ntru: add hashing support for streamlined ntru

Signed-off-by: Ahmed <>

ntru/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 [dependencies]
 hybrid-array = { path="../../hybrid-array", features = ["extra-sizes"] }
 rand_core = "0.6.4"
+sha2 = "0.10.8"
 
 [dev-dependencies]
 rayon="1.10.0"

ntru/src/hashes/mod.rs

@@ -0,0 +1,41 @@
+mod streamlined;
+
+use crate::encoded::AsymEnc;
+use hybrid_array::Array;
+use sha2::{Digest, Sha512};
+
+/// # Panics
+/// This functions should never panic
+#[must_use]
+pub fn hash_prefix(b: u8, data: &[u8]) -> [u8; 32] {
+    let mut hasher = Sha512::new();
+    hasher.update([b]);
+    hasher.update(data);
+    let result = hasher.finalize();
+    result[..32].try_into().unwrap()
+}
+/// # Panics
+/// This functions should never panic
+#[must_use]
+pub fn hash_prefix_many(b: u8, data1: &[u8], data2: &[&[u8]]) -> [u8; 32] {
+    let mut hasher = Sha512::new();
+    hasher.update([b]);
+    hasher.update(data1);
+    for data in data2 {
+        hasher.update(data);
+    }
+    let result = hasher.finalize();
+    result[..32].try_into().unwrap()
+}
+
+pub trait HashOps {
+    ///TODO I dont like this api send the first element of y first since it
+    /// is treated differently
+    /// Also I don't want hashing to depend on particular choise of hash function
+    /// maybe users prefer to later switch to sha3
+    fn hash_session(b: u8, y: &[&[u8]]) -> [u8; 32];
+    fn hash_confirm<Params: AsymEnc>(
+        r: &Array<u8, Params::InputsBytes>,
+        cache: &[u8; 32],
+    ) -> [u8; 32];
+}

ntru/src/hashes/streamlined.rs

@@ -0,0 +1,22 @@
+use super::{hash_prefix, hash_prefix_many, HashOps};
+use crate::params::{Streamlined, StreamlinedNtru};
+use hybrid_array::{Array, ArraySize};
+
+impl<P> HashOps for Streamlined<P>
+where
+    P: ArraySize,
+    Streamlined<P>: StreamlinedNtru + Sized,
+{
+    fn hash_session(b: u8, y: &[&[u8]]) -> [u8; 32] {
+        let x = hash_prefix(3, y[0]);
+        hash_prefix_many(b, &x, &y[1..])
+    }
+
+    fn hash_confirm<Params: crate::encoded::AsymEnc>(
+        r: &Array<u8, Params::InputsBytes>,
+        cache: &[u8; 32],
+    ) -> [u8; 32] {
+        let x = hash_prefix(3, r);
+        hash_prefix_many(2, &x, &[cache])
+    }
+}

ntru/src/lib.rs

@@ -22,6 +22,7 @@ mod algebra;
 pub mod const_time;
 mod core;
 pub mod encoded;
+pub mod hashes;
 pub mod params;
 use hybrid_array::sizes::{U1013, U1277, U653, U761, U857, U953};
 use params::{Lpr, Streamlined};