[zk-token-sdk] Define FeeEncryption as a wrapper around `GroupedElG…

…amalCiphertext` (#32144)

* define `FeeEncryption` as a wrapper around `GroupedElGamalCiphertext`

* define pod `FeeEncryption` as a wrapper around `GroupedElGamalCiphertext2Handles`

* update proof data computation

* add comments about unwraps

(cherry picked from commit 37f51e8)

zk-token-sdk/src/instruction/transfer/encryption.rs

@@ -1,11 +1,8 @@
 #[cfg(not(target_os = "solana"))]
-use crate::{
-    encryption::{
-        elgamal::{DecryptHandle, ElGamalPubkey},
-        grouped_elgamal::{GroupedElGamal, GroupedElGamalCiphertext},
-        pedersen::{Pedersen, PedersenCommitment, PedersenOpening},
-    },
-    zk_token_elgamal::pod,
+use crate::encryption::{
+    elgamal::{DecryptHandle, ElGamalPubkey},
+    grouped_elgamal::{GroupedElGamal, GroupedElGamalCiphertext},
+    pedersen::{PedersenCommitment, PedersenOpening},
 };
 
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
@@ -54,15 +51,10 @@ impl TransferAmountCiphertext {
     }
 }
 
-// FeeEncryption
-#[derive(Clone)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 #[repr(C)]
 #[cfg(not(target_os = "solana"))]
-pub struct FeeEncryption {
-    pub commitment: PedersenCommitment,
-    pub destination_handle: DecryptHandle,
-    pub withdraw_withheld_authority_handle: DecryptHandle,
-}
+pub struct FeeEncryption(pub(crate) GroupedElGamalCiphertext<2>);
 
 #[cfg(not(target_os = "solana"))]
 impl FeeEncryption {
@@ -71,22 +63,29 @@ impl FeeEncryption {
         destination_pubkey: &ElGamalPubkey,
         withdraw_withheld_authority_pubkey: &ElGamalPubkey,
     ) -> (Self, PedersenOpening) {
-        let (commitment, opening) = Pedersen::new(amount);
-        let fee_encryption = Self {
-            commitment,
-            destination_handle: destination_pubkey.decrypt_handle(&opening),
-            withdraw_withheld_authority_handle: withdraw_withheld_authority_pubkey
-                .decrypt_handle(&opening),
-        };
+        let opening = PedersenOpening::new_rand();
+        let grouped_ciphertext = GroupedElGamal::<2>::encrypt_with(
+            [destination_pubkey, withdraw_withheld_authority_pubkey],
+            amount,
+            &opening,
+        );
+
+        (Self(grouped_ciphertext), opening)
+    }
+
+    pub fn get_commitment(&self) -> &PedersenCommitment {
+        &self.0.commitment
+    }
 
-        (fee_encryption, opening)
+    pub fn get_destination_handle(&self) -> &DecryptHandle {
+        // `FeeEncryption` is a wrapper for `GroupedElGamalCiphertext<2>`, which holds
+        // exactly two decryption handles.
+        self.0.handles.get(0).unwrap()
     }
 
-    pub fn to_pod(&self) -> pod::FeeEncryption {
-        pod::FeeEncryption {
-            commitment: self.commitment.into(),
-            destination_handle: self.destination_handle.into(),
-            withdraw_withheld_authority_handle: self.withdraw_withheld_authority_handle.into(),
-        }
+    pub fn get_withdraw_withheld_authority_handle(&self) -> &DecryptHandle {
+        // `FeeEncryption` is a wrapper for `GroupedElGamalCiphertext<2>`, which holds
+        // exactly two decryption handles.
+        self.0.handles.get(1).unwrap()
     }
 }

zk-token-sdk/src/instruction/transfer/with_fee.rs

@@ -186,8 +186,8 @@ impl TransferWithFeeData {
         let pod_ciphertext_lo: pod::TransferAmountCiphertext = ciphertext_lo.into();
         let pod_ciphertext_hi: pod::TransferAmountCiphertext = ciphertext_hi.into();
         let pod_new_source_ciphertext: pod::ElGamalCiphertext = new_source_ciphertext.into();
-        let pod_fee_ciphertext_lo: pod::FeeEncryption = fee_ciphertext_lo.to_pod();
-        let pod_fee_ciphertext_hi: pod::FeeEncryption = fee_ciphertext_hi.to_pod();
+        let pod_fee_ciphertext_lo: pod::FeeEncryption = fee_ciphertext_lo.into();
+        let pod_fee_ciphertext_hi: pod::FeeEncryption = fee_ciphertext_hi.into();
 
