Batch match and multiscalar multiplication for redpallas

Resolves #2098
This commit is contained in:
Deirdre Connolly 2021-06-12 03:11:44 -04:00
parent b59121b09e
commit d5687720c2
7 changed files with 674 additions and 0 deletions

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@ -76,3 +76,7 @@ zebra-test = { path = "../zebra-test/" }
[[bench]]
name = "block"
harness = false
[[bench]]
name = "redpallas"
harness = false

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@ -0,0 +1,96 @@
use std::convert::TryFrom;
use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion, Throughput};
use rand::{thread_rng, Rng};
use zebra_chain::primitives::redpallas::*;
enum Item {
SpendAuth {
vk_bytes: VerificationKeyBytes<SpendAuth>,
sig: Signature<SpendAuth>,
},
Binding {
vk_bytes: VerificationKeyBytes<Binding>,
sig: Signature<Binding>,
},
}
fn sigs_with_distinct_keys() -> impl Iterator<Item = Item> {
std::iter::repeat_with(|| {
let mut rng = thread_rng();
let msg = b"";
match rng.gen::<u8>() % 2 {
0 => {
let sk = SigningKey::<SpendAuth>::new(thread_rng());
let vk_bytes = VerificationKey::from(&sk).into();
let sig = sk.sign(thread_rng(), &msg[..]);
Item::SpendAuth { vk_bytes, sig }
}
1 => {
let sk = SigningKey::<Binding>::new(thread_rng());
let vk_bytes = VerificationKey::from(&sk).into();
let sig = sk.sign(thread_rng(), &msg[..]);
Item::Binding { vk_bytes, sig }
}
_ => panic!(),
}
})
}
fn bench_batch_verify(c: &mut Criterion) {
let mut group = c.benchmark_group("Batch Verification");
for &n in [8usize, 16, 24, 32, 40, 48, 56, 64].iter() {
group.throughput(Throughput::Elements(n as u64));
let sigs = sigs_with_distinct_keys().take(n).collect::<Vec<_>>();
group.bench_with_input(
BenchmarkId::new("Unbatched verification", n),
&sigs,
|b, sigs| {
b.iter(|| {
for item in sigs.iter() {
let msg = b"Bench";
match item {
Item::SpendAuth { vk_bytes, sig } => {
let _ = VerificationKey::try_from(*vk_bytes)
.and_then(|vk| vk.verify(msg, sig));
}
Item::Binding { vk_bytes, sig } => {
let _ = VerificationKey::try_from(*vk_bytes)
.and_then(|vk| vk.verify(msg, sig));
}
}
}
})
},
);
group.bench_with_input(
BenchmarkId::new("Batched verification", n),
&sigs,
|b, sigs| {
b.iter(|| {
let mut batch = batch::Verifier::new();
for item in sigs.iter() {
let msg = b"Bench";
match item {
Item::SpendAuth { vk_bytes, sig } => {
batch.queue((*vk_bytes, *sig, msg));
}
Item::Binding { vk_bytes, sig } => {
batch.queue((*vk_bytes, *sig, msg));
}
}
}
batch.verify(thread_rng())
})
},
);
}
group.finish();
}
criterion_group!(benches, bench_batch_verify);
criterion_main!(benches);

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@ -13,10 +13,12 @@
use group::GroupEncoding;
use halo2::pasta::pallas;
pub mod batch;
mod constants;
#[allow(missing_docs)]
mod error;
mod hash;
mod scalar_mul;
mod signature;
mod signing_key;
#[cfg(test)]

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@ -0,0 +1,265 @@
// -*- mode: rust; -*-
//
// This file is part of redpallas.
// Copyright (c) 2019-2021 Zcash Foundation
// See LICENSE for licensing information.
//
// Authors:
// - Deirdre Connolly <deirdre@zfnd.org>
// - Henry de Valence <hdevalence@hdevalence.ca>
//! Performs batch RedPallas signature verification.
//!
//! Batch verification asks whether *all* signatures in some set are valid,
//! rather than asking whether *each* of them is valid. This allows sharing
//! computations among all signature verifications, performing less work overall
//! at the cost of higher latency (the entire batch must complete), complexity of
//! caller code (which must assemble a batch of signatures across work-items),
//! and loss of the ability to easily pinpoint failing signatures.
