From c150b4b197ec1bea65cbc5cbbb61a90341ba0c8e Mon Sep 17 00:00:00 2001
From: Sam Kim <skim13@cs.stanford.edu>
Date: Tue, 5 Oct 2021 09:14:04 -0400
Subject: [PATCH] Replace to_elgamal_ciphertext with From trait for
 ElGamalCiphertext

---
 zk-token-sdk/src/encryption/elgamal.rs   | 15 ++++++++++++---
 zk-token-sdk/src/encryption/pedersen.rs  | 20 +++++---------------
 zk-token-sdk/src/instruction/transfer.rs |  4 ++--
 3 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/zk-token-sdk/src/encryption/elgamal.rs b/zk-token-sdk/src/encryption/elgamal.rs
index dfdc7852f..f07b633a9 100644
--- a/zk-token-sdk/src/encryption/elgamal.rs
+++ b/zk-token-sdk/src/encryption/elgamal.rs
@@ -154,7 +154,7 @@ impl ElGamalPubkey {
     /// Generate a decryption token from an ElGamal public key and a Pedersen
     /// opening.
     pub fn gen_decrypt_handle(self, open: &PedersenOpening) -> PedersenDecryptHandle {
-        PedersenDecryptHandle::generate_handle(open, &self)
+        PedersenDecryptHandle::new(&self, open)
     }
 }
 
@@ -288,6 +288,15 @@ impl ElGamalCiphertext {
     }
 }
 
+impl From<(PedersenCommitment, PedersenDecryptHandle)> for ElGamalCiphertext {
+    fn from((comm, handle): (PedersenCommitment, PedersenDecryptHandle)) -> Self {
+        ElGamalCiphertext {
+            message_comm: comm,
+            decrypt_handle: handle,
+        }
+    }
+}
+
 impl<'a, 'b> Add<&'b ElGamalCiphertext> for &'a ElGamalCiphertext {
     type Output = ElGamalCiphertext;
 
@@ -389,8 +398,8 @@ mod tests {
         let decrypt_handle_1 = pk_1.gen_decrypt_handle(&open);
         let decrypt_handle_2 = pk_2.gen_decrypt_handle(&open);
 
-        let ct_1 = decrypt_handle_1.to_elgamal_ciphertext(comm);
-        let ct_2 = decrypt_handle_2.to_elgamal_ciphertext(comm);
+        let ct_1: ElGamalCiphertext = (comm, decrypt_handle_1).into();
+        let ct_2: ElGamalCiphertext = (comm, decrypt_handle_2).into();
 
         let expected_instance = DiscreteLog {
             generator: PedersenBase::default().G,
diff --git a/zk-token-sdk/src/encryption/pedersen.rs b/zk-token-sdk/src/encryption/pedersen.rs
index 47f077520..462e9ae8b 100644
--- a/zk-token-sdk/src/encryption/pedersen.rs
+++ b/zk-token-sdk/src/encryption/pedersen.rs
@@ -1,7 +1,7 @@
 #[cfg(not(target_arch = "bpf"))]
 use rand::{rngs::OsRng, CryptoRng, RngCore};
 use {
-    crate::encryption::elgamal::{ElGamalCiphertext, ElGamalPubkey},
+    crate::encryption::elgamal::ElGamalPubkey,
     core::ops::{Add, Div, Mul, Sub},
     curve25519_dalek::{
         constants::{RISTRETTO_BASEPOINT_COMPRESSED, RISTRETTO_BASEPOINT_POINT},
@@ -47,8 +47,6 @@ pub struct Pedersen;
 impl Pedersen {
     /// Given a number as input, the function returns a Pedersen commitment of
     /// the number and its corresponding opening.
-    ///
-    /// TODO: Interface that takes a random generator as input
     #[cfg(not(target_arch = "bpf"))]
     #[allow(clippy::new_ret_no_self)]
     pub fn new<T: Into<Scalar>>(amount: T) -> (PedersenCommitment, PedersenOpening) {
@@ -255,22 +253,14 @@ define_div_variants!(
 #[derive(Serialize, Deserialize, Default, Clone, Copy, Debug, Eq, PartialEq)]
 pub struct PedersenDecryptHandle(pub(crate) RistrettoPoint);
 impl PedersenDecryptHandle {
+    pub fn new(pk: &ElGamalPubkey, open: &PedersenOpening) -> Self {
+        Self(pk.get_point() * open.get_scalar())
+    }
+
     pub fn get_point(&self) -> RistrettoPoint {
         self.0
     }
 
-    pub fn generate_handle(open: &PedersenOpening, pk: &ElGamalPubkey) -> PedersenDecryptHandle {
-        PedersenDecryptHandle(open.get_scalar() * pk.get_point())
-    }
-
-    /// Maps a decryption token and Pedersen commitment to ElGamal ciphertext
-    pub fn to_elgamal_ciphertext(self, comm: PedersenCommitment) -> ElGamalCiphertext {
-        ElGamalCiphertext {
-            message_comm: comm,
-            decrypt_handle: self,
-        }
-    }
-
     #[allow(clippy::wrong_self_convention)]
     pub fn to_bytes(&self) -> [u8; 32] {
         self.0.compress().to_bytes()
diff --git a/zk-token-sdk/src/instruction/transfer.rs b/zk-token-sdk/src/instruction/transfer.rs
index 6e9fa029a..4307be7da 100644
--- a/zk-token-sdk/src/instruction/transfer.rs
+++ b/zk-token-sdk/src/instruction/transfer.rs
@@ -157,7 +157,7 @@ impl TransferData {
             .try_into()?;
         let decryption_handle = combine_u32_handles(decryption_handle_lo, decryption_handle_hi);
 
-        Ok(decryption_handle.to_elgamal_ciphertext(transfer_comm))
+        Ok((transfer_comm, decryption_handle).into())
     }
 
     /// Extracts the lo and hi destination ciphertexts associated with a transfer data and returns
@@ -173,7 +173,7 @@ impl TransferData {
             self.validity_proof.decryption_handles_hi.dest.try_into()?;
         let decryption_handle = combine_u32_handles(decryption_handle_lo, decryption_handle_hi);
 
-        Ok(decryption_handle.to_elgamal_ciphertext(transfer_comm))
+        Ok((transfer_comm, decryption_handle).into())
     }
 }