Questions tagged [chacha]

ChaCha is a family of stream ciphers proposed by Daniel J. Bernstein, as an evolution of Salsa20 with (conjecturally) improved resistance to cryptanalysis.

Filter by
Sorted by
Tagged with
19
votes
3answers
643 views

Collision or second preimage for the ChaCha core?

Daniel J. Bernstein's ChaCha core is an evolution of the Salsa20 core. Both are functions over the set of 512-bit bitstrings, partitioned as sixteen 32-bit words. Can we exhibit collisions, or second-...
15
votes
2answers
5k views

Why should one prefer Salsa20 over ChaCha?

We are all aware of Google's approach to introduce ChaCha/Poly1305 as TLS cipher suite. The rationale seems clear: ChaCha is newer and seems to provide better security (and maybe speed?) gained from ...
11
votes
3answers
1k views

Why is the core ChaCha primitive not good for use in a CRCF? Why create BLAKE?

Why is the core ChaCha primitive not good for use in a collision-resistant compression function (crypto hash)? Why go through the trouble to create BLAKE? What's wrong with using the core ChaCha ...
10
votes
2answers
2k views

Nonce encryption with Poly1305-Chacha20

I have seen that a couple of companies (like Google, Apple HomeKit) are adding "ChaCha20-Poly1305" as an encryption option. Poly1305 requires algorithm to encrypt the nonce. The Poly1305-AES ...
10
votes
1answer
716 views

Can I use the ChaCha core as a 256-bit to 256-bit one-way function?

I'm looking to implement Lamport signatures as a little fun project, and I need a fast one way function that maps $\{0,1\}^{256} \rightarrow \{0,1\}^{256}$. I was wondering whether I could safely use ...
9
votes
1answer
430 views

Can reduced-round ChaCha be used as non-cryptographic fast PRNG to produce output indistinguishable from random data?

The fastest known attack against the Salsa20 family of stream ciphers requires 2137 simple operations against Salsa20/7, or 2244 against Salsa20/8. The 8-round version encrypts data at 1.88 cycles-per-...
9
votes
1answer
321 views

Why is the whole initial state used in the final addition of Salsa20 and ChaCha?

Both Salsa20 and ChaCha basically work like this: Put the key, the nonce, the sequence number and a constant into a 4x4 matrix of 32-bit words. Transform the matrix invertibly with a number of ARX ...
8
votes
2answers
3k views

Where are the ChaCha20 test vectors/examples?

I see in the Salsa20 specification there are test examples throughout the document to help an implementer make sure every function works as designed. Consequently the whole algorithm would work ...
8
votes
1answer
3k views

Is ChaCha20 safer than AES with respect to side-channel attacks?

I've already seen some topics on this matter, but I feel like my question hasn't really been answered. Given the following: AES must be implemented in hardware (i.e. using the AES-NI instruction set)...
7
votes
0answers
170 views

Why is BLAKE2 faster than chacha20?

Chacha20 is essentially a hash function that maps 512-bit strings to other 512-bit strings which are in turn xored with the plaintext to create the ciphertext. Of the 512-bit input 128-bit are used ...
6
votes
3answers
2k views

Is it safe to use a random numbers instead of a counter in ChaCha20?

Besides the IV, ChaCha20 takes a random number and a counter as input. I couldn't find more precise information about this but it seems to be that the counter is just a safety measure in case of a ...
6
votes
2answers
407 views

Does ChaCha20/Salsa have the same Bit Strength as AES for identical key sizes?

i.e. does ChaCha20 with a 128bit key, require 2^128 attempts to brute force, as with AES-128, theoretically? Ps. notwithstanding that ChaCha is a stream cipher.
6
votes
1answer
2k views

Is ChaCha20 alone sufficient for securing data-at-rest?

I wonder if ChaCha20 alone is sufficient for securing files stored on a disk or should Poly1305 should be used along with it? AFAIK, Poly1305 is used to secure the authentication channel, but for ...
6
votes
1answer
438 views

Does ChaCha20-Poly1305 need random nonce?

RFC 7539 says: A 96-bit nonce -- different for each invocation with the same key It doesn't explicitly say whether it has to be random or not. If we use an ever incrementing counter. Would that be ...
6
votes
1answer
381 views

Would it be safe to use the message hash as the IV in ChaCha?

This seemed like an option if the hash is unpredictable. It could be the hash of the message or the hash of the message + some common secret (apart from the key). The only circumstance in which the ...
6
votes
1answer
1k views

Extending key sizes in Salsa20 and ChaCha?