//!
use std::convert::TryFrom;
use group::{Group, GroupEncoding};
use halo2::arithmetic::FieldExt;
use rand_core::{CryptoRng, RngCore};
use super::{private::Sealed, scalar_mul::VartimeMultiscalarMul, *};
// Shim to generate a random 128bit value in a [u64; 4], without
// importing `rand`.
fn gen_128_bits<R: RngCore + CryptoRng>(mut rng: R) -> [u64; 4] {
let mut bytes = [0u64; 4];
bytes[0] = rng.next_u64();
bytes[1] = rng.next_u64();
bytes
}
#[derive(Clone, Debug)]
enum Inner {
SpendAuth {
vk_bytes: VerificationKeyBytes<SpendAuth>,
sig: Signature<SpendAuth>,
c: pallas::Scalar,
},
Binding {
vk_bytes: VerificationKeyBytes<Binding>,
sig: Signature<Binding>,
c: pallas::Scalar,
},
}
/// A batch verification item.
///
/// This struct exists to allow batch processing to be decoupled from the
/// lifetime of the message. This is useful when using the batch verification API
/// in an async context.
#[derive(Clone, Debug)]
pub struct Item {
inner: Inner,
}
impl<'msg, M: AsRef<[u8]>>
From<(
VerificationKeyBytes<SpendAuth>,
Signature<SpendAuth>,
&'msg M,
)> for Item
{
fn from(
(vk_bytes, sig, msg): (
VerificationKeyBytes<SpendAuth>,
Signature<SpendAuth>,
&'msg M,
),
) -> Self {
// Compute c now to avoid dependency on the msg lifetime.
let c = HStar::default()
.update(&sig.r_bytes[..])
.update(&vk_bytes.bytes[..])
.update(msg)
.finalize();
Self {
inner: Inner::SpendAuth { vk_bytes, sig, c },
}
}
}
impl<'msg, M: AsRef<[u8]>> From<(VerificationKeyBytes<Binding>, Signature<Binding>, &'msg M)>
for Item
{
fn from(
(vk_bytes, sig, msg): (VerificationKeyBytes<Binding>, Signature<Binding>, &'msg M),
) -> Self {
// Compute c now to avoid dependency on the msg lifetime.
let c = HStar::default()
.update(&sig.r_bytes[..])
.update(&vk_bytes.bytes[..])
.update(msg)
.finalize();
Self {
inner: Inner::Binding { vk_bytes, sig, c },
}
}
}
impl Item {
/// Perform non-batched verification of this `Item`.
///
/// This is useful (in combination with `Item::clone`) for implementing fallback
/// logic when batch verification fails. In contrast to
/// [`VerificationKey::verify`](crate::VerificationKey::verify), which requires
/// borrowing the message data, the `Item` type is unlinked from the lifetime of
/// the message.
#[allow(non_snake_case)]
pub fn verify_single(self) -> Result<(), Error> {
match self.inner {
Inner::Binding { vk_bytes, sig, c } => VerificationKey::<Binding>::try_from(vk_bytes)
.and_then(|vk| vk.verify_prehashed(&sig, c)),
Inner::SpendAuth { vk_bytes, sig, c } => {
VerificationKey::<SpendAuth>::try_from(vk_bytes)
.and_then(|vk| vk.verify_prehashed(&sig, c))
}
}
}
}
#[derive(Default)]
/// A batch verification context.
pub struct Verifier {
/// Signature data queued for verification.
signatures: Vec<Item>,
}
impl Verifier {
/// Construct a new batch verifier.
pub fn new() -> Verifier {
Verifier::default()
}
/// Queue an Item for verification.
pub fn queue<I: Into<Item>>(&mut self, item: I) {
self.signatures.push(item.into());
}
/// Perform batch verification, returning `Ok(())` if all signatures were
/// valid and `Err` otherwise.
///
/// The batch verification equation is:
///
/// h_G * -[sum(z_i * s_i)]P_G + sum(\[z_i\]R_i + [z_i * c_i]VK_i) = 0_G
///
/// which we split out into:
///
/// h_G * -[sum(z_i * s_i)]P_G + sum(\[z_i\]R_i) + sum([z_i * c_i]VK_i) = 0_G
///
/// so that we can use multiscalar multiplication speedups.
