these files on different systems. I want to do it on mobile phones as well, so I chose poly-chacha20 as ...
5
votes
4answers
392 views

Why are stream ciphers not PRPs?

In a stream cipher like RC4, a message is xored with a random stream of bits, hence a n bits message will result in a n bits random-like ciphertext. So it's a bijection, it's invertible, the output ...
3
votes
2answers
428 views

Are block ciphers more prone to implementation flaws?

I came across a Chrome extension: Minilock It's blog contains a post: "No, the NSA Isn't Breaking AES". Small excerpt is below: A block cipher key is pretty much an initial seed for a pseudo-...
0
votes
1answer
245 views

How to effectively apply combination of Block and Stream Cipher?

I have used TrueCrypt but it uses a cascaded encryption. I want to know about encrypting a file using two ciphers with each cipher having different key. Cipher A (Block Cipher) - with Key KA Cipher ...
6
votes
2answers
7k views

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 ...
3
votes
2answers
175 views

Stream Ciphers — Need clarification on their benefits in practice

Compared to a block cipher which encrypts 16 bytes at a time, stream ciphers can encrypt a byte at a time. I am curious about which applications would immensely benefit from the ability to encrypt a ...
1
vote
1answer
172 views

What's the name of this cipher? And how can it be broken?

Assuming that: SHA-256 and SHA-512 are random and irreversible the output appended to some random and long enough secret is just as random as any other data and will produce values that are just as ...
-2
votes
1answer
700 views

Given alphabetic key and cipher text decrypt the cipher text [closed]

I've been at this for a while. I've been given two things Ciphertext = bsaspp kkuosp Key = rsidpy dkawoa Now seeing the domain that the characters are in. ...
2
votes
1answer
103 views

Reduced variants of stream ciphers

What are "reduced variants" of stream ciphers and how do they relate to lightweight cryptography? How do their internal states compare to those of non-reduced variants? Security aspects?
3
votes
1answer
199 views

Determining strength of a crypto algorithm - clarification with the salsa paper

I am reading through the salsa family paper and on the second page DJB says this -- One can reasonably conjecture, for example, that every function that encrypts data in 0.5 Core-2 cycles/byte is ...
2
votes
1answer
1k views

For CFB, if the IV is corrupted, can the system re-synchronise?

How does CFB (Cipher feedback mode) self correction work? And if the initialization vector (IV) is corrupted during transmission, how will it affect encryption or decryption?
3
votes
3answers
1k views

Finding the probability of a message encrypting to a given ciphertext

I have been watching a crypto course and when they wanted to prove that the OTP is a secure cipher they refer to the probability and what I can't get so far is the understanding of this notation ? $$...

1
3 4
5
6 7
10