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https://github.com/hinto-janai/cuprate.git
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storage: Add common amounts commitment lookup table (#323)
Add common ammounts commitment lookup table - Implements `compute_zero_commitment` function in `cuprate-helper::crypto` module. - Added test that compare the function output with the correct calculation. - Use of a constant-time algorithm for the lookup table. - Added according documentation
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SyntheticBird
GitHub
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7 changed files with 142 additions and 19 deletions
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@ -19,4 +19,4 @@ rpc = []
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[dev-dependencies]
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[lints]
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workspace = true
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workspace = true
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@ -16,6 +16,7 @@ atomic = ["dep:crossbeam"]
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asynch = ["dep:futures", "dep:rayon"]
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cast = []
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constants = []
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crypto = ["dep:curve25519-dalek", "dep:monero-serai", "std"]
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fs = ["dep:dirs"]
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num = []
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map = ["cast", "dep:monero-serai", "dep:cuprate-constants"]
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@ -26,12 +27,13 @@ tx = ["dep:monero-serai"]
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[dependencies]
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cuprate-constants = { path = "../constants", optional = true, features = ["block"] }
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crossbeam = { workspace = true, optional = true }
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chrono = { workspace = true, optional = true, features = ["std", "clock"] }
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dirs = { workspace = true, optional = true }
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futures = { workspace = true, optional = true, features = ["std"] }
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monero-serai = { workspace = true, optional = true }
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rayon = { workspace = true, optional = true }
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chrono = { workspace = true, optional = true, features = ["std", "clock"] }
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crossbeam = { workspace = true, optional = true }
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curve25519-dalek = { workspace = true, optional = true }
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dirs = { workspace = true, optional = true }
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futures = { workspace = true, optional = true, features = ["std"] }
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monero-serai = { workspace = true, optional = true }
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rayon = { workspace = true, optional = true }
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# This is kinda a stupid work around.
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# [thread] needs to activate one of these libs (windows|libc)
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122
helper/src/crypto.rs
Normal file
122
helper/src/crypto.rs
Normal file
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@ -0,0 +1,122 @@
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//! Crypto related functions and runtime initialized constants
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//---------------------------------------------------------------------------------------------------- Use
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use std::sync::LazyLock;
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use curve25519_dalek::{
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constants::ED25519_BASEPOINT_POINT, edwards::VartimeEdwardsPrecomputation,
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traits::VartimePrecomputedMultiscalarMul, EdwardsPoint, Scalar,
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};
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use monero_serai::generators::H;
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//---------------------------------------------------------------------------------------------------- Pre-computation
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/// This is the decomposed amount table containing the mandatory Pre-RCT amounts. It is used to pre-compute
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/// zero commitments at runtime.
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///
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/// Defined at:
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/// - <https://github.com/monero-project/monero/blob/893916ad091a92e765ce3241b94e706ad012b62a/src/ringct/rctOps.cpp#L44>
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#[rustfmt::skip]
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pub const ZERO_COMMITMENT_DECOMPOSED_AMOUNT: [u64; 172] = [
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1, 2, 3, 4, 5, 6, 7, 8, 9,
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10, 20, 30, 40, 50, 60, 70, 80, 90,
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100, 200, 300, 400, 500, 600, 700, 800, 900,
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1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000,
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10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000,
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100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000,
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1000000, 2000000, 3000000, 4000000, 5000000, 6000000, 7000000, 8000000, 9000000,
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10000000, 20000000, 30000000, 40000000, 50000000, 60000000, 70000000, 80000000, 90000000,
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100000000, 200000000, 300000000, 400000000, 500000000, 600000000, 700000000, 800000000, 900000000,
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1000000000, 2000000000, 3000000000, 4000000000, 5000000000, 6000000000, 7000000000, 8000000000, 9000000000,
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10000000000, 20000000000, 30000000000, 40000000000, 50000000000, 60000000000, 70000000000, 80000000000, 90000000000,
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100000000000, 200000000000, 300000000000, 400000000000, 500000000000, 600000000000, 700000000000, 800000000000, 900000000000,
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1000000000000, 2000000000000, 3000000000000, 4000000000000, 5000000000000, 6000000000000, 7000000000000, 8000000000000, 9000000000000,
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10000000000000, 20000000000000, 30000000000000, 40000000000000, 50000000000000, 60000000000000, 70000000000000, 80000000000000, 90000000000000,
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100000000000000, 200000000000000, 300000000000000, 400000000000000, 500000000000000, 600000000000000, 700000000000000, 800000000000000, 900000000000000,
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1000000000000000, 2000000000000000, 3000000000000000, 4000000000000000, 5000000000000000, 6000000000000000, 7000000000000000, 8000000000000000, 9000000000000000,
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10000000000000000, 20000000000000000, 30000000000000000, 40000000000000000, 50000000000000000, 60000000000000000, 70000000000000000, 80000000000000000, 90000000000000000,
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100000000000000000, 200000000000000000, 300000000000000000, 400000000000000000, 500000000000000000, 600000000000000000, 700000000000000000, 800000000000000000, 900000000000000000,
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1000000000000000000, 2000000000000000000, 3000000000000000000, 4000000000000000000, 5000000000000000000, 6000000000000000000, 7000000000000000000, 8000000000000000000, 9000000000000000000,
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10000000000000000000
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];
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/// Runtime initialized [`H`] generator.