         let context = TransferWithFeeProofContext {
             ciphertext_lo: pod_ciphertext_lo,
@@ -266,17 +266,17 @@ impl TransferWithFeeData {
 
         let fee_handle_lo = match role {
             Role::Source => None,
-            Role::Destination => Some(fee_ciphertext_lo.destination_handle),
+            Role::Destination => Some(fee_ciphertext_lo.get_destination_handle()),
             Role::Auditor => None,
             Role::WithdrawWithheldAuthority => {
-                Some(fee_ciphertext_lo.withdraw_withheld_authority_handle)
+                Some(fee_ciphertext_lo.get_withdraw_withheld_authority_handle())
             }
         };
 
         if let Some(handle) = fee_handle_lo {
             Ok(ElGamalCiphertext {
-                commitment: fee_ciphertext_lo.commitment,
-                handle,
+                commitment: *fee_ciphertext_lo.get_commitment(),
+                handle: *handle,
             })
         } else {
             Err(ProofError::MissingCiphertext)
@@ -289,17 +289,17 @@ impl TransferWithFeeData {
 
         let fee_handle_hi = match role {
             Role::Source => None,
-            Role::Destination => Some(fee_ciphertext_hi.destination_handle),
+            Role::Destination => Some(fee_ciphertext_hi.get_destination_handle()),
             Role::Auditor => None,
             Role::WithdrawWithheldAuthority => {
-                Some(fee_ciphertext_hi.withdraw_withheld_authority_handle)
+                Some(fee_ciphertext_hi.get_withdraw_withheld_authority_handle())
             }
         };
 
         if let Some(handle) = fee_handle_hi {
             Ok(ElGamalCiphertext {
-                commitment: fee_ciphertext_hi.commitment,
-                handle,
+                commitment: *fee_ciphertext_hi.get_commitment(),
+                handle: *handle,
             })
         } else {
             Err(ProofError::MissingCiphertext)
@@ -467,8 +467,8 @@ impl TransferWithFeeProof {
         let combined_fee_amount =
             combine_lo_hi_u64(fee_amount_lo, fee_amount_hi, TRANSFER_AMOUNT_LO_BITS);
         let combined_fee_commitment = combine_lo_hi_commitments(
-            &fee_ciphertext_lo.commitment,
-            &fee_ciphertext_hi.commitment,
+            fee_ciphertext_lo.get_commitment(),
+            fee_ciphertext_hi.get_commitment(),
             TRANSFER_AMOUNT_LO_BITS,
         );
         let combined_fee_opening =
@@ -611,8 +611,8 @@ impl TransferWithFeeProof {
             TRANSFER_AMOUNT_LO_BITS,
         );
         let combined_fee_commitment = combine_lo_hi_commitments(
-            &fee_ciphertext_lo.commitment,
-            &fee_ciphertext_hi.commitment,
+            fee_ciphertext_lo.get_commitment(),
+            fee_ciphertext_hi.get_commitment(),
             TRANSFER_AMOUNT_LO_BITS,
         );
 
@@ -640,14 +640,17 @@ impl TransferWithFeeProof {
                 &transfer_with_fee_pubkeys.destination_pubkey,
                 &transfer_with_fee_pubkeys.withdraw_withheld_authority_pubkey,
             ),
-            (&fee_ciphertext_lo.commitment, &fee_ciphertext_hi.commitment),
             (
-                &fee_ciphertext_lo.destination_handle,
-                &fee_ciphertext_hi.destination_handle,
+                fee_ciphertext_lo.get_commitment(),
+                fee_ciphertext_hi.get_commitment(),
+            ),
+            (
+                fee_ciphertext_lo.get_destination_handle(),
+                fee_ciphertext_hi.get_destination_handle(),
             ),
             (
-                &fee_ciphertext_lo.withdraw_withheld_authority_handle,
-                &fee_ciphertext_hi.withdraw_withheld_authority_handle,
+                fee_ciphertext_lo.get_withdraw_withheld_authority_handle(),
+                fee_ciphertext_hi.get_withdraw_withheld_authority_handle(),
             ),
             transcript,
         )?;
@@ -663,8 +666,8 @@ impl TransferWithFeeProof {
                 ciphertext_hi.get_commitment(),
                 &claimed_commitment,
                 &claimed_commitment_negated,
-                &fee_ciphertext_lo.commitment,
-                &fee_ciphertext_hi.commitment,
+                fee_ciphertext_lo.get_commitment(),
+                fee_ciphertext_hi.get_commitment(),
             ],
             vec![
                 TRANSFER_SOURCE_AMOUNT_BITS, // 64

