Move amount_decryption into EncryptedAmount::decrypt

coins/monero/src/ringct/bulletproofs/mod.rs

@@ -189,7 +189,7 @@ impl Bulletproof {
     self.write_core(w, |points, w| write_vec(write_point, points, w))
   }
 
-  /// Serialize the Bulletproof(+) to a Vec<u8>.
+  /// Serialize the Bulletproof(+) to a `Vec<u8>`.
   pub fn serialize(&self) -> Vec<u8> {
     let mut serialized = vec![];
     self.write(&mut serialized).unwrap();

coins/monero/src/wallet/mod.rs

@@ -10,7 +10,7 @@ use curve25519_dalek::{
 };
 
 use crate::{
-  hash, hash_to_scalar, serialize::write_varint, ringct::EncryptedAmount, transaction::Input,
+  hash, hash_to_scalar, serialize::write_varint, Commitment, ringct::EncryptedAmount, transaction::Input,
 };
 
 pub mod extra;
@@ -94,15 +94,20 @@ pub(crate) fn commitment_mask(shared_key: Scalar) -> Scalar {
   hash_to_scalar(&mask)
 }
 
-pub(crate) fn amount_encryption(amount: u64, key: Scalar) -> [u8; 8] {
+pub(crate) fn compact_amount_encryption(amount: u64, key: Scalar) -> [u8; 8] {
   let mut amount_mask = b"amount".to_vec();
   amount_mask.extend(key.to_bytes());
   (amount ^ u64::from_le_bytes(hash(&amount_mask)[.. 8].try_into().unwrap())).to_le_bytes()
 }
 
-// TODO: Move this under EncryptedAmount?
-fn amount_decryption(amount: &EncryptedAmount, key: Scalar) -> (Scalar, u64) {
-  match amount {
+impl EncryptedAmount {
+  /// Decrypt an EncryptedAmount into the Commitment it encrypts.
+  ///
+  /// The caller must verify the decrypted Commitment matches with the actual Commitment used
+  /// within in the Monero protocol.
+  pub fn decrypt(&self, key: Scalar) -> Commitment {
+    match self {
+      // TODO: Add a test vector for this
       EncryptedAmount::Original { mask, amount } => {
         let mask_shared_sec = hash(key.as_bytes());
         let mask =
@@ -114,14 +119,15 @@ fn amount_decryption(amount: &EncryptedAmount, key: Scalar) -> (Scalar, u64) {
         // d2b from rctTypes.cpp
         let amount = u64::from_le_bytes(amount_scalar.to_bytes()[0 .. 8].try_into().unwrap());
 
-      (mask, amount)
+        Commitment::new(mask, amount)
       }
-    EncryptedAmount::Compact { amount } => (
+      EncryptedAmount::Compact { amount } => Commitment::new(
         commitment_mask(key),
-      u64::from_le_bytes(amount_encryption(u64::from_le_bytes(*amount), key)),
+        u64::from_le_bytes(compact_amount_encryption(u64::from_le_bytes(*amount), key)),
       ),
     }
   }
+}
 
 /// The private view key and public spend key, enabling scanning transactions.
 #[derive(Clone, Zeroize, ZeroizeOnDrop)]

coins/monero/src/wallet/scan.rs

@@ -17,9 +17,7 @@ use crate::{
   transaction::{Input, Timelock, Transaction},
   block::Block,
   rpc::{RpcError, RpcConnection, Rpc},
-  wallet::{
-    PaymentId, Extra, address::SubaddressIndex, Scanner, uniqueness, shared_key, amount_decryption,
-  },
+  wallet::{PaymentId, Extra, address::SubaddressIndex, Scanner, uniqueness, shared_key},
 };
 
 /// An absolute output ID, defined as its transaction hash and output index.
@@ -427,15 +425,13 @@ impl Scanner {
           commitment.amount = amount;
         // Regular transaction
         } else {
-          let (mask, amount) = match tx.rct_signatures.base.encrypted_amounts.get(o) {
-            Some(amount) => amount_decryption(amount, shared_key),
+          commitment = match tx.rct_signatures.base.encrypted_amounts.get(o) {
+            Some(amount) => amount.decrypt(shared_key),
             // This should never happen, yet it may be possible with miner transactions?
             // Using get just decreases the possibility of a panic and lets us move on in that case
             None => break,
           };
 
-          // Rebuild the commitment to verify it
-          commitment = Commitment::new(mask, amount);
           // If this is a malicious commitment, move to the next output
           // Any other R value will calculate to a different spend key and are therefore ignorable
           if Some(&commitment.calculate()) != tx.rct_signatures.base.commitments.get(o) {

coins/monero/src/wallet/send/mod.rs

@@ -39,7 +39,7 @@ use crate::{
   wallet::{
     address::{Network, AddressSpec, MoneroAddress},
     ViewPair, SpendableOutput, Decoys, PaymentId, ExtraField, Extra, key_image_sort, uniqueness,
-    shared_key, commitment_mask, amount_encryption,
+    shared_key, commitment_mask, compact_amount_encryption,
     extra::{ARBITRARY_DATA_MARKER, MAX_ARBITRARY_DATA_SIZE},
   },
 };
@@ -92,7 +92,7 @@ impl SendOutput {
         view_tag,
         dest: ((&shared_key * ED25519_BASEPOINT_TABLE) + output.0.spend),
         commitment: Commitment::new(commitment_mask(shared_key), output.1),
-        amount: amount_encryption(output.1, shared_key),
+        amount: compact_amount_encryption(output.1, shared_key),
       },
       payment_id,
     )
@@ -936,7 +936,7 @@ impl Eventuality {
       return false;
     }
 
-    // TODO: Remove this when the following for loop is updated
+    // TODO: Remove this if/when the following for loop is updated to support older TXs
     assert!(
       rct_type.compact_encrypted_amounts(),
       "created an Eventuality for a very old RctType we don't support proving for"