add constructor from bytes

src/dhke.rs

@@ -12,13 +12,14 @@
 use core::ops::Mul;
 
 use subtle::{Choice, ConstantTimeEq};
+use tari_utilities::ByteArrayError;
 use zeroize::{Zeroize, ZeroizeOnDrop};
 
 use crate::keys::PublicKey;
 
 /// The result of a Diffie-Hellman key exchange
 #[derive(PartialEq, Eq, Zeroize, ZeroizeOnDrop)]
-pub struct DiffieHellmanSharedSecret<P>(pub P)
+pub struct DiffieHellmanSharedSecret<P>(P)
 where P: PublicKey;
 
 impl<P> DiffieHellmanSharedSecret<P>
@@ -31,6 +32,12 @@ where
         Self(sk * pk)
     }
 
+    // Constructs a new Diffie-Hellman key exchange from an already created Diffie-Hellman key exchange
+    pub fn from_canonical_bytes(bytes: &[u8]) -> Result<Self, ByteArrayError> {
+        let pk = P::from_canonical_bytes(bytes)?;
+        Ok(Self(pk))
+    }
+
     /// Get the shared secret as a byte array
     pub fn as_bytes(&self) -> &[u8] {
         self.0.as_bytes()
@@ -71,5 +78,9 @@ mod test {
         let right = DiffieHellmanSharedSecret::<RistrettoPublicKey>::new(&sk2, &pk1);
 
         assert_eq!(left.as_bytes(), right.as_bytes());
+
+        let left_bytes = left.as_bytes();
+        let new_left = DiffieHellmanSharedSecret::<RistrettoPublicKey>::from_canonical_bytes(left_bytes).unwrap();
+        assert_eq!(left.as_bytes(), new_left.as_bytes());
     }
 }