From 2e168204f073e72549c661f61293beaa82004d7f Mon Sep 17 00:00:00 2001
From: Luke Parker <lukeparker5132@gmail.com>
Date: Thu, 30 Jun 2022 03:17:15 -0400
Subject: [PATCH] Implement PrimeFieldBits for dalek-ff-group

---
 crypto/dalek-ff-group/Cargo.toml |  1 +
 crypto/dalek-ff-group/src/lib.rs | 18 +++++++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/crypto/dalek-ff-group/Cargo.toml b/crypto/dalek-ff-group/Cargo.toml
index 0904138f..3b78578f 100644
--- a/crypto/dalek-ff-group/Cargo.toml
+++ b/crypto/dalek-ff-group/Cargo.toml
@@ -14,6 +14,7 @@ digest = "0.10"
 
 subtle = "2.4"
 
+ff = "0.12"
 group = "0.12"
 
 curve25519-dalek =  "3.2"
diff --git a/crypto/dalek-ff-group/src/lib.rs b/crypto/dalek-ff-group/src/lib.rs
index 5340b7e2..e2ed5e75 100644
--- a/crypto/dalek-ff-group/src/lib.rs
+++ b/crypto/dalek-ff-group/src/lib.rs
@@ -29,7 +29,8 @@ use dalek::{
   }
 };
 
-use group::{ff::{Field, PrimeField}, Group, GroupEncoding, prime::PrimeGroup};
+use ff::{Field, PrimeField, FieldBits, PrimeFieldBits};
+use group::{Group, GroupEncoding, prime::PrimeGroup};
 
 macro_rules! deref_borrow {
   ($Source: ident, $Target: ident) => {
@@ -190,6 +191,21 @@ impl PrimeField for Scalar {
   fn root_of_unity() -> Self { unimplemented!() }
 }
 
+impl PrimeFieldBits for Scalar {
+  type ReprBits = [u8; 32];
+
+  fn to_le_bits(&self) -> FieldBits<Self::ReprBits> {
+    self.to_repr().into()
+  }
+
+  fn char_le_bits() -> FieldBits<Self::ReprBits> {
+    let mut bytes = (Scalar::zero() - Scalar::one()).to_repr();
+    bytes[0] += 1;
+    debug_assert_eq!(Scalar::from_bytes_mod_order(bytes), Scalar::zero());
+    bytes.into()
+  }
+}
+
 macro_rules! dalek_group {
   (
     $Point: ident,