adds a power reducing utility

powersoftau/src/bin/reduce_powers.rs

@@ -0,0 +1,118 @@
+extern crate powersoftau;
+extern crate rand;
+extern crate blake2;
+extern crate byteorder;
+extern crate bellman_ce;
+
+use bellman_ce::pairing::{CurveAffine, CurveProjective};
+use bellman_ce::pairing::bn256::Bn256;
+use bellman_ce::pairing::bn256::{G1, G2};
+use powersoftau::small_bn256::{Bn256CeremonyParameters};
+use powersoftau::batched_accumulator::*;
+use powersoftau::parameters::{UseCompression};
+use powersoftau::utils::{reduced_hash};
+use powersoftau::*;
+
+use crate::parameters::*;
+
+use bellman_ce::multicore::Worker;
+use bellman_ce::domain::{EvaluationDomain, Point};
+
+use std::fs::OpenOptions;
+use std::io::{BufWriter, Write};
+
+use memmap::*;
+
+#[derive(Clone)]
+pub struct Bn256ReducedCeremonyParameters {
+
+}
+
+impl PowersOfTauParameters for Bn256ReducedCeremonyParameters {
+    const REQUIRED_POWER: usize = 10;
+
+    // This ceremony is based on the BN256 elliptic curve construction.
+    const G1_UNCOMPRESSED_BYTE_SIZE: usize = 64;
+    const G2_UNCOMPRESSED_BYTE_SIZE: usize = 128;
+    const G1_COMPRESSED_BYTE_SIZE: usize = 32;
+    const G2_COMPRESSED_BYTE_SIZE: usize = 64;
+}
+
+const fn num_bits<T>() -> usize { std::mem::size_of::<T>() * 8 }
+
+fn log_2(x: u64) -> u32 {
+    assert!(x > 0);
+    num_bits::<u64>() as u32 - x.leading_zeros() - 1
+}
+
+fn main() {
+    // Try to load `./challenge` from disk.
+    let reader = OpenOptions::new()
+                            .read(true)
+                            .open("challenge")
+                            .expect("unable open `./challenge` in this directory");
+    let challenge_readable_map = unsafe { MmapOptions::new().map(&reader).expect("unable to create a memory map for input") };
+
+    let current_accumulator = BachedAccumulator::<Bn256, Bn256CeremonyParameters>::deserialize(
+        &challenge_readable_map,
+        CheckForCorrectness::Yes,
+        UseCompression::No,
+    ).expect("unable to read compressed accumulator");
+
+    let mut reduced_accumulator = BachedAccumulator::<Bn256, Bn256ReducedCeremonyParameters>::empty();
+    reduced_accumulator.tau_powers_g1 = current_accumulator.tau_powers_g1[..Bn256ReducedCeremonyParameters::TAU_POWERS_G1_LENGTH].to_vec();
+    reduced_accumulator.tau_powers_g2 = current_accumulator.tau_powers_g2[..Bn256ReducedCeremonyParameters::TAU_POWERS_LENGTH].to_vec();
+    reduced_accumulator.alpha_tau_powers_g1 = current_accumulator.alpha_tau_powers_g1[..Bn256ReducedCeremonyParameters::TAU_POWERS_LENGTH].to_vec();
+    reduced_accumulator.beta_tau_powers_g1 = current_accumulator.beta_tau_powers_g1[..Bn256ReducedCeremonyParameters::TAU_POWERS_LENGTH].to_vec();
+    reduced_accumulator.beta_g2 = current_accumulator.beta_g2;
+
+    let writer = OpenOptions::new()
+                            .read(true)
+                            .write(true)
+                            .create_new(true)
+                            .open("reduced_challenge").expect("unable to create `./reduced_challenge` in this directory");
+
+
+
+    // Recomputation stips the public key and uses hashing to link with the previous contibution after decompression
+    writer.set_len(Bn256ReducedCeremonyParameters::ACCUMULATOR_BYTE_SIZE as u64).expect("must make output file large enough");
+
+    let mut writable_map = unsafe { MmapOptions::new().map_mut(&writer).expect("unable to create a memory map for output") };
+
+    let hash = reduced_hash(Bn256CeremonyParameters::REQUIRED_POWER as u8, Bn256ReducedCeremonyParameters::REQUIRED_POWER as u8);
+    (&mut writable_map[0..]).write(hash.as_slice()).expect("unable to write a default hash to mmap");
+    writable_map.flush().expect("unable to write reduced hash to `./reduced_challenge`");
+
+    println!("Reduced hash for a reduced challenge:");
+    for line in hash.as_slice().chunks(16) {
+        print!("\t");
+        for section in line.chunks(4) {
+            for b in section {
+                print!("{:02x}", b);
+            }
+            print!(" ");
+        }
+        println!("");
+    }
+
+    reduced_accumulator.serialize(&mut writable_map, UseCompression::No);
+
+    // Get the hash of the contribution, so the user can compare later
+    let output_readonly = writable_map.make_read_only().expect("must make a map readonly");
+    let contribution_hash = BachedAccumulator::<Bn256, Bn256ReducedCeremonyParameters>::calculate_hash(&output_readonly);
+
+    println!("Reduced contribution is formed with a hash:");
+
+    for line in contribution_hash.as_slice().chunks(16) {
+        print!("\t");
+        for section in line.chunks(4) {
+            for b in section {
+                print!("{:02x}", b);
+            }
+            print!(" ");
+        }
+        println!("");
+    }
+
+    println!("Wrote a reduced accumulator to `./challenge`");
+}

powersoftau/src/utils.rs

@@ -140,6 +140,14 @@ pub fn blank_hash() -> GenericArray<u8, U64> {
     Blake2b::new().result()
 }
 
+pub fn reduced_hash(old_power: u8, new_power: u8) -> GenericArray<u8, U64> {
+    let mut hasher = Blake2b::new();
+    hasher.input(&[old_power, new_power]);
+    hasher.result()
+}
+
+
+
 /// Checks if pairs have the same ratio.
 /// Under the hood uses pairing to check
 /// x1/x2 = y1/y2 => x1*y2 = x2*y1