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fix(tempo): always bind payments to the challenge memo #28

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fix(tempo): always bind payments to the challenge memo #28

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15 changes: 7 additions & 8 deletions src/main/java/com/stripe/mpp/methods/tempo/TempoChargeIntent.java
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Original file line number Diff line number Diff line change
Expand Up @@ -29,11 +29,12 @@
* </ul>
*
* <p>A qualifying Transfer of the requested token, recipient and amount is not
* enough. Unless the merchant set an explicit memo, the matched logs must include
* a {@code TransferWithMemo} whose memo is bound to this challenge (MPP attribution
* tag, server fingerprint of the challenge realm, and nonce
* {@code keccak256(challengeId)[0..6]}). That is what stops a third party from
* presenting someone else's settled transaction as their own payment.
* enough. The matched logs must include a {@code TransferWithMemo} whose memo
* is bound to this challenge (MPP attribution tag, server fingerprint of the
* challenge realm, and nonce {@code keccak256(challengeId)[0..6]}). A merchant
* memo, when present, is an additional exact-match constraint — it does not
* skip that binding. That is what stops a third party from presenting someone
* else's settled transaction as their own payment.
*
* <p>Create the intent once and reuse it so its replay store is shared across requests:
*
Expand Down Expand Up @@ -159,9 +160,7 @@ private Receipt awaitReceipt(
"transaction logs contain no Transfer matching the request currency, recipient, and amount"
);
}
if (memoFrom(request) == null) {
assertChallengeBoundMemo(matched, credential);
}
assertChallengeBoundMemo(matched, credential);
return Receipt.success(txHash, "tempo");
}
if (i < maxRetries - 1) {
Expand Down
11 changes: 6 additions & 5 deletions src/main/java/com/stripe/mpp/methods/tempo/TempoMethod.java
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Expand Up @@ -104,12 +104,13 @@ public Builder store(Store store) {
}

/**
* Sets an explicit TIP-20 memo that payments must match.
* Sets an explicit TIP-20 memo that payments must match in addition to
* the challenge-bound MPP attribution memo.
*
* <p>When omitted, clients write an MPP attribution memo bound to the
* challenge and the server requires that binding. An explicit memo is
* matched exactly and is not challenge-bound — the caller must make it
* unique per challenge if hash reuse across challenges should be rejected.
* <p>Verification always requires an on-chain memo bound to the
* challenge id and realm. A method-wide static value cannot satisfy
* that binding across distinct challenges, so omit this unless the
* advertised memo is itself unique per challenge.
*/
public Builder memo(String memo) {
this.memo = Objects.requireNonNull(memo, "memo");
Expand Down
81 changes: 67 additions & 14 deletions src/test/java/com/stripe/mpp/methods/tempo/TempoChargeIntentTest.java
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Expand Up @@ -49,13 +49,17 @@ static Credential txCredential(String rawTx) {
}

static Credential hashCredential(String txHash) {
return hashCredential(txHash, null);
return hashCredential(txHash, (String) null);
}

static Credential hashCredential(String txHash, String source) {
return new Credential(ECHO, Map.of("type", "hash", "hash", txHash), source);
}

static Credential hashCredential(String txHash, ChallengeEcho echo) {
return new Credential(echo, Map.of("type", "hash", "hash", txHash), null);
}

static String didPkh(int chainId, String address) {
return "did:pkh:eip155:" + chainId + ":" + address;
}
Expand Down Expand Up @@ -370,44 +374,43 @@ void pushAcceptsChallengeBoundMemoAlongsideAPlainTransfer() {

@Test
void explicitMemoMustMatchExactly() {
String merchantMemo = "0x" + "ab".repeat(32);
Map<String, Object> request = new HashMap<>(REQUEST);
request.put("memo", merchantMemo);
request.put("memo", BOUND_MEMO);

Receipt result = intent(new StubRpc(null,
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, merchantMemo), 0))
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, BOUND_MEMO), 0))
.verify(hashCredential("0xpushedtx"), request);
assertThat(result.status()).isEqualTo("success");
}

