Low 28 Bitcoin Committed Apr 7, 2026 · 11:16 UTC

payment_request: remove "send to" screen

cde7286c View source ↗

Public commit record

What the developer wrote

Authored by Marko Bencun

78/100 · Adequate

payment_request: remove "send to" screen

Redundant with the coin purchase memo info, except for the account
number, but we choose to not show that for better UX. Keypath is still
validated.

The removed tests are redundant with tests of test_validate().

✓ Descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context✓ Mentions testing or verification

The short version

What changed, and why it matters

This commit removes an on-screen confirmation that told users which account would receive funds during a cryptocurrency swap. The remaining screen still shows the amount and destination coin type, but no longer shows the specific account number. The underlying cryptographic keypath validation is still performed, so the technical security check remains. The change is presented by the developer as a user-experience improvement, not as a security fix.

Recommended action

Review whether removing the account-level confirmation materially reduces user ability to detect account-substitution attacks during swaps. If the remaining 'SWAP' screen and keypath validation are considered sufficient, no action is needed; otherwise consider re-adding a non-interactive display of the destination account or a summary screen. Verify that downstream signing paths still enforce the validated keypath.

Security signals we found

UI confirmation step removed from a financial transaction flow

Destination account number no longer displayed to the user

Keypath validation retained according to commit message

Negative tests for missing/short destination derivations removed because the consuming code was removed

No explicit security framing by the vendor in commit or supplied references

Technical analysis

Evidence from the diff

The patch removes the ‘Receive to’ UI confirmation in payment_request.rs for swap/coin-purchase memos. Previously user_verify() parsed the destination amount, derived the destination account number from the address derivation keypath, and prompted the user to confirm ‘Receive to: account #‘. That prompt and its associated parsing/derivation logic are deleted. A parse_coin_purchase_amount() call is moved earlier so the amount format is still validated before the remaining ‘SWAP’ confirmation. The commit message states the removed screen was redundant with the coin-purchase memo info and that the keypath is still validated. Tests are updated to remove expectations of the deleted screen, and several negative tests that checked rejection of malformed/missing destination derivations are removed because the code path they exercised no longer exists.

Changed components

src/rust/bitbox02-rust/src/hww/api/payment_request.rssrc/rust/bitbox02-rust/src/hww/api/bitcoin/signtx.rs (tests only)src/rust/bitbox02-rust/src/hww/api/ethereum/sign.rs (tests only)