///
/// where for each signature i,
/// - VK_i is the verification key;
/// - R_i is the signature's R value;
/// - s_i is the signature's s value;
/// - c_i is the hash of the message and other data;
/// - z_i is a random 128-bit Scalar;
/// - h_G is the cofactor of the group;
/// - P_G is the generator of the subgroup;
///
/// Since RedPallas uses different subgroups for different types
/// of signatures, SpendAuth's and Binding's, we need to have yet
/// another point and associated scalar accumulator for all the
/// signatures of each type in our batch, but we can still
/// amortize computation nicely in one multiscalar multiplication:
///
/// h_G * ( [-sum(z_i * s_i): i_type == SpendAuth]P_SpendAuth + [-sum(z_i * s_i): i_type == Binding]P_Binding + sum(\[z_i\]R_i) + sum([z_i * c_i]VK_i) ) = 0_G
///
/// As follows elliptic curve scalar multiplication convention,
/// scalar variables are lowercase and group point variables
/// are uppercase. This does not exactly match the RedDSA
/// notation in the [protocol specification §B.1][ps].
///
/// [ps]: https://zips.z.cash/protocol/protocol.pdf#reddsabatchverify
#[allow(non_snake_case)]
pub fn verify<R: RngCore + CryptoRng>(self, mut rng: R) -> Result<(), Error> {
let n = self.signatures.len();
let mut VK_coeffs = Vec::with_capacity(n);
let mut VKs = Vec::with_capacity(n);
let mut R_coeffs = Vec::with_capacity(self.signatures.len());
let mut Rs = Vec::with_capacity(self.signatures.len());
let mut P_spendauth_coeff = pallas::Scalar::zero();
let mut P_binding_coeff = pallas::Scalar::zero();
for item in self.signatures.iter() {
let (s_bytes, r_bytes, c) = match item.inner {
Inner::SpendAuth { sig, c, .. } => (sig.s_bytes, sig.r_bytes, c),
Inner::Binding { sig, c, .. } => (sig.s_bytes, sig.r_bytes, c),
};
let s = {
// XXX-pallas: should not use CtOption here
let maybe_scalar = pallas::Scalar::from_bytes(&s_bytes);
if maybe_scalar.is_some().into() {
maybe_scalar.unwrap()
} else {
return Err(Error::InvalidSignature);
}
};
let R = {
// XXX-pallas: should not use CtOption here
// XXX-pallas: inconsistent ownership in from_bytes
let maybe_point = pallas::Affine::from_bytes(&r_bytes);
if maybe_point.is_some().into() {
pallas::Point::from(maybe_point.unwrap())
} else {
return Err(Error::InvalidSignature);
}
};
let VK = match item.inner {
Inner::SpendAuth { vk_bytes, .. } => {
VerificationKey::<SpendAuth>::try_from(vk_bytes.bytes)?.point
}
Inner::Binding { vk_bytes, .. } => {
VerificationKey::<Binding>::try_from(vk_bytes.bytes)?.point
}
};
let z = pallas::Scalar::from_raw(gen_128_bits(&mut rng));
let P_coeff = z * s;
match item.inner {
Inner::SpendAuth { .. } => {
P_spendauth_coeff -= P_coeff;
}
Inner::Binding { .. } => {
P_binding_coeff -= P_coeff;
}
};
R_coeffs.push(z);
Rs.push(R);
VK_coeffs.push(pallas::Scalar::zero() + (z * c));
VKs.push(VK);
}
use std::iter::once;
let scalars = once(&P_spendauth_coeff)
.chain(once(&P_binding_coeff))
.chain(VK_coeffs.iter())
.chain(R_coeffs.iter());
let basepoints = [SpendAuth::basepoint(), Binding::basepoint()];
let points = basepoints.iter().chain(VKs.iter()).chain(Rs.iter());
let check = pallas::Point::vartime_multiscalar_mul(scalars, points);
if check.is_identity().into() {
Ok(())
} else {
Err(Error::InvalidSignature)
}
}
}

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@ -0,0 +1,207 @@
// -*- mode: rust; -*-
//
// This file is part of redpallas.
// Copyright (c) 2019-2021 Zcash Foundation
// Copyright (c) 2017-2021 isis agora lovecruft, Henry de Valence
// See LICENSE for licensing information.
