From 57687cf70fee8c797211900226dbe406d0cc57fb Mon Sep 17 00:00:00 2001
From: Sean Bowe <ewillbefull@gmail.com>
Date: Sat, 24 Feb 2018 22:53:00 -0700
Subject: [PATCH] Creation of the Note primitive.

---
 src/lib.rs            |  1 +
 src/pedersen_hash.rs  |  2 +-
 src/primitives/mod.rs | 65 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100644 src/primitives/mod.rs

diff --git a/src/lib.rs b/src/lib.rs
index 48af45c..4a08bf9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,3 +14,4 @@ pub mod jubjub;
 pub mod circuit;
 pub mod group_hash;
 pub mod pedersen_hash;
+pub mod primitives;
diff --git a/src/pedersen_hash.rs b/src/pedersen_hash.rs
index 12e5c7d..1eb75f6 100644
--- a/src/pedersen_hash.rs
+++ b/src/pedersen_hash.rs
@@ -1,7 +1,7 @@
 use jubjub::*;
 use pairing::*;
 
-use circuit::pedersen_hash::Personalization;
+pub use circuit::pedersen_hash::Personalization;
 
 pub fn pedersen_hash<E, I>(
     personalization: Personalization,
diff --git a/src/primitives/mod.rs b/src/primitives/mod.rs
new file mode 100644
index 0000000..7a99092
--- /dev/null
+++ b/src/primitives/mod.rs
@@ -0,0 +1,65 @@
+use pedersen_hash::{
+    pedersen_hash,
+    Personalization
+};
+
+use byteorder::{
+    BigEndian,
+    ByteOrder
+};
+
+use jubjub::{
+    JubjubEngine,
+    JubjubParams,
+    edwards,
+    PrimeOrder,
+    FixedGenerators
+};
+
+pub struct Note<E: JubjubEngine> {
+    /// The value of the note
+    pub value: u64,
+    /// The diversified base of the address, GH(d)
+    pub g_d: edwards::Point<E, PrimeOrder>,
+    /// The public key of the address, g_d^ivk
+    pub pk_d: edwards::Point<E, PrimeOrder>,
+    /// The commitment randomness
+    pub r: E::Fs
+}
+
+impl<E: JubjubEngine> Note<E> {
+    /// Computes the note commitment
+    pub fn cm(&self, params: &E::Params) -> E::Fr
+    {
+        // Calculate the note contents, as bytes
+        let mut note_contents = vec![];
+
+        // Write the value in big endian
+        BigEndian::write_u64(&mut note_contents, self.value);
+
+        // Write g_d
+        self.g_d.write(&mut note_contents).unwrap();
+
+        // Write pk_d
+        self.pk_d.write(&mut note_contents).unwrap();
+
+        // Compute the Pedersen hash of the note contents
+        let hash_of_contents = pedersen_hash(
+            Personalization::NoteCommitment,
+            note_contents.into_iter()
+                         .flat_map(|byte| {
+                            (0..8).rev().map(move |i| ((byte >> i) & 1) == 1)
+                         }),
+            params
+        );
+
+        // Compute final commitment
+        let cm = params.generator(FixedGenerators::NoteCommitmentRandomness)
+                       .mul(self.r, params)
+                       .add(&hash_of_contents, params);
+
+        // The commitment is in the prime order subgroup, so mapping the
+        // commitment to the x-coordinate is an injective encoding.
+        cm.into_xy().0
+    }
+}