Inspect captured patch +19 / −148

diff --git a/src/rust/bitbox02-rust/src/hww/api/bitcoin/signtx.rs b/src/rust/bitbox02-rust/src/hww/api/bitcoin/signtx.rs
index 9804d12..eb534ca 100644
--- a/src/rust/bitbox02-rust/src/hww/api/bitcoin/signtx.rs
+++ b/src/rust/bitbox02-rust/src/hww/api/bitcoin/signtx.rs
@@ -3927,11 +3927,6 @@ mod tests {
                     body: "12.34567890 BTC\nto\n0.25 ETH".into(),
                     longtouch: false,
                 },
-                Screen::Confirm {
-                    title: "Receive to".into(),
-                    body: "ETH account #1".into(),
-                    longtouch: false,
-                },
                 Screen::Recipient {
                     recipient: "bc1q xven xven xven xven xven xven xven xven 2ymj t8".into(),
                     amount: "0.00006000 BTC".into(),
diff --git a/src/rust/bitbox02-rust/src/hww/api/ethereum/sign.rs b/src/rust/bitbox02-rust/src/hww/api/ethereum/sign.rs
index a8e114b..b8513fc 100644
--- a/src/rust/bitbox02-rust/src/hww/api/ethereum/sign.rs
+++ b/src/rust/bitbox02-rust/src/hww/api/ethereum/sign.rs
@@ -1174,11 +1174,6 @@ mod tests {
                 body: "0.530564 ETH\nto\n0.25 ETH".into(),
                 longtouch: false,
             },
-            Screen::Confirm {
-                title: "Receive to".into(),
-                body: "ETH account #1".into(),
-                longtouch: false,
-            },
             Screen::TotalFee {
                 total: "0.53069 ETH".into(),
                 fee: "0.000126 ETH".into(),
@@ -1254,11 +1249,6 @@ mod tests {
                 body: "57 USDT\nto\n0.25 ETH".into(),
                 longtouch: false,
             },
-            Screen::Confirm {
-                title: "Receive to".into(),
-                body: "ETH account #1".into(),
-                longtouch: false,
-            },
             Screen::TotalFee {
                 total: "57 USDT".into(),
                 fee: "0.0012658164 ETH".into(),
diff --git a/src/rust/bitbox02-rust/src/hww/api/payment_request.rs b/src/rust/bitbox02-rust/src/hww/api/payment_request.rs
index 7284710..339b647 100644
--- a/src/rust/bitbox02-rust/src/hww/api/payment_request.rs
+++ b/src/rust/bitbox02-rust/src/hww/api/payment_request.rs
@@ -153,6 +153,7 @@ pub async fn user_verify(
                     "{displayed_source_amount}\nto\n{}",
                     coin_purchase_memo.amount
                 );
+                let _ = parse_coin_purchase_amount(&coin_purchase_memo.amount)?;
                 hal.ui()
                     .confirm(&ConfirmParams {
                         title: "SWAP",
@@ -162,48 +163,6 @@ pub async fn user_verify(
                         ..Default::default()
                     })
                     .await?;
-                let (_, destination_unit) = parse_coin_purchase_amount(&coin_purchase_memo.amount)?;
-                let address_derivation = coin_purchase_memo
-                    .address_derivation
-                    .as_ref()
-                    .ok_or(Error::InvalidInput)?;
-                let destination_account = match address_derivation {
-                    memo::coin_purchase_memo::AddressDerivation::Eth(eth) => {
-                        eth.keypath
-                            .get(2)
-                            .ok_or(Error::InvalidInput)?
-                            .checked_sub(util::bip32::HARDENED)
-                            .ok_or(Error::InvalidInput)?
-                            + 1
-                    }
-                    memo::coin_purchase_memo::AddressDerivation::Btc(btc) => {
-                        if !matches!(
-                            (coin_purchase_memo.coin_type, destination_unit),
-                            (0, "BTC") | (2, "LTC")
-                        ) {
-                            return Err(Error::InvalidInput);
-                        }
-
-                        let script_config =
-                            btc.script_config.as_ref().ok_or(Error::InvalidInput)?;
-
-                        script_config
-                            .keypath
-                            .get(2)
-                            .ok_or(Error::InvalidInput)?
-                            .checked_sub(util::bip32::HARDENED)
-                            .ok_or(Error::InvalidInput)?
-                            + 1
-                    }
-                };
-                hal.ui()
-                    .confirm(&ConfirmParams {
-                        title: "Receive to",
-                        body: &format!("{destination_unit} account #{destination_account}"),
-                        accept_is_nextarrow: true,
-                        ..Default::default()
-                    })
-                    .await?;
             }
             _ => return Err(Error::InvalidInput),
         }
@@ -1447,11 +1406,6 @@ mod tests {
                     body: "0.25000000 BTC\nto\n0.25 ETH".into(),
                     longtouch: false,
                 },
-                Screen::Confirm {
-                    title: "Receive to".into(),
-                    body: "ETH account #1".into(),
-                    longtouch: false,
-                },
             ]
         );
     }
@@ -1501,11 +1455,6 @@ mod tests {