//
// Authors:
// - isis agora lovecruft <isis@patternsinthevoid.net>
// - Henry de Valence <hdevalence@hdevalence.ca>
// - Deirdre Connolly <deirdre@zfnd.org>
use std::{borrow::Borrow, fmt::Debug};
use group::Group;
use halo2::{arithmetic::FieldExt, pasta::pallas};
pub trait NonAdjacentForm {
fn non_adjacent_form(&self, w: usize) -> [i8; 256];
}
/// A trait for variable-time multiscalar multiplication without precomputation.
pub trait VartimeMultiscalarMul {
/// The type of point being multiplied, e.g., `AffinePoint`.
type Point;
/// Given an iterator of public scalars and an iterator of
/// `Option`s of points, compute either `Some(Q)`, where
/// $$
/// Q = c\_1 P\_1 + \cdots + c\_n P\_n,
/// $$
/// if all points were `Some(P_i)`, or else return `None`.
fn optional_multiscalar_mul<I, J>(scalars: I, points: J) -> Option<Self::Point>
where
I: IntoIterator,
I::Item: Borrow<pallas::Scalar>,
J: IntoIterator<Item = Option<Self::Point>>;
/// Given an iterator of public scalars and an iterator of
/// public points, compute
/// $$
/// Q = c\_1 P\_1 + \cdots + c\_n P\_n,
/// $$
/// using variable-time operations.
///
/// It is an error to call this function with two iterators of different lengths.
fn vartime_multiscalar_mul<I, J>(scalars: I, points: J) -> Self::Point
where
I: IntoIterator,
I::Item: Borrow<pallas::Scalar>,
J: IntoIterator,
J::Item: Borrow<Self::Point>,
Self::Point: Clone,
{
Self::optional_multiscalar_mul(
scalars,
points.into_iter().map(|p| Some(p.borrow().clone())),
)
.unwrap()
}
}
impl NonAdjacentForm for pallas::Scalar {
/// Compute a width-\\(w\\) "Non-Adjacent Form" of this scalar.
///
/// Thanks to curve25519-dalek
fn non_adjacent_form(&self, w: usize) -> [i8; 256] {
// required by the NAF definition
debug_assert!(w >= 2);
// required so that the NAF digits fit in i8
debug_assert!(w <= 8);
use byteorder::{ByteOrder, LittleEndian};
let mut naf = [0i8; 256];
let mut x_u64 = [0u64; 5];
LittleEndian::read_u64_into(&self.to_bytes(), &mut x_u64[0..4]);
let width = 1 << w;
let window_mask = width - 1;
let mut pos = 0;
let mut carry = 0;
while pos < 256 {
// Construct a buffer of bits of the scalar, starting at bit `pos`
let u64_idx = pos / 64;
let bit_idx = pos % 64;
let bit_buf: u64;
if bit_idx < 64 - w {
// This window's bits are contained in a single u64
bit_buf = x_u64[u64_idx] >> bit_idx;
} else {
// Combine the current u64's bits with the bits from the next u64
bit_buf = (x_u64[u64_idx] >> bit_idx) | (x_u64[1 + u64_idx] << (64 - bit_idx));
}
// Add the carry into the current window
let window = carry + (bit_buf & window_mask);
if window & 1 == 0 {
// If the window value is even, preserve the carry and continue.
// Why is the carry preserved?
// If carry == 0 and window & 1 == 0, then the next carry should be 0
// If carry == 1 and window & 1 == 0, then bit_buf & 1 == 1 so the next carry should be 1
pos += 1;
continue;
}
if window < width / 2 {
carry = 0;
naf[pos] = window as i8;
} else {
carry = 1;
naf[pos] = (window as i8).wrapping_sub(width as i8);
}
pos += w;
}
naf
}
}
/// Holds odd multiples 1A, 3A, ..., 15A of a point A.
#[derive(Copy, Clone)]
pub(crate) struct LookupTable5<T>(pub(crate) [T; 8]);
impl<T: Copy> LookupTable5<T> {
/// Given public, odd \\( x \\) with \\( 0 < x < 2^4 \\), return \\(xA\\).
pub fn select(&self, x: usize) -> T {
debug_assert_eq!(x & 1, 1);
debug_assert!(x < 16);
self.0[x / 2]
}
}
impl<T: Debug> Debug for LookupTable5<T> {
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
write!(f, "LookupTable5({:?})", self.0)
}
}
impl<'a> From<&'a pallas::Point> for LookupTable5<pallas::Point> {
#[allow(non_snake_case)]
fn from(A: &'a pallas::Point) -> Self {
let mut Ai = [*A; 8];
let A2 = A.double();
for i in 0..7 {
Ai[i + 1] = A2 + Ai[i];
}
// Now Ai = [A, 3A, 5A, 7A, 9A, 11A, 13A, 15A]
LookupTable5(Ai)
}
}
impl VartimeMultiscalarMul for pallas::Point {
type Point = pallas::Point;
/// Variable-time multiscalar multiplication using a non-adjacent form of
/// width (5).
///
/// The non-adjacent form has signed, odd digits. Using only odd digits
/// halves the table size (since we only need odd multiples), or gives fewer
/// additions for the same table size.