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static H_PRECOMP: LazyLock<VartimeEdwardsPrecomputation> =
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LazyLock::new(|| VartimeEdwardsPrecomputation::new([*H, ED25519_BASEPOINT_POINT]));
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/// Runtime initialized zero commitment lookup table
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///
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/// # Invariant
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/// This function assumes that the [`ZERO_COMMITMENT_DECOMPOSED_AMOUNT`]
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/// table is sorted.
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pub static ZERO_COMMITMENT_LOOKUP_TABLE: LazyLock<[EdwardsPoint; 172]> = LazyLock::new(|| {
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let mut lookup_table: [EdwardsPoint; 172] = [ED25519_BASEPOINT_POINT; 172];
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for (i, amount) in ZERO_COMMITMENT_DECOMPOSED_AMOUNT.into_iter().enumerate() {
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lookup_table[i] = ED25519_BASEPOINT_POINT + *H * Scalar::from(amount);
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}
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lookup_table
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});
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//---------------------------------------------------------------------------------------------------- Free functions
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/// This function computes the zero commitment given a specific amount.
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///
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/// It will first attempt to lookup into the table of known Pre-RCT value.
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/// Compute it otherwise.
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#[expect(clippy::cast_possible_truncation)]
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pub fn compute_zero_commitment(amount: u64) -> EdwardsPoint {
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// OPTIMIZATION: Unlike monerod which execute a linear search across its lookup
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// table (O(n)). Cuprate is making use of an arithmetic based constant time
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// version (O(1)). It has been benchmarked in both hit and miss scenarios against
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// a binary search lookup (O(log2(n))). To understand the following algorithm it
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// is important to observe the pattern that follows the values of
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// [`ZERO_COMMITMENT_DECOMPOSED_AMOUNT`].
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// First obtain the logarithm base 10 of the amount. and extend it back to obtain
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// the amount without its most significant digit.
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let Some(log) = amount.checked_ilog10() else {
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// amount = 0 so H component is 0.
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return ED25519_BASEPOINT_POINT;
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};
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let div = 10_u64.pow(log);
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// Extract the most significant digit.
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let most_significant_digit = amount / div;
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// If the *rounded* version is different than the exact amount. Then
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// there aren't only trailing zeroes behind the most significant digit.
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// The amount is not part of the table and can calculated apart.
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if most_significant_digit * div != amount {
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return H_PRECOMP.vartime_multiscalar_mul([Scalar::from(amount), Scalar::ONE]);
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}
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// Calculating the index back by progressing within the powers of 10.
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// The index of the first value in the cached amount's row.
