From a93e2db44b26806c5dd3070189bccb01063e846c Mon Sep 17 00:00:00 2001
From: Deirdre Connolly <deirdre@zfnd.org>
Date: Mon, 27 Jan 2020 23:25:17 -0500
Subject: [PATCH] Add and use OutCiphertext

Instead of [u64; 10].
---
 zebra-chain/src/transaction/serialize.rs     | 27 +-------
 zebra-chain/src/transaction/shielded_data.rs | 68 ++++++++++++++++++--
 2 files changed, 67 insertions(+), 28 deletions(-)

diff --git a/zebra-chain/src/transaction/serialize.rs b/zebra-chain/src/transaction/serialize.rs
index b54580d3..8c204947 100644
--- a/zebra-chain/src/transaction/serialize.rs
+++ b/zebra-chain/src/transaction/serialize.rs
@@ -2,7 +2,7 @@
 //! transaction types, so that all of the serialization logic is in one place.
 
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
-use std::io::{self, Read};
+use std::io;
 
 use crate::proofs::ZkSnarkProof;
 use crate::serialization::{
@@ -177,21 +177,8 @@ impl ZcashSerialize for OutputDescription {
         writer.write_all(&self.cv[..])?;
         writer.write_all(&self.cmu[..])?;
         writer.write_all(&self.ephemeral_key[..])?;
-        // assert_eq!(self.enc_ciphertext.len(), 580);
         self.enc_ciphertext.zcash_serialize(&mut writer)?;
-        // XXX remove this assertion when types are refined
-        assert_eq!(self.out_ciphertext.len(), 80);
-        // XXX very ugly, this happens because we used a [u64; 10] instead of
-        // [u8; 80] to get trait impls and it will disappear when we refine to
-        // a note ciphertext type
-        writer.write_all(
-            &{
-                use byteorder::ByteOrder;
-                let mut bytes = [0u8; 80];
-                LittleEndian::write_u64_into(&self.out_ciphertext[..], &mut bytes);
-                bytes
-            }[..],
-        )?;
+        self.out_ciphertext.zcash_serialize(&mut writer)?;
         self.zkproof.zcash_serialize(&mut writer)?;
         Ok(())
     }
@@ -204,15 +191,7 @@ impl ZcashDeserialize for OutputDescription {
             cmu: reader.read_32_bytes()?,
             ephemeral_key: reader.read_32_bytes()?,
             enc_ciphertext: shielded_data::EncryptedCiphertext::zcash_deserialize(&mut reader)?,
-            out_ciphertext: {
-                // XXX this is horrible, see above, will be removed with type refinement
-                use byteorder::ByteOrder;
-                let mut bytes = [0u8; 80];
-                reader.read_exact(&mut bytes[..])?;
-                let mut u64s = [0u64; 10];
-                LittleEndian::read_u64_into(&bytes, &mut u64s[..]);
-                u64s
-            },
+            out_ciphertext: shielded_data::OutCiphertext::zcash_deserialize(&mut reader)?,
             zkproof: Groth16Proof::zcash_deserialize(&mut reader)?,
         })
     }
diff --git a/zebra-chain/src/transaction/shielded_data.rs b/zebra-chain/src/transaction/shielded_data.rs
index 82a7b37a..deb4c565 100644
--- a/zebra-chain/src/transaction/shielded_data.rs
+++ b/zebra-chain/src/transaction/shielded_data.rs
@@ -91,10 +91,7 @@ pub struct OutputDescription {
     /// A ciphertext component for the encrypted output note.
     pub enc_ciphertext: EncryptedCiphertext,
     /// A ciphertext component for the encrypted output note.
-    ///
-    /// XXX refine to a specific type.
-    /// XXX this is a [u64; 10] rather than a [u8; 80] to get trait impls
-    pub out_ciphertext: [u64; 10],
+    pub out_ciphertext: OutCiphertext,
     /// The ZK output proof.
     pub zkproof: Groth16Proof,
 }
@@ -267,3 +264,66 @@ impl Arbitrary for EncryptedCiphertext {
 
     type Strategy = BoxedStrategy<Self>;
 }
+
+/// A ciphertext component for encrypted output notes.
+pub struct OutCiphertext(pub [u8; 80]);
+
+impl fmt::Debug for OutCiphertext {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("OutCiphertext")
+            .field(&hex::encode(&self.0[..]))
+            .finish()
+    }
+}
+
+// These impls all only exist because of array length restrictions.
+
+impl Copy for OutCiphertext {}
+
+impl Clone for OutCiphertext {
+    fn clone(&self) -> Self {
+        let mut bytes = [0; 80];
+        bytes[..].copy_from_slice(&self.0[..]);
+        Self(bytes)
+    }
+}
+
+impl PartialEq for OutCiphertext {
+    fn eq(&self, other: &Self) -> bool {
+        self.0[..] == other.0[..]
+    }
+}
+
+impl Eq for OutCiphertext {}
+
+impl ZcashSerialize for OutCiphertext {
+    fn zcash_serialize<W: io::Write>(&self, mut writer: W) -> Result<(), SerializationError> {
+        writer.write_all(&self.0[..])?;
+        Ok(())
+    }
+}
+
+impl ZcashDeserialize for OutCiphertext {
+    fn zcash_deserialize<R: io::Read>(mut reader: R) -> Result<Self, SerializationError> {
+        let mut bytes = [0; 80];
+        reader.read_exact(&mut bytes[..])?;
+        Ok(Self(bytes))
+    }
+}
+
+#[cfg(test)]
+impl Arbitrary for OutCiphertext {
+    type Parameters = ();
+
+    fn arbitrary_with(_args: Self::Parameters) -> Self::Strategy {
+        (vec(any::<u8>(), 80))
+            .prop_map(|v| {
+                let mut bytes = [0; 80];
+                bytes.copy_from_slice(v.as_slice());
+                return Self(bytes);
+            })
+            .boxed()
+    }
+
+    type Strategy = BoxedStrategy<Self>;
+}