Skeleton for notes and values

src/lib.rs

@@ -9,12 +9,17 @@
 
 mod address;
 pub mod keys;
+mod note;
+pub mod value;
 
 pub use address::Address;
+pub use note::{EncryptedNote, Note, NoteCommitment, Nullifier};
 
 /// Chain-specific constants and constraints for Orchard.
 ///
 /// The purpose of this trait is to encapsulate things like the human-readable prefixes
 /// for encoded addresses, or the range of allowable values for notes.
 pub trait Chain {
+    /// Constraints on values within this chain.
+    type Value: value::Constraint;
 }

src/note.rs

@@ -0,0 +1,34 @@
+use crate::{keys::FullViewingKey, value::NoteValue, Address, Chain};
+
+/// A discrete amount of funds received by an address.
+#[derive(Debug)]
+pub struct Note<C: Chain> {
+    /// The recipient of the funds.
+    recipient: Address<C>,
+    /// The value of this note.
+    value: NoteValue<C::Value>,
+}
+
+impl<C: Chain> Note<C> {
+    /// Derives the commitment to this note.
+    pub fn commitment(&self) -> NoteCommitment {
+        todo!()
+    }
+
+    /// Derives the nullifier for this note.
+    pub fn nullifier(&self, _: &FullViewingKey<C>) -> Nullifier {
+        todo!()
+    }
+}
+
+/// An encrypted note.
+#[derive(Debug)]
+pub struct EncryptedNote;
+
+/// A commitment to a note.
+#[derive(Debug)]
+pub struct NoteCommitment;
+
+/// A unique nullifier for a note.
+#[derive(Debug)]
+pub struct Nullifier;

src/value.rs

@@ -0,0 +1,32 @@
+//! Monetary values within the Orchard shielded pool.
+//!
+//! Values are represented in two places within Orchard:
+//! - The value of an individual note, which is unsigned.
+//! - The sum of note values within an Orchard [`Action`] or [`Bundle`], which is signed.
+//!
+//! We give these separate types within this crate. Users should map these types to their
+//! own general "amount" type as appropriate.
+//!
+//! Inside the circuit, values are constrained to be 63-bit integers.
+//! - TODO: Should this be constrained further to 53 bits? To Zcash's MAX_MONEY?
+//!
+//! [`Action`]: crate::bundle::Action
+//! [`Bundle`]: crate::bundle::Bundle
+
+use std::fmt;
+use std::marker::PhantomData;
+
+/// The constraints applied to Orchard values.
+pub trait Constraint: fmt::Debug {}
+
+/// The value of an individual Orchard note.
+#[derive(Debug)]
+pub struct NoteValue<C: Constraint>(u64, PhantomData<C>);
+
+/// A sum of Orchard note values.
+#[derive(Debug)]
+pub struct ValueSum<C: Constraint>(i64, PhantomData<C>);
+
+/// A commitment to a [`ValueSum`].
+#[derive(Debug)]
+pub struct ValueCommitment;