commit 6821b0f57456e43b3a2830595716e50f94418e6d
Author: kilic <kiliconu@itu.edu.tr>
Date:   Thu Apr 23 20:55:24 2020 +0300

    initial commit with draft poseidon

diff --git a/.gitignore b/.gitignore
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+++ b/.gitignore
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+/target
+Cargo.lock
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diff --git a/Cargo.toml b/Cargo.toml
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+++ b/Cargo.toml
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+[package]
+name = "rln"
+version = "0.1.0"
+authors = ["Onur Kılıç <onurkilic@itu.edu.tr>"]
+edition = "2018"
+
+[dependencies]
+rand = "0.4"
+blake2 = "0.8.1"
+sapling-crypto = { package = "sapling-crypto_ce", version = "0.1.2" }
diff --git a/README.md b/README.md
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+++ b/README.md
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+# RLN
+
+[wip doc](https://hackmd.io/tMTLMYmTR5eynw2lwK9n1w?view)
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diff --git a/rustfmt.toml b/rustfmt.toml
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+ max_width = 120
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diff --git a/src/lib.rs b/src/lib.rs
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+++ b/src/lib.rs
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+#![allow(dead_code)]
+#![allow(unused_imports)]
+
+mod poseidon;
diff --git a/src/poseidon.rs b/src/poseidon.rs
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+++ b/src/poseidon.rs
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+use blake2::{Blake2s, Digest};
+
+use sapling_crypto::bellman::pairing::bn256;
+use sapling_crypto::bellman::pairing::bn256::{Bn256, Fr};
+use sapling_crypto::bellman::pairing::ff::{Field, PrimeField, PrimeFieldRepr};
+
+#[test]
+fn test_poseidon() {
+  let (t, rf, rp) = (3usize, 8usize, 57usize);
+  let mut hasher = Blake2s::new();
+  hasher.input(b"rln poseidion t3rf4rp57");
+  let seed = hasher.result().to_vec();
+  let person_full_round_constant = b"rlnhds01";
+  let full_round_constants = PoseidonParams::generate_constants(person_full_round_constant, seed.clone(), rf);
+  let person_partial_round_constant = b"rlnhds02";
+  let partial_round_constants = PoseidonParams::generate_constants(person_partial_round_constant, seed.clone(), rp);
+  let person_mds_matrix = b"rlnhds03";
+  let mds_matrix = PoseidonParams::generate_mds_matrix(person_mds_matrix, seed.clone(), t);
+  let mut constants: Vec<Fr> = Vec::new();
+  for i in 0..rf / 2 {
+    constants.push(full_round_constants[i]);
+  }
+  for i in 0..rp {
+    constants.push(partial_round_constants[i]);
+  }
+  for i in 0..rf / 2 {
+    constants.push(full_round_constants[i]);
+  }
+  let mut hasher = Poseidon::new_with_params(rf, rp, t, constants, mds_matrix);
+  let input = [Fr::zero()];
+  let r1 = hasher.hash(&input);
+  let r2 = hasher.hash(&input);
+  assert_eq!(r1, r2, "just to see if internal state resets");
+}
+
+struct PoseidonParams {
+  rf: usize,
+  rp: usize,
+  t: usize,
+  round_constants: Vec<Fr>,
+  mds_matrix: Vec<Fr>,
+}
+
+impl PoseidonParams {
+  pub fn new(rf: usize, rp: usize, t: usize, round_constants: Vec<Fr>, mds_matrix: Vec<Fr>) -> PoseidonParams {
+    assert_eq!(rf + rp, round_constants.len());
+    PoseidonParams {
+      rf,
+      rp,
+      t,
+      round_constants,
+      mds_matrix,
+    }
+  }
+  pub fn generate_mds_matrix(persona: &[u8; 8], seed: Vec<u8>, t: usize) -> Vec<Fr> {
+    let mut matrix: Vec<Fr> = Vec::with_capacity(t * t);
+    let mut xs: Vec<Fr> = Vec::with_capacity(t);
+    let mut ys: Vec<Fr> = Vec::with_capacity(t);
+    let mut source = seed.clone();
+    loop {
+      let mut hasher = Blake2s::new();
+      hasher.input(persona);
+      hasher.input(source);
+      source = hasher.result().to_vec();
+      let mut candidate_repr = <bn256::Fr as PrimeField>::Repr::default();
+      candidate_repr.read_le(&source[..]).unwrap();
+      if let Ok(candidate) = bn256::Fr::from_repr(candidate_repr) {