I've written implementations of Salsa20 and ChaCha that accept 384 and 448 bit keys. It was fairly trivial to implement, the 'sigma' constant is replaced with key material, and the counter, (which was ...
6
votes
1answer
195 views

Reason for 3 rounds ChaCha in ChaCha20Poly1305@openssh

OpenSSH uses a slightly different ChaCha20Poly1305 AEAD construct then the one proposed by A. Langley and others for TLS. The TLS version The openSSH version (and here) The openSSH version uses two ...
6
votes
1answer
212 views

Can NORX32-f be used in a Salsa20 style stream cipher?

#include <std_roll_your_own_crypto_warning.h> With the third round CAESAR candidates about to be announced, the design[0] of Salsa20/ChaCha + Poly1305 is ...
6
votes
3answers
175 views

Mixing x into permutation through XOR vs. modular addition

Block ciphers mix key material into the permutation through XOR. Also do pre and post whitening this way. Chacha/Salsa finishes by 32-bit modular adding key and iv material (among other bits but ...
5
votes
1answer
2k views

What happens if a nonce is reused in ChaCha20-Poly1305?

In ChaCha20-Poly1305, I know that reusing a nonce loses confidentiality and integrity for all messages encrypted with the (key, nonce) pair. However, is security affected for those messages encrypted ...
5
votes
1answer
282 views

In Fortuna, can I use ChaCha20 instead of a block cipher and Blake2b instead of iterated SHA256?

In the Fortuna CSPRNG, can I use ChaCha20 instead of a block cipher and Blake2b instead of double SHA256, and still retain security? My hypothesis is "yes" because: The block cipher's only use is in ...
5
votes
2answers
116 views

Append data to authenticated ciphertext encrypted using a stream cipher

Say we have xSalsa20 authenticated using Poly1305. If $ X $ is the ciphertext, $N$ is the nonce value, and $H$ is the authentication tag such that the final ciphertext is $ N || X || H $, then given ...
5
votes
1answer
830 views

Is ChaCha12 considered 256-bit secure?

ChaCha20 is considered 256-bit secure (no attack faster than brute force). However, the best known cryptanalysis that I know of is on ChaCha7. That gives ChaCha20 a rather large security margin (...
5
votes
1answer
158 views

Latin dance family in block cipher

Is it secure to use Salsa20/ChaCha as the key schedule for a 512-bit block cipher using a public permutation in Even-Mansour construction?
5
votes
1answer
275 views

Can ChaCha be turned into a collision resistant hash function by xoring keystreams?

In his paper about RFSB Bernstein states that the compression function $(m_1,\ m_2,\ m_3,\ ...\ ,\ m_n) \rightarrow c_1[m_1]\ \oplus\ c_2[m_2]\ \oplus c_3[m_3]\ \oplus\ ... \oplus\ c_n[m_n]$ is ...
5
votes
0answers
121 views

Why Salsa20 rotates columns vertically to optimize for SIMD?

I'm writing a school assignment and I'm trying to fully grasp the differences between Salsa20 and ChaCha. I've come to understand that by rotating upwards the initial matrix columns, DJB says that ...
5
votes
0answers
183 views

Can an analog of ChaCha with 64-bit words be defined, and would it be secure? [duplicate]

Blake2b has a lightning fast compression function with more-than-overkill security even against quantum attacks. It seems to be based on ChaCha, but with 64-bit words and different rotation constants....
4
votes
2answers
430 views

Can one extend the nonce of ChaCha/Salsa20 by XORing the extra bits with the key?

Can one extend the ChaCha and Salsa20 nonces by XORing the extra nonce bits with the key? My reasoning is as follows: the Rumba compression function allows attackers to supply any 48-byte input to ...
4
votes
1answer
1k views

Is XChaCha20-Poly1305 nonce misuse-resistant?

In the Libsodium v1.0.12 and v1.0.13 Security Assessment one can read The ChaCha20-Poly1305 implementation combines a stream cipher and is resistant to timing attacks by design. In addition, this ...
4
votes
1answer
371 views

ChaCha20 immune to timing attacks

What are the reasons because of which ChaCha20 is immune to timing attacks ? Also why is not AES immune to timing attacks?
4
votes
3answers
1k views

ChaCha20-Poly1305 test vectors

I was trying to use OpenSSL 1.1 (via Ruby) to validate the ChaCha20-Poly1305 test vector from this IETF draft: https://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-04#section-7 The relevant ...
4
votes
1answer
282 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 ...
4
votes
1answer
543 views

chacha20-poly1305 padding and length encoding

The AEAD construction for chacha20-poly1305 described in the IETF proposal encodes message lengths into the text that is to be hashed. The newer proposal goes further and pads associated data and ...
4
votes
1answer
521 views

Can I reuse a nonce to retransmit the same packet using ChaCha20-Poly1305?

