Stub out the sign/verify API.

src/public_key.rs

@@ -1,6 +1,6 @@
 use std::convert::TryFrom;
 
-use crate::Error;
+use crate::{Error, Signature};
 
 /// A refinement type indicating that the inner `[u8; 32]` represents an
 /// encoding of a RedJubJub public key.
@@ -39,3 +39,11 @@ impl TryFrom<PublicKeyBytes> for PublicKey {
         unimplemented!();
     }
 }
+
+// This is similar to impl signature::Verifier but without boxed errors
+impl PublicKey {
+    /// Verify a supposed `signature` over `msg` made by this public key.
+    pub fn verify(&self, msg: &[u8], signature: &Signature) -> Result<(), Error> {
+        unimplemented!();
+    }
+}

src/secret_key.rs

@@ -1,6 +1,6 @@
 use std::convert::TryFrom;
 
-use crate::Error;
+use crate::{Error, PublicKey, Signature};
 
 /// A refinement type indicating that the inner `[u8; 32]` represents an
 /// encoding of a RedJubJub secret key.
@@ -32,6 +32,7 @@ impl From<SecretKey> for SecretKeyBytes {
     }
 }
 
+// XXX could this be a From impl?
 impl TryFrom<SecretKeyBytes> for SecretKey {
     type Error = Error;
 
@@ -39,3 +40,17 @@ impl TryFrom<SecretKeyBytes> for SecretKey {
         unimplemented!();
     }
 }
+
+impl<'a> From<&'a SecretKey> for PublicKey {
+    fn from(sk: &'a SecretKey) -> PublicKey {
+        unimplemented!();
+    }
+}
+
+// Similar to signature::Signer but without boxed errors.
+impl SecretKey {
+    /// Sign the given `msg` with this `SecretKey`.
+    pub fn sign(&self, msg: &[u8]) -> Signature {
+        unimplemented!();
+    }
+}