+        xs.push(candidate);
+        if xs.len() == t {
+          break;
+        }
+      }
+    }
+    loop {
+      let mut hasher = Blake2s::new();
+      hasher.input(persona);
+      hasher.input(source);
+      source = hasher.result().to_vec();
+      let mut candidate_repr = <bn256::Fr as PrimeField>::Repr::default();
+      candidate_repr.read_le(&source[..]).unwrap();
+      if let Ok(candidate) = bn256::Fr::from_repr(candidate_repr) {
+        ys.push(candidate);
+        if ys.len() == t {
+          break;
+        }
+      }
+    }
+    for i in 0..t {
+      for j in 0..t {
+        let mut tmp = xs[i];
+        tmp.add_assign(&ys[j]);
+        let entry = tmp.inverse().unwrap();
+        matrix.insert((i * t) + j, entry);
+      }
+    }
+    matrix
+  }
+
+  fn generate_constants(persona: &[u8; 8], seed: Vec<u8>, len: usize) -> Vec<Fr> {
+    let mut constants: Vec<Fr> = Vec::new();
+    let mut source = seed.clone();
+    loop {
+      let mut hasher = Blake2s::new();
+      hasher.input(persona);
+      hasher.input(source);
+      source = hasher.result().to_vec();
+      let mut candidate_repr = <bn256::Fr as PrimeField>::Repr::default();
+      candidate_repr.read_le(&source[..]).unwrap();
+      if let Ok(candidate) = bn256::Fr::from_repr(candidate_repr) {
+        constants.push(candidate);
+        if constants.len() == len {
+          break;
+        }
+      }
+    }
+    constants
+  }
+}
+
+struct Poseidon {
+  state: Vec<Fr>,
+  round: usize,
+  params: PoseidonParams,
+}
+
+impl Poseidon {
+  pub fn new_with_params(rf: usize, rp: usize, t: usize, round_constants: Vec<Fr>, mds_matrix: Vec<Fr>) -> Poseidon {
+    let params = PoseidonParams::new(rf, rp, t, round_constants, mds_matrix);
+    Poseidon::new(params)
+  }
+  pub fn new(params: PoseidonParams) -> Poseidon {
+    Poseidon {
+      round: 0,
+      state: Vec::new(),
+      params,
+    }
+  }
+
+  pub fn hash(&mut self, inputs: &[Fr]) -> Fr {
+    self.new_state(inputs);
+    while self.round() {}
+    self.round = 0;
+    self.result()
+  }
+
+  fn new_state(&mut self, inputs: &[Fr]) {
+    let t = self.t();
+    assert!(inputs.len() < t);
+    self.state = inputs.to_vec();
+    self.state.resize(t, Fr::zero());
+  }
+
+  fn t(&self) -> usize {
+    self.params.t
+  }
+
+  fn result(&self) -> Fr {
+    self.state[0]
+  }
+
+  fn round(&mut self) -> bool {
+    let a1 = self.params.rf / 2;
+    let a2 = self.params.rf / 2 + self.params.rp;
+    let a3 = self.params.rf + self.params.rp;
+
+    if self.round < a1 {
+      self.full_round();
+      false
+    } else if self.round >= a1 && self.round < a2 {
+      self.partial_round();
+      false
+    } else if self.round >= a2 && self.round < a3 {
+      self.full_round();
+      false
+    } else {
+      true
+    }
+  }
+
+  fn full_round(&mut self) {
+    self.add_round_constants();
+    self.apply_quintic_sbox();
+    self.mul_mds_matrix();
+  }
+
+  fn full_round_no_mds(&mut self) {
+    self.add_round_constants();
+    self.apply_quintic_sbox();
+  }
+
+  fn partial_round(&mut self) {
+    self.add_round_constants();
+    self.apply_quintic_sbox();
+    self.mul_mds_matrix();
+  }
+
+  fn add_round_constants(&mut self) {
+    let w = self.params.t;
+    // use zip
+    for (j, b) in self.state.iter_mut().enumerate() {
+      let c = self.params.round_constants[self.round * w + j];
+      b.add_assign(&c);
+    }
+  }
+
+  fn apply_quintic_sbox(&mut self) {
+    for s in self.state.iter_mut() {
+      let mut b = s.clone();
+      b.square();
+      b.square();
+      s.mul_assign(&b);
+    }
+  }
+
+  fn mul_mds_matrix(&mut self) {
+    let w = self.params.t;
+    let mut new_state = vec![Fr::zero(); w];
+    for (i, ns) in new_state.iter_mut().enumerate() {
+      // slice and zip
+      for (j, s) in self.state.iter().enumerate() {
+        let mut tmp = s.clone();
+        tmp.mul_assign(&self.params.mds_matrix[i * w + j]);
+        ns.add_assign(&tmp);
+      }
+    }
+    self.state = new_state;
+  }
+}