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refactor: Refactor Keccak256Transcript and update tests (#191)
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* refactor: change the order of Keccak Squeeze's input

- Redefine the input sequence for the `compute_updated_state` within the `squeeze` method in `Keccak256Transcript`.
- Modify the expected hash outcomes in the `test_keccak_transcript_with` function in `keccak.rs`.

* refactor: Refactor Keccak256Transcript

- Replaced the transcript vector with a `Keccak256` instance, improving data handling and memory usage.
- Refactored `compute_updated_state` to work directly on a given `Keccak256` instance, reducing unnecessary object creation.
- this change roughly amounts to putting the transcript at the start of squeeze's input array

* refactor: simplify hasher_lo, hasher_hi

* test: Enhance Keccak transcript with backward compatibility test

- Introduces new helper functions to assist with the backward-compatibility intesting process (`compute_updated_state_for_testing`, `squeeze_for_testing`)
- Adds a new test `test_keccak_transcript_incremental_vs_explicit` that checks for consistency between incremental and independent explicit transcript computations
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@huitseeker
huitseeker authored Jul 6, 2023
1 parent 4b077bc commit 0664244
Showing 1 changed file with 111 additions and 22 deletions.
133 changes: 111 additions & 22 deletions src/provider/keccak.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,19 +18,22 @@ const KECCAK256_PREFIX_CHALLENGE_HI: u8 = 1;
pub struct Keccak256Transcript<G: Group> {
round: u16,
state: [u8; KECCAK256_STATE_SIZE],
transcript: Vec<u8>,
transcript: Keccak256,
_p: PhantomData<G>,
}

fn compute_updated_state(input: &[u8]) -> [u8; KECCAK256_STATE_SIZE] {
let input_lo = [input, &[KECCAK256_PREFIX_CHALLENGE_LO]].concat();
let input_hi = [input, &[KECCAK256_PREFIX_CHALLENGE_HI]].concat();
fn compute_updated_state(keccak_instance: Keccak256, input: &[u8]) -> [u8; KECCAK256_STATE_SIZE] {
let mut updated_instance = keccak_instance;
updated_instance.input(input);

let mut hasher_lo = Keccak256::new();
let mut hasher_hi = Keccak256::new();
let input_lo = &[KECCAK256_PREFIX_CHALLENGE_LO];
let input_hi = &[KECCAK256_PREFIX_CHALLENGE_HI];

hasher_lo.input(&input_lo);
hasher_hi.input(&input_hi);
let mut hasher_lo = updated_instance.clone();
let mut hasher_hi = updated_instance;

hasher_lo.input(input_lo);
hasher_hi.input(input_hi);

let output_lo = hasher_lo.result();
let output_hi = hasher_hi.result();
Expand All @@ -44,27 +47,28 @@ fn compute_updated_state(input: &[u8]) -> [u8; KECCAK256_STATE_SIZE] {

impl<G: Group> TranscriptEngineTrait<G> for Keccak256Transcript<G> {
fn new(label: &'static [u8]) -> Self {
let keccak_instance = Keccak256::new();
let input = [PERSONA_TAG, label].concat();
let output = compute_updated_state(&input);
let output = compute_updated_state(keccak_instance.clone(), &input);

Self {
round: 0u16,
state: output,
transcript: vec![],
transcript: keccak_instance,
_p: Default::default(),
}
}

fn squeeze(&mut self, label: &'static [u8]) -> Result<G::Scalar, NovaError> {
// we gather the full input from the round, preceded by the current state of the transcript
let input = [
DOM_SEP_TAG,
self.round.to_le_bytes().as_ref(),
self.state.as_ref(),
self.transcript.as_ref(),
label,
]
.concat();
let output = compute_updated_state(&input);
let output = compute_updated_state(self.transcript.clone(), &input);

// update state
self.round = {
Expand All @@ -75,20 +79,20 @@ impl<G: Group> TranscriptEngineTrait<G> for Keccak256Transcript<G> {
}
};
self.state.copy_from_slice(&output);
self.transcript = vec![];
self.transcript = Keccak256::new();

// squeeze out a challenge
Ok(G::Scalar::from_uniform(&output))
}

fn absorb<T: TranscriptReprTrait<G>>(&mut self, label: &'static [u8], o: &T) {
self.transcript.extend_from_slice(label);
self.transcript.extend_from_slice(&o.to_transcript_bytes());
self.transcript.input(label);
self.transcript.input(&o.to_transcript_bytes());
}

fn dom_sep(&mut self, bytes: &'static [u8]) {
self.transcript.extend_from_slice(DOM_SEP_TAG);
self.transcript.extend_from_slice(bytes);
self.transcript.input(DOM_SEP_TAG);
self.transcript.input(bytes);
}
}

