Add field arithmetic skeleton

.gitignore

@@ -8,3 +8,12 @@ Cargo.lock
 
 # These are backup files generated by rustfmt
 **/*.rs.bk
+
+
+#Added by cargo
+#
+#already existing elements are commented out
+
+/target
+#**/*.rs.bk
+#Cargo.lock

Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "doppio"
+version = "0.1.0"
+authors = ["Cathie Yun <[email protected]>", "Henry de Valence <[email protected]>"]
+edition = "2018"
+
+
+[dependencies]
+curve25519-dalek = "1.1.3"

src/field.rs

@@ -0,0 +1,81 @@
+//! Field arithmetic for the doppio curve.
+//!
+//! Because doppio is intended for use in ristretto255-based proof
+//! systems, the scalar field of ristretto255 is the *ground field*
+//! for doppio.
+//!
+//! This implementation is derived from the 52-bit scalar
+//! implementation contributed to `curve25519-dalek` by Andrew Moon.
+
+use std::default::Default;
+use std::ops::{Add, Mul, Sub};
+
+use crate::Ristretto255Scalar;
+
+/// A field element modulo \\(2\^{252} +
+/// 27742317777372353535851937790883648493\\), the ground field for
+/// the doppio curve and the scalar field for the ristretto255 group.
+#[derive(Copy, Clone, Debug)]
+pub struct FieldElement([u64; 5]);
+
+impl Add<FieldElement> for FieldElement {
+    type Output = FieldElement;
+    fn add(self, rhs: FieldElement) -> FieldElement {
+        unimplemented!();
+    }
+}
+
+impl Sub<FieldElement> for FieldElement {
+    type Output = FieldElement;
+    fn sub(self, rhs: FieldElement) -> FieldElement {
+        unimplemented!();
+    }
+}
+
+impl Mul<FieldElement> for FieldElement {
+    type Output = FieldElement;
+    fn mul(self, rhs: FieldElement) -> FieldElement {
+        unimplemented!();
+    }
+}
+
+impl Default for FieldElement {
+    fn default() -> FieldElement {
+        FieldElement::zero()
+    }
+}
+
+impl From<Ristretto255Scalar> for FieldElement {
+    fn from(packed: Ristretto255Scalar) -> FieldElement {
+        unimplemented!();
+    }
+}
+
+impl Into<Ristretto255Scalar> for FieldElement {
+    fn into(self) -> Ristretto255Scalar {
+        unimplemented!();
+    }
+}
+
+impl FieldElement {
+    pub fn zero() -> FieldElement {
+        FieldElement([0; 5])
+    }
+
+    pub fn one() -> FieldElement {
+        // This needs to return 1/R mod l
+        unimplemented!();
+    }
+
+    pub fn invert(&self) -> FieldElement {
+        unimplemented!();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}

src/lib.rs

@@ -0,0 +1,11 @@
+pub type Ristretto255Scalar = curve25519_dalek::scalar::Scalar;
+
+mod field;
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}