elliptic-curve: add Invert trait

elliptic-curve/src/lib.rs

@@ -22,6 +22,7 @@
 extern crate std;
 
 pub mod error;
+pub mod ops;
 pub mod secret_key;
 
 // TODO(tarcieri): other curve forms

elliptic-curve/src/ops.rs

@@ -0,0 +1,12 @@
+//! Traits for arithmetic operations on elliptic curve field elements
+
+use subtle::CtOption;
+
+/// Perform an inversion on a field element (i.e. base field element or scalar)
+pub trait Invert {
+    /// Field element type
+    type Output;
+
+    /// Invert a field element.
+    fn invert(&self) -> CtOption<Self::Output>;
+}