I understand the "sudden death" implications of reusing a nonce with ChaCha20-poly1305, but I believe this rule doesn't apply if you are transmitting exactly the same packet. I'm putting together a ...
4
votes
1answer
511 views

Advantages of HS1-SIV over ChaCha20-Poly1305-SIV?

What advantages does HS1-SIV have over ChaCha20-Poly1305-SIV? I know that both use the ChaCha stream cipher, but I am trying to understand why HS1-Hash is a better MAC. Edit: To hide the Poly1305 ...
4
votes
1answer
112 views

Symmetric encryption algorithms with large IVs and authentication?

Most modern symmetric ciphers require a nonce/IV. If the nonce is reused, security is lost. If the nonce is large enough, it can be generated securely by using a CSPRNG. This avoids needing to keep ...
4
votes
1answer
103 views

Fundamental difference between the constant, key, nonce, and counter bits in Salsa20/ChaCha20 or AES-Encrypt?

The Salsa20 core function takes a 128-bit constant, 256-bit key, 64-bit counter, and 64-bit nonce and produces a 512-bit value. Or more generically, it is a mapping from 512-bit values to 512-bit ...
4
votes
2answers
1k views

Using ChaCha20 as a PRNG with a variable-length seed

As far as I understand, the key stream of the ChaCha20 cipher may be used as a seeded PRNG, where the seed is used to set the key and the nonce. As described in RFC7539, ChaCha20 can be used with a ...
4
votes
1answer
349 views

Where is HChaCha20 formally defined?

I stumbled upon the Q&A “Advantages of HS1-SIV over ChaCha20-Poly1305-SIV?” which mentions “HChaCha20” in the question. Trying to look it up via the usual research sources, I failed to find an ...
4
votes
1answer
639 views

Challenge / Response to Prevent Replay Attack - Using nonce as challenge

I am implementing a radio protocol and trying to prevent replay attacks. It is an embedded system so storing nonce values is not an option, as each node in the system may talk to each other. My plan ...
4
votes
0answers
97 views

Creating an SPN cipher from ChaCha20 or Salsa20's double round function

Given that ChaCha20's building blocks have been also used to construct a hash function, can the double round function from either ChaCha20 or Salsa20 be used to construct a secure SP-network cipher? ...
4
votes
0answers
209 views

How secure is $\operatorname{AES256}_{\operatorname{ECB}}(\operatorname{ChaCha20}(\text{plaintext}))$?

Suppose I encrypt a bytestream using ChaCha20, and then encrypt the resulting ciphertext using AES in ECB mode. How secure is the combination?
3
votes
3answers
368 views

Largest message size for XChaCha20-Poly1305

libsodium documentation says that XChaCha20-Poly1305 can encrypt a message of arbitrary size. However, the only specification available (still a draft) explains that under the hood the IETF version ...
3
votes
1answer
1k views

Does XChaCha20 exist with similar properties to XSalsa20?

Does XChaCha20 (built from ChaCha20 just like XSalsa20 is built from Salsa20) exist and have XSalsa20's desirable properties?
3
votes
1answer
230 views

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 ...
3
votes
1answer
384 views

Can ChaCha20 be repurposed as a general purpose permutation function like Gimli?

I like the idea behind Gimli and libhydrogen but in my benchmarks Gimli permutation function is considerably slower than ChaCha20 one. By considerably I mean four times slower using SIMD builtins. ...
3
votes
1answer
186 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 ...
3
votes
1answer
612 views

384-bit ChaCha20 / Salsa20

The standard Salsa20 core is a $\{0,1\}^{384} \to \{0,1\}^{512}$ random function with a 16 byte constant ($\sigma$ for a 32-byte key), an 8 byte nonce, an 8 byte counter, and a 32 byte key. The hash ...
3
votes
1answer
308 views

Using ChaCha20 on very short messages with high packet loss

I'm building a low power wireless network and need to transmit very small packets at regular intervals (10 bytes every minute or so). In order to secure the communications I'm considering using ...
3
votes
0answers
460 views

Chacha20 random nonce + counter

I need to establish potentially infinite secure streams of data between many remote devices with very few resources. Chacha20 is lightweight enough, but I do not trust myself to implement a reliable ...