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let row_start = u64::from(log) * 9;
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// The index of the cached amount
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let index = (most_significant_digit - 1 + row_start) as usize;
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ZERO_COMMITMENT_LOOKUP_TABLE[index]
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}
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//---------------------------------------------------------------------------------------------------- Tests
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#[cfg(test)]
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mod test {
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use curve25519_dalek::{traits::VartimePrecomputedMultiscalarMul, Scalar};
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use crate::crypto::{compute_zero_commitment, H_PRECOMP, ZERO_COMMITMENT_DECOMPOSED_AMOUNT};
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#[test]
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/// Compare the output of `compute_zero_commitment` for all
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/// preRCT decomposed amounts against their actual computation.
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///
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/// Assert that the lookup table returns the correct commitments
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fn compare_lookup_with_computation() {
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for amount in ZERO_COMMITMENT_DECOMPOSED_AMOUNT {
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let commitment = H_PRECOMP.vartime_multiscalar_mul([Scalar::from(amount), Scalar::ONE]);
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assert!(commitment == compute_zero_commitment(amount));
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}
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}
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}
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@ -30,6 +30,9 @@ pub mod time;
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#[cfg(feature = "tx")]
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pub mod tx;
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#[cfg(feature = "crypto")]
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pub mod crypto;
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//---------------------------------------------------------------------------------------------------- Private Usage
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//----------------------------------------------------------------------------------------------------
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@ -20,7 +20,7 @@ service = ["dep:thread_local", "dep:rayon", "cuprate-helper/thread"]
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[dependencies]
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cuprate-database = { path = "../database" }
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cuprate-database-service = { path = "../service" }
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cuprate-helper = { path = "../../helper", features = ["fs", "map"] }
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cuprate-helper = { path = "../../helper", features = ["fs", "map", "crypto"] }
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cuprate-types = { path = "../../types", features = ["blockchain"] }
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cuprate-pruning = { path = "../../pruning" }
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@ -1,12 +1,13 @@
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//! Output functions.
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//---------------------------------------------------------------------------------------------------- Import
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use curve25519_dalek::{constants::ED25519_BASEPOINT_POINT, edwards::CompressedEdwardsY, Scalar};
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use monero_serai::{generators::H, transaction::Timelock};
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use curve25519_dalek::edwards::CompressedEdwardsY;
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use monero_serai::transaction::Timelock;
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use cuprate_database::{
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RuntimeError, {DatabaseRo, DatabaseRw},
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};
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use cuprate_helper::crypto::compute_zero_commitment;
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use cuprate_helper::map::u64_to_timelock;
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use cuprate_types::OutputOnChain;
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@ -155,9 +156,7 @@ pub fn output_to_output_on_chain(
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amount: Amount,
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table_tx_unlock_time: &impl DatabaseRo<TxUnlockTime>,
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) -> Result<OutputOnChain, RuntimeError> {
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// FIXME: implement lookup table for common values:
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// <https://github.com/monero-project/monero/blob/c8214782fb2a769c57382a999eaf099691c836e7/src/ringct/rctOps.cpp#L322>
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let commitment = ED25519_BASEPOINT_POINT + *H * Scalar::from(amount);
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let commitment = compute_zero_commitment(amount);
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let time_lock = if output
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.output_flags
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@ -2,10 +2,10 @@
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//---------------------------------------------------------------------------------------------------- Import
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use bytemuck::TransparentWrapper;
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use curve25519_dalek::{constants::ED25519_BASEPOINT_POINT, Scalar};
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use monero_serai::transaction::{Input, Timelock, Transaction};
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use cuprate_database::{DatabaseRo, DatabaseRw, RuntimeError, StorableVec};
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use cuprate_helper::crypto::compute_zero_commitment;
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use crate::{
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ops::{
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@ -136,12 +136,9 @@ pub fn add_tx(
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.enumerate()
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.map(|(i, output)| {
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// Create commitment.
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// <https://github.com/Cuprate/cuprate/pull/102#discussion_r1559489302>
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// FIXME: implement lookup table for common values:
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// <https://github.com/monero-project/monero/blob/c8214782fb2a769c57382a999eaf099691c836e7/src/ringct/rctOps.cpp#L322>
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let commitment = if miner_tx {
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ED25519_BASEPOINT_POINT
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+ *monero_serai::generators::H * Scalar::from(output.amount.unwrap_or(0))
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compute_zero_commitment(output.amount.unwrap_or(0))
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} else {
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proofs
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.as_ref()
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