diff --git a/src/error.rs b/src/error.rs
index a7c55d8..617773a 100644
--- a/src/error.rs
+++ b/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,
 }
diff --git a/src/lib.rs b/src/lib.rs
index ef2ad7f..7ca40cf 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,6 +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};
diff --git a/src/public_key.rs b/src/public_key.rs
index 978ee3a..a08bfba 100644
--- a/src/public_key.rs
+++ b/src/public_key.rs
@@ -29,13 +29,17 @@ impl<T: SigType> From<PublicKeyBytes<T>> for [u8; 32] {
 // XXX PartialEq, Eq?
 #[derive(Copy, Clone, Debug)]
 pub struct PublicKey<T: SigType> {
-    // fields
+    // XXX-jubjub: this should just be Point
+    point: jubjub::ExtendedPoint,
+    // XXX should this just store a PublicKeyBytes?
+    bytes: [u8; 32],
     _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 }
     }
 }
 
@@ -43,7 +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)
+        }
     }
 }
 
diff --git a/src/secret_key.rs b/src/secret_key.rs
index 90df0a2..d9a64dd 100644
--- a/src/secret_key.rs
+++ b/src/secret_key.rs
@@ -1,6 +1,6 @@
 use std::{convert::TryFrom, marker::PhantomData};
 
-use crate::{Binding, Error, PublicKey, Randomizer, SigType, Signature, SpendAuth};
+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.
@@ -29,27 +29,50 @@ 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> {
+        // 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> From<&'a SecretKey<SpendAuth>> for PublicKey<SpendAuth> {
+    fn from(sk: &'a SecretKey<SpendAuth>) -> PublicKey<SpendAuth> {
+        // XXX refactor jubjub API
+        //let basepoint: jubjub::ExtendedPoint = jubjub::AffinePoint::from_bytes(&crate::constants::SPENDAUTHSIG_BASEPOINT_BYTES).unwrap().into();
         unimplemented!();
     }
 }
 
-impl<'a, T: SigType> From<&'a SecretKey<T>> for PublicKey<T> {
-    fn from(sk: &'a SecretKey<T>) -> PublicKey<T> {
+impl<'a> From<&'a SecretKey<Binding>> for PublicKey<Binding> {
+    fn from(sk: &'a SecretKey<Binding>) -> PublicKey<Binding> {
         unimplemented!();
     }
 }