Expand All @@ -97,9 +101,10 @@ mod tests {
use crate::{
provider::bn256_grumpkin::bn256,
provider::keccak::Keccak256Transcript,
traits::{Group, TranscriptEngineTrait},
traits::{Group, PrimeFieldExt, TranscriptEngineTrait, TranscriptReprTrait},
};
use ff::PrimeField;
use rand::Rng;
use sha3::{Digest, Keccak256};

fn test_keccak_transcript_with<G: Group>(expected_h1: &'static str, expected_h2: &'static str) {
Expand Down Expand Up @@ -131,13 +136,13 @@ mod tests {
#[test]
fn test_keccak_transcript() {
test_keccak_transcript_with::<pasta_curves::pallas::Point>(
"432d5811c8be3d44d47f52108a8749ae18482efd1a37b830f966456b5d75340c",
"65f7908d53abcd18f3b1d767456ef9009b91c7566a635e9ca7be26e21d4d7a10",
"5ddffa8dc091862132788b8976af88b9a2c70594727e611c7217ba4c30c8c70a",
"4d4bf42c065870395749fa1c4fb641df1e0d53f05309b03d5b1db7f0be3aa13d",
);

test_keccak_transcript_with::<bn256::Point>(
"93f9160d5501865b399ee4ff0ffe17b697a4023e33e931e2597d36e6cc4ac602",
"bca8bdb96608a8277a7cb34bd493dfbc5baf2a080d1d6c9d32d7ab4f238eb803",
"9fb71e3b74bfd0b60d97349849b895595779a240b92a6fae86bd2812692b6b0e",
"bfd4c50b7d6317e9267d5d65c985eb455a3561129c0b3beef79bfc8461a84f18",
);
}

Expand All @@ -151,4 +156,88 @@ mod tests {
"29045a592007d0c246ef02c2223570da9522d0cf0f73282c79a1bc8f0bb2c238"
);
}

use super::{
DOM_SEP_TAG, KECCAK256_PREFIX_CHALLENGE_HI, KECCAK256_PREFIX_CHALLENGE_LO,
KECCAK256_STATE_SIZE, PERSONA_TAG,
};

fn compute_updated_state_for_testing(input: &[u8]) -> [u8; KECCAK256_STATE_SIZE] {
let input_lo = [input, &[KECCAK256_PREFIX_CHALLENGE_LO]].concat();
let input_hi = [input, &[KECCAK256_PREFIX_CHALLENGE_HI]].concat();

let mut hasher_lo = Keccak256::new();
let mut hasher_hi = Keccak256::new();

hasher_lo.input(&input_lo);
hasher_hi.input(&input_hi);

let output_lo = hasher_lo.result();
let output_hi = hasher_hi.result();

[output_lo, output_hi]
.concat()
.as_slice()
.try_into()
.unwrap()
}

fn squeeze_for_testing(
transcript: &[u8],
round: u16,
state: [u8; KECCAK256_STATE_SIZE],
label: &'static [u8],
) -> [u8; 64] {
let input = [
transcript,
DOM_SEP_TAG,
round.to_le_bytes().as_ref(),
state.as_ref(),
label,
]
.concat();
compute_updated_state_for_testing(&input)
}

// This test is meant to ensure compatibility between the incremental way of computing the transcript above, and
// the former, which materialized the entirety of the input vector before calling Keccak256 on it.
fn test_keccak_transcript_incremental_vs_explicit_with<G: Group>() {
let test_label = b"test";
let mut transcript: Keccak256Transcript<G> = Keccak256Transcript::new(test_label);
let mut rng = rand::thread_rng();

// ten scalars
let scalars = std::iter::from_fn(|| Some(<G as Group>::Scalar::from(rng.gen::<u64>())))
.take(10)
.collect::<Vec<_>>();

// add the scalars to the transcripts,
let mut manual_transcript: Vec<u8> = vec![];
let labels = vec![
b"s1", b"s2", b"s3", b"s4", b"s5", b"s6", b"s7", b"s8", b"s9", b"s0",
];

for i in 0..10 {
transcript.absorb(&labels[i][..], &scalars[i]);
manual_transcript.extend(labels[i]);
manual_transcript.extend(scalars[i].to_transcript_bytes());
}

// compute the initial state
let input = [PERSONA_TAG, test_label].concat();
let initial_state = compute_updated_state_for_testing(&input);

// make a challenge
let c1: <G as Group>::Scalar = transcript.squeeze(b"c1").unwrap();

let c1_bytes = squeeze_for_testing(&manual_transcript[..], 0u16, initial_state, b"c1");
let to_hex = |g: G::Scalar| hex::encode(g.to_repr().as_ref());
assert_eq!(to_hex(c1), to_hex(G::Scalar::from_uniform(&c1_bytes)));
}

#[test]
fn test_keccak_transcript_incremental_vs_explicit() {
test_keccak_transcript_incremental_vs_explicit_with::<pasta_curves::pallas::Point>();
test_keccak_transcript_incremental_vs_explicit_with::<bn256::Point>();
}
}

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