Merge pull request #10 from ZcashFoundation/conversions

Add conversions for SecretKey -> PublicKey

src/constants.rs

@@ -0,0 +1,15 @@
+/// The byte-encoding of the basepoint for `SpendAuthSig`.
+// Extracted ad-hoc from librustzcash
+// XXX add tests for this value.
+pub const SPENDAUTHSIG_BASEPOINT_BYTES: [u8; 32] = [
+    48, 181, 242, 170, 173, 50, 86, 48, 188, 221, 219, 206, 77, 103, 101, 109, 5, 253, 28, 194,
+    208, 55, 187, 83, 117, 182, 233, 109, 158, 1, 161, 215,
+];
+
+/// The byte-encoding of the basepoint for `BindingSig`.
+// Extracted ad-hoc from librustzcash
+// XXX add tests for this value.
+pub const BINDINGSIG_BASEPOINT_BYTES: [u8; 32] = [
+    139, 106, 11, 56, 185, 250, 174, 60, 59, 128, 59, 71, 176, 241, 70, 173, 80, 171, 34, 30, 110,
+    42, 251, 230, 219, 222, 69, 203, 169, 211, 129, 237,
+];

src/error.rs

@@ -3,7 +3,10 @@ use thiserror::Error;
 /// An error related to RedJubJub signatures.
 #[derive(Error, Debug)]
 pub enum Error {
-    /// This is a stub variant to check that thiserror derive works.
-    #[error("Stub error--  remove this.")]
-    StubError,
+    /// The encoding of a secret key was malformed.
+    #[error("Malformed secret key encoding.")]
+    MalformedSecretKey,
+    /// The encoding of a public key was malformed.
+    #[error("Malformed public key encoding.")]
+    MalformedPublicKey,
 }

src/lib.rs

@@ -4,6 +4,7 @@
 
 //! Docs require the `nightly` feature until RFC 1990 lands.
 
+mod constants;
 mod error;
 mod public_key;
 mod secret_key;
@@ -12,6 +13,9 @@ mod signature;
 /// An element of the JubJub scalar field used for randomization of public and secret keys.
 pub type Randomizer = jubjub::Fr;
 
+/// A better name than Fr.
+type Scalar = jubjub::Fr;
+
 pub use error::Error;
 pub use public_key::{PublicKey, PublicKeyBytes};
 pub use secret_key::{SecretKey, SecretKeyBytes};
@@ -44,11 +48,3 @@ mod private {
     impl Sealed for Binding {}
     impl Sealed for SpendAuth {}
 }
-
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}

src/public_key.rs

@@ -1,6 +1,6 @@
 use std::{convert::TryFrom, marker::PhantomData};
 
-use crate::{Error, SigType, SpendAuth, Binding, Randomizer, Signature};
+use crate::{Binding, Error, Randomizer, SigType, Signature, SpendAuth};
 
 /// A refinement type indicating that the inner `[u8; 32]` represents an
 /// encoding of a RedJubJub public key.
@@ -12,7 +12,10 @@ pub struct PublicKeyBytes<T: SigType> {
 
 impl<T: SigType> From<[u8; 32]> for PublicKeyBytes<T> {
     fn from(bytes: [u8; 32]) -> PublicKeyBytes<T> {
-        PublicKeyBytes { bytes, _marker: PhantomData }
+        PublicKeyBytes {
+            bytes,
+            _marker: PhantomData,
+        }
     }
 }
 
@@ -26,13 +29,17 @@ impl<T: SigType> From<PublicKeyBytes<T>> for [u8; 32] {
 // XXX PartialEq, Eq?
 #[derive(Copy, Clone, Debug)]
 pub struct PublicKey<T: SigType> {
-    // fields
-    _marker: PhantomData<T>,
+    // XXX-jubjub: this should just be Point
+    pub(crate) point: jubjub::ExtendedPoint,
+    // XXX should this just store a PublicKeyBytes?
+    pub(crate) bytes: [u8; 32],
+    pub(crate) _marker: PhantomData<T>,
 }
 
 impl<T: SigType> From<PublicKey<T>> for PublicKeyBytes<T> {
     fn from(pk: PublicKey<T>) -> PublicKeyBytes<T> {
-        unimplemented!();
+        let PublicKey { bytes, _marker, .. } = pk;
+        PublicKeyBytes { bytes, _marker }
     }
 }
 
@@ -40,7 +47,18 @@ impl<T: SigType> TryFrom<PublicKeyBytes<T>> for PublicKey<T> {
     type Error = Error;
 
     fn try_from(bytes: PublicKeyBytes<T>) -> Result<Self, Self::Error> {
-        unimplemented!();
+        // XXX-jubjub: this should not use CtOption
+        // XXX-jubjub: this takes ownership of bytes, while Fr doesn't.
+        let maybe_point = jubjub::AffinePoint::from_bytes(bytes.bytes);
+        if maybe_point.is_some().into() {
+            Ok(PublicKey {
+                point: maybe_point.unwrap().into(),
+                bytes: bytes.bytes,
+                _marker: PhantomData,
+            })
+        } else {
+            Err(Error::MalformedPublicKey)
+        }
     }
 }
 

src/secret_key.rs

@@ -1,6 +1,6 @@
 use std::{convert::TryFrom, marker::PhantomData};
 