///
/// As the name implies, the runtime varies according to the values of the
/// inputs, thus is not safe for computing over secret data, but is great
/// for computing over public data, such as validating signatures.
#[allow(non_snake_case)]
#[allow(clippy::comparison_chain)]
fn optional_multiscalar_mul<I, J>(scalars: I, points: J) -> Option<pallas::Point>
where
I: IntoIterator,
I::Item: Borrow<pallas::Scalar>,
J: IntoIterator<Item = Option<pallas::Point>>,
{
let nafs: Vec<_> = scalars
.into_iter()
.map(|c| c.borrow().non_adjacent_form(5))
.collect();
let lookup_tables = points
.into_iter()
.map(|P_opt| P_opt.map(|P| LookupTable5::<pallas::Point>::from(&P)))
.collect::<Option<Vec<_>>>()?;
let mut r = pallas::Point::identity();
for i in (0..256).rev() {
let mut t = r.double();
for (naf, lookup_table) in nafs.iter().zip(lookup_tables.iter()) {
if naf[i] > 0 {
t += lookup_table.select(naf[i] as usize);
} else if naf[i] < 0 {
t -= lookup_table.select(-naf[i] as usize);
}
}
r = t;
}
Some(r)
}
}

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@ -1,2 +1,3 @@
mod basepoints;
mod batch;
mod prop;

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@ -0,0 +1,99 @@
use rand::thread_rng;
use super::super::*;
#[test]
fn spendauth_batch_verify() {
let mut rng = thread_rng();
let mut batch = batch::Verifier::new();
for _ in 0..32 {
let sk = SigningKey::<SpendAuth>::new(&mut rng);
let vk = VerificationKey::from(&sk);
let msg = b"BatchVerifyTest";
let sig = sk.sign(&mut rng, &msg[..]);
batch.queue((vk.into(), sig, msg));
}
assert!(batch.verify(rng).is_ok());
}
#[test]
fn binding_batch_verify() {
let mut rng = thread_rng();
let mut batch = batch::Verifier::new();
for _ in 0..32 {
let sk = SigningKey::<Binding>::new(&mut rng);
let vk = VerificationKey::from(&sk);
let msg = b"BatchVerifyTest";
let sig = sk.sign(&mut rng, &msg[..]);
batch.queue((vk.into(), sig, msg));
}
assert!(batch.verify(rng).is_ok());
}
#[test]
fn alternating_batch_verify() {
let mut rng = thread_rng();
let mut batch = batch::Verifier::new();
for i in 0..32 {
let item: batch::Item = match i % 2 {
0 => {
let sk = SigningKey::<SpendAuth>::new(&mut rng);
let vk = VerificationKey::from(&sk);
let msg = b"BatchVerifyTest";
let sig = sk.sign(&mut rng, &msg[..]);
(vk.into(), sig, msg).into()
}
1 => {
let sk = SigningKey::<Binding>::new(&mut rng);
let vk = VerificationKey::from(&sk);
let msg = b"BatchVerifyTest";
let sig = sk.sign(&mut rng, &msg[..]);
(vk.into(), sig, msg).into()
}
_ => unreachable!(),
};
batch.queue(item);
}
assert!(batch.verify(rng).is_ok());
}
#[test]
fn bad_batch_verify() {
let mut rng = thread_rng();
let bad_index = 4; // must be even
let mut batch = batch::Verifier::new();
let mut items = Vec::new();
for i in 0..32 {
let item: batch::Item = match i % 2 {
0 => {
let sk = SigningKey::<SpendAuth>::new(&mut rng);
let vk = VerificationKey::from(&sk);
let msg = b"BatchVerifyTest";
let sig = if i != bad_index {
sk.sign(&mut rng, &msg[..])
} else {
sk.sign(&mut rng, b"bad")
};
(vk.into(), sig, msg).into()
}
1 => {
let sk = SigningKey::<Binding>::new(&mut rng);
let vk = VerificationKey::from(&sk);
let msg = b"BatchVerifyTest";
let sig = sk.sign(&mut rng, &msg[..]);
(vk.into(), sig, msg).into()
}
_ => unreachable!(),
};
items.push(item.clone());
batch.queue(item);
}
assert!(batch.verify(rng).is_err());
for (i, item) in items.drain(..).enumerate() {
if i != bad_index {
assert!(item.verify_single().is_ok());
} else {
assert!(item.verify_single().is_err());
}
}
}