zk-token-sdk/src/zk_token_elgamal/convert.rs

@@ -53,9 +53,7 @@ mod target_arch {
         crate::{
             curve25519::scalar::PodScalar,
             errors::ProofError,
-            instruction::transfer::{
-                FeeEncryption, FeeParameters, TransferPubkeys, TransferWithFeePubkeys,
-            },
+            instruction::transfer::{FeeParameters, TransferPubkeys, TransferWithFeePubkeys},
         },
         curve25519_dalek::{ristretto::CompressedRistretto, scalar::Scalar},
         std::convert::TryFrom,
@@ -135,32 +133,6 @@ mod target_arch {
         }
     }
 
-    impl From<FeeEncryption> for pod::FeeEncryption {
-        fn from(ciphertext: FeeEncryption) -> Self {
-            Self {
-                commitment: ciphertext.commitment.into(),
-                destination_handle: ciphertext.destination_handle.into(),
-                withdraw_withheld_authority_handle: ciphertext
-                    .withdraw_withheld_authority_handle
-                    .into(),
-            }
-        }
-    }
-
-    impl TryFrom<pod::FeeEncryption> for FeeEncryption {
-        type Error = ProofError;
-
-        fn try_from(pod: pod::FeeEncryption) -> Result<Self, Self::Error> {
-            Ok(Self {
-                commitment: pod.commitment.try_into()?,
-                destination_handle: pod.destination_handle.try_into()?,
-                withdraw_withheld_authority_handle: pod
-                    .withdraw_withheld_authority_handle
-                    .try_into()?,
-            })
-        }
-    }
-
     impl From<FeeParameters> for pod::FeeParameters {
         fn from(parameters: FeeParameters) -> Self {
             Self {

zk-token-sdk/src/zk_token_elgamal/pod/instruction.rs

@@ -1,6 +1,6 @@
 use crate::zk_token_elgamal::pod::{
-    DecryptHandle, ElGamalPubkey, GroupedElGamalCiphertext3Handles, PedersenCommitment, Pod,
-    PodU16, PodU64, Zeroable,
+    ElGamalPubkey, GroupedElGamalCiphertext2Handles, GroupedElGamalCiphertext3Handles, Pod, PodU16,
+    PodU64, Zeroable,
 };
 #[cfg(not(target_os = "solana"))]
 use crate::{errors::ProofError, instruction::transfer as decoded};
@@ -44,10 +44,22 @@ impl TryFrom<TransferAmountCiphertext> for decoded::TransferAmountCiphertext {
 
 #[derive(Clone, Copy, Pod, Zeroable)]
 #[repr(C)]
-pub struct FeeEncryption {
-    pub commitment: PedersenCommitment,
-    pub destination_handle: DecryptHandle,
-    pub withdraw_withheld_authority_handle: DecryptHandle,
+pub struct FeeEncryption(pub GroupedElGamalCiphertext2Handles);
+
+#[cfg(not(target_os = "solana"))]
+impl From<decoded::FeeEncryption> for FeeEncryption {
+    fn from(decoded_ciphertext: decoded::FeeEncryption) -> Self {
+        Self(decoded_ciphertext.0.into())
+    }
+}
+
+#[cfg(not(target_os = "solana"))]
+impl TryFrom<FeeEncryption> for decoded::FeeEncryption {
+    type Error = ProofError;
+
+    fn try_from(pod_ciphertext: FeeEncryption) -> Result<Self, Self::Error> {
+        Ok(Self(pod_ciphertext.0.try_into()?))
+    }
 }
 
 #[derive(Clone, Copy, Pod, Zeroable)]