                     body: "0.25000000 BTC\nto\n0.25 LTC".into(),
                     longtouch: false,
                 },
-                Screen::Confirm {
-                    title: "Receive to".into(),
-                    body: "LTC account #1".into(),
-                    longtouch: false,
-                },
             ]
         );
     }
@@ -1614,86 +1563,23 @@ mod tests {
     #[cfg(all(feature = "app-litecoin", feature = "app-ethereum"))]
     #[async_test::test]
     async fn test_user_verify_swap_invalid() {
-        // Invalid swap requests that user_verify must reject because the
-        // UI cannot render them safely.
-        for payment_request in [
-            // Missing destination derivation, so "Receive to" cannot be built.
-            pb::BtcPaymentRequestRequest {
-                recipient_name: "SWAPKIT (Provider)".into(),
-                memos: vec![make_coin_purchase_memo(60, "0.25 ETH", "0x123", None)],
-                nonce: vec![],
-                total_amount: 25000000,
-                signature: vec![],
-            },
-            // Destination keypath is too short to contain an account element.
-            pb::BtcPaymentRequestRequest {
-                recipient_name: "SWAPKIT (Provider)".into(),
-                memos: vec![make_coin_purchase_memo(
-                    60,
-                    "0.25 ETH",
-                    "0x123",
-                    Some(memo::coin_purchase_memo::AddressDerivation::Eth(
-                        memo::coin_purchase_memo::EthAddressDerivation {
-                            keypath: vec![44 + util::bip32::HARDENED, 60 + util::bip32::HARDENED],
-                        },
-                    )),
-                )],
-                nonce: vec![],
-                total_amount: 25000000,
-                signature: vec![],
-            },
-            // BTC-like derivation requires script_config.
-            pb::BtcPaymentRequestRequest {
-                recipient_name: "SWAPKIT (Provider)".into(),
-                memos: vec![make_coin_purchase_memo(
-                    0,
-                    "0.25 BTC",
-                    "bc1qdestination",
-                    Some(memo::coin_purchase_memo::AddressDerivation::Btc(
-                        memo::coin_purchase_memo::BtcAddressDerivation {
-                            script_config: None,
-                        },
-                    )),
-                )],
-                nonce: vec![],
-                total_amount: 25000000,
-                signature: vec![],
-            },
-            // BTC-like destination keypath is too short to contain an account element.
-            pb::BtcPaymentRequestRequest {
-                recipient_name: "SWAPKIT (Provider)".into(),
-                memos: vec![make_coin_purchase_memo(
-                    0,
-                    "0.25 BTC",
-                    "bc1qdestination",
-                    Some(dummy_btc_address_derivation(
-                        pb::btc_script_config::SimpleType::P2wpkh,
-                        &[84 + util::bip32::HARDENED, 0 + util::bip32::HARDENED],
-                    )),
-                )],
-                nonce: vec![],
-                total_amount: 25000000,
-                signature: vec![],
-            },
-            // Display amount must be exactly "<positive-decimal> <unit>".
-            pb::BtcPaymentRequestRequest {
-                recipient_name: "SWAPKIT (Provider)".into(),
-                memos: vec![make_coin_purchase_memo(
-                    60,
-                    "foo bar baz",
-                    "0x123",
-                    Some(dummy_eth_address_derivation(/*valid=*/ true)),
-                )],
-                nonce: vec![],
-                total_amount: 25000000,
-                signature: vec![],
-            },
-        ] {
-            let mut mock_hal = TestingHal::new();
-            assert_eq!(
-                user_verify(&mut mock_hal, &payment_request, "0.25000000 BTC",).await,
-                Err(Error::InvalidInput)
-            );
-        }
+        // Display amount must be exactly "<positive-decimal> <unit>".
+        let payment_request = pb::BtcPaymentRequestRequest {
+            recipient_name: "SWAPKIT (Provider)".into(),
+            memos: vec![make_coin_purchase_memo(
+                60,
+                "foo bar baz",
+                "0x123",
+                Some(dummy_eth_address_derivation(/*valid=*/ true)),
+            )],
+            nonce: vec![],
+            total_amount: 25000000,
+            signature: vec![],
+        };
+        let mut mock_hal = TestingHal::new();
+        assert_eq!(
+            user_verify(&mut mock_hal, &payment_request, "0.25000000 BTC",).await,
+            Err(Error::InvalidInput),
+        );
     }
 }

Risk score

Why this scored 28/100

Our methodology →

Potential impact 5/30

Exploitability 5/25

Stealth signal 5/15

Affected reach 5/15

Confidence 5/10

Evidence quality 3/5

Human-validated context

Community notes

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What the developer wrote

What changed, and why it matters

Security signals we found

Evidence from the diff

Changed components

Why this scored 28/100

Community notes

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