From 3bace28f83e5c00f3680527ce5f1830da25eae61 Mon Sep 17 00:00:00 2001
From: moana <moana@dusk.network>
Date: Thu, 7 Mar 2024 15:20:46 +0100
Subject: [PATCH] Implement `From` for `Domain` for `u64` encoding

Resolves #251
---
 CHANGELOG.md       |  3 +++
 src/hash.rs        | 23 ++++++++++-------------
 src/hash/gadget.rs | 16 +++++-----------
 3 files changed, 18 insertions(+), 24 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 52d3865..6023b14 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Add `Hash` struct [#202]
+- Add `From<Domain> for u64` implementation [#251]
 
 ### Changed
 
@@ -19,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Remove `perm_uses` module as it is obsolete with the introduction of SAFE [#248]
 - Remove `merkle` feature with the introduction of SAFE [#248]
+- Remove `Domain.encoding` method in favor of `From` trait [#251]
 
 ## [0.35.0] - 2024-02-28
 
@@ -465,6 +467,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Variants of sponge for `Scalar` & `Gadget(Variable/LC)`.
 
 <!-- ISSUES -->
+[#251]: https://github.com/dusk-network/poseidon252/issues/251
 [#248]: https://github.com/dusk-network/poseidon252/issues/248
 [#246]: https://github.com/dusk-network/poseidon252/issues/246
 [#243]: https://github.com/dusk-network/poseidon252/issues/243
diff --git a/src/hash.rs b/src/hash.rs
index f1f9dcd..9f4e708 100644
--- a/src/hash.rs
+++ b/src/hash.rs
@@ -29,14 +29,14 @@ pub enum Domain {
     Other,
 }
 
-impl Domain {
+impl From<Domain> for u64 {
     /// Encryption for the domain-separator are taken from section 4.2 of the
     /// paper adapted to u64.
     /// When `Other` is selected we set the domain-separator to zero. We can do
     /// this since the io-pattern will be encoded in the tag in any case,
     /// ensuring safety from collision attacks.
-    pub const fn encoding(&self) -> u64 {
-        match self {
+    fn from(domain: Domain) -> Self {
+        match domain {
             // 2^4 - 1
             Domain::Merkle4 => 0x0000_0000_0000_000f,
             // 2^2 - 1
@@ -107,21 +107,18 @@ impl<'a> Hash<'a> {
 
     /// Finalize the hash.
     pub fn finalize(&self) -> Result<Vec<BlsScalar>, Error> {
-        // generate the io-pattern
-        let io_pattern = io_pattern(self.domain, &self.input, self.output_len)?;
-
-        // set the domain-separator
-        let domain_sep = self.domain.encoding();
-
-        // Generate the hash using the sponge framework.
+        // Generate the hash using the sponge framework:
         // initialize the sponge
-        let mut sponge =
-            Sponge::start(ScalarPermutation::new(), io_pattern, domain_sep)?;
+        let mut sponge = Sponge::start(
+            ScalarPermutation::new(),
+            io_pattern(self.domain, &self.input, self.output_len)?,
+            self.domain.into(),
+        )?;
         // absorb the input
         for input in self.input.iter() {
             sponge.absorb(input.len(), input)?;
         }
-        // squeeze the output
+        // squeeze output_len elements
         sponge.squeeze(self.output_len)?;
 
         // return the result
diff --git a/src/hash/gadget.rs b/src/hash/gadget.rs
index f7867dd..09c9dd4 100644
--- a/src/hash/gadget.rs
+++ b/src/hash/gadget.rs
@@ -46,25 +46,19 @@ impl<'a> HashGadget<'a> {
         &self,
         composer: &mut Composer,
     ) -> Result<Vec<Witness>, Error> {
-        // generate the io-pattern
-        let io_pattern = io_pattern(self.domain, &self.input, self.output_len)?;
-
-        // get the domain-separator
-        let domain_sep = self.domain.encoding();
-
-        // Generate the hash using the sponge framework.
+        // Generate the hash using the sponge framework:
         // initialize the sponge
         let mut sponge = Sponge::start(
             GadgetPermutation::new(composer),
-            io_pattern,
-            domain_sep,
+            io_pattern(self.domain, &self.input, self.output_len)?,
+            self.domain.into(),
         )?;
         // absorb the input
         for input in self.input.iter() {
             sponge.absorb(input.len(), input)?;
         }
-        // squeeze the output
-        sponge.squeeze(self.output_len as usize)?;
+        // squeeze output_len elements
+        sponge.squeeze(self.output_len)?;
 
         // return the result
         Ok(sponge.finish()?)