-use crate::{Error, PublicKey, SigType, Binding, SpendAuth, Randomizer, Signature};
+use crate::{Binding, Error, PublicKey, Randomizer, Scalar, SigType, Signature, SpendAuth};
 
 /// A refinement type indicating that the inner `[u8; 32]` represents an
 /// encoding of a RedJubJub secret key.
@@ -12,7 +12,10 @@ pub struct SecretKeyBytes<T: SigType> {
 
 impl<T: SigType> From<[u8; 32]> for SecretKeyBytes<T> {
     fn from(bytes: [u8; 32]) -> SecretKeyBytes<T> {
-        SecretKeyBytes{ bytes, _marker: PhantomData }
+        SecretKeyBytes {
+            bytes,
+            _marker: PhantomData,
+        }
     }
 }
 
@@ -26,28 +29,72 @@ impl<T: SigType> From<SecretKeyBytes<T>> for [u8; 32] {
 // XXX PartialEq, Eq?
 #[derive(Copy, Clone, Debug)]
 pub struct SecretKey<T: SigType> {
-    // fields
+    sk: Scalar,
     _marker: PhantomData<T>,
 }
 
 impl<T: SigType> From<SecretKey<T>> for SecretKeyBytes<T> {
-    fn from(pk: SecretKey<T>) -> SecretKeyBytes<T> {
-        unimplemented!();
+    fn from(sk: SecretKey<T>) -> SecretKeyBytes<T> {
+        SecretKeyBytes {
+            bytes: sk.sk.to_bytes(),
+            _marker: PhantomData,
+        }
     }
 }
 
 // XXX could this be a From impl?
+// not unless there's an infallible conversion from bytes to scalars,
+// which is not  currently present in jubjub
 impl<T: SigType> TryFrom<SecretKeyBytes<T>> for SecretKey<T> {
     type Error = Error;
 
     fn try_from(bytes: SecretKeyBytes<T>) -> Result<Self, Self::Error> {
-        unimplemented!();
+        // XXX-jubjub: it does not make sense for this to be a CtOption...
+        // XXX-jubjub: this takes a borrow but point deser doesn't
+        let maybe_sk = Scalar::from_bytes(&bytes.bytes);
+        if maybe_sk.is_some().into() {
+            Ok(SecretKey {
+                sk: maybe_sk.unwrap(),
+                _marker: PhantomData,
+            })
+        } else {
+            Err(Error::MalformedSecretKey)
+        }
     }
 }
 
-impl<'a, T: SigType> From<&'a SecretKey<T>> for PublicKey<T> {
-    fn from(sk: &'a SecretKey<T>) -> PublicKey<T> {
-        unimplemented!();
+impl<'a> From<&'a SecretKey<SpendAuth>> for PublicKey<SpendAuth> {
+    fn from(sk: &'a SecretKey<SpendAuth>) -> PublicKey<SpendAuth> {
+        // XXX-jubjub: this is pretty baroque
+        // XXX-jubjub: provide basepoint tables for generators
+        let basepoint: jubjub::ExtendedPoint =
+            jubjub::AffinePoint::from_bytes(crate::constants::SPENDAUTHSIG_BASEPOINT_BYTES)
+                .unwrap()
+                .into();
+        pk_from_sk_inner(sk, basepoint)
+    }
+}
+
+impl<'a> From<&'a SecretKey<Binding>> for PublicKey<Binding> {
+    fn from(sk: &'a SecretKey<Binding>) -> PublicKey<Binding> {
+        let basepoint: jubjub::ExtendedPoint =
+            jubjub::AffinePoint::from_bytes(crate::constants::BINDINGSIG_BASEPOINT_BYTES)
+                .unwrap()
+                .into();
+        pk_from_sk_inner(sk, basepoint)
+    }
+}
+
+fn pk_from_sk_inner<T: SigType>(
+    sk: &SecretKey<T>,
+    basepoint: jubjub::ExtendedPoint,
+) -> PublicKey<T> {
+    let point = &basepoint * &sk.sk;
+    let bytes = jubjub::AffinePoint::from(&point).to_bytes();
+    PublicKey {
+        point,
+        bytes,
+        _marker: PhantomData,
     }
 }
 

src/signature.rs

@@ -1,4 +1,4 @@
-use std::{marker::PhantomData, convert, fmt};
+use std::{convert, fmt, marker::PhantomData};
 
 use crate::SigType;
 
@@ -11,7 +11,8 @@ pub struct Signature<T: SigType> {
 impl<T: SigType> From<[u8; 64]> for Signature<T> {
     fn from(bytes: [u8; 64]) -> Signature<T> {
         Signature {
-            bytes, _marker: PhantomData,
+            bytes,
+            _marker: PhantomData,
         }
     }
 }
@@ -39,7 +40,8 @@ impl<T: SigType> Clone for Signature<T> {
         let mut bytes = [0; 64];
         bytes[..].copy_from_slice(&self.bytes[..]);
         Signature {
-            bytes, _marker: PhantomData,
+            bytes,
+            _marker: PhantomData,
         }
     }
 }