@Test
void explicitMemoMismatchIsRejected() {
String merchantMemo = "0x" + "ab".repeat(32);
String otherMemo = "0x" + "cd".repeat(32);
Map<String, Object> request = new HashMap<>(REQUEST);
request.put("memo", merchantMemo);

assertThatThrownBy(() -> intent(new StubRpc(null,
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, otherMemo), 0))
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, BOUND_MEMO), 0))
.verify(hashCredential("0xpushedtx"), request))
.isInstanceOf(VerificationFailedException.class)
.hasMessageContaining("Transfer");
}

@Test
void explicitMemoDoesNotRequireChallengeBinding() {
void explicitMemoDoesNotBypassChallengeBinding() {
String merchantMemo = "0x" + "ab".repeat(32);
Map<String, Object> request = new HashMap<>(REQUEST);
request.put("memo", merchantMemo);

Receipt result = intent(new StubRpc(null,
assertThatThrownBy(() -> intent(new StubRpc(null,
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, merchantMemo), 0))
.verify(hashCredential("0xpushedtx"), request);
assertThat(result.status()).isEqualTo("success");
.verify(hashCredential("0xpushedtx"), request))
.isInstanceOf(VerificationFailedException.class)
.hasMessageContaining("memo is not bound to this challenge");
}

@Test
void explicitMemoInMethodDetailsIsHonored() {
void explicitMemoInMethodDetailsStillRequiresChallengeBinding() {
String merchantMemo = "0x" + "ab".repeat(32);
Map<String, Object> request = Map.of(
"amount", String.valueOf(AMOUNT_ATOMIC),
Expand All @@ -416,10 +419,60 @@ void explicitMemoInMethodDetailsIsHonored() {
"methodDetails", Map.of("chainId", CHAIN_ID, "memo", merchantMemo)
);

Receipt result = intent(new StubRpc(null,
assertThatThrownBy(() -> intent(new StubRpc(null,
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, merchantMemo), 0))
.verify(hashCredential("0xpushedtx"), request);
assertThat(result.status()).isEqualTo("success");
.verify(hashCredential("0xpushedtx"), request))
.isInstanceOf(VerificationFailedException.class)
.hasMessageContaining("memo is not bound to this challenge");
}

@Test
void sharedExplicitMemoCannotSatisfyADifferentChallenge() {
ChallengeEcho echoA = new ChallengeEcho(
"chal-a", "api.example.com", "tempo", "charge", "e30", "2099-01-01T00:00:00Z", null, null
);
ChallengeEcho echoB = new ChallengeEcho(
"chal-b", "api.example.com", "tempo", "charge", "e30", "2099-01-01T00:00:00Z", null, null
);
String merchantMemo = "0x" + "ab".repeat(32);
Map<String, Object> request = new HashMap<>(REQUEST);
request.put("memo", merchantMemo);
Map<String, Object> paidForB = receiptWithMemoLog(
TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, merchantMemo);

Store store = new MemoryStore();
assertThatThrownBy(() -> intent(new StubRpc(null, paidForB, 0), store)
.verify(hashCredential("0xvictimtx", echoA), request))
.isInstanceOf(VerificationFailedException.class)
.hasMessageContaining("memo is not bound to this challenge");

assertThatThrownBy(() -> intent(new StubRpc(null, paidForB, 0), store)
.verify(hashCredential("0xvictimtx", echoB), request))
.isInstanceOf(VerificationFailedException.class)
.hasMessageContaining("memo is not bound to this challenge");
}

@Test
void stolenBoundPaymentCannotSatisfyADifferentChallenge() {
ChallengeEcho echoA = new ChallengeEcho(
"chal-a", "api.example.com", "tempo", "charge", "e30", "2099-01-01T00:00:00Z", null, null
);
ChallengeEcho echoB = new ChallengeEcho(
"chal-b", "api.example.com", "tempo", "charge", "e30", "2099-01-01T00:00:00Z", null, null
);
String memoForB = Attribution.encode(echoB.realm(), echoB.id());
Store store = new MemoryStore();

assertThatThrownBy(() -> intent(new StubRpc(null,
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, memoForB), 0), store)
.verify(hashCredential("0xvictimtx", echoA), REQUEST))
.isInstanceOf(VerificationFailedException.class)
.hasMessageContaining("memo is not bound to this challenge");

Receipt result = intent(new StubRpc(null,
receiptWithMemoLog(TOKEN_CONTRACT, SENDER, RECIPIENT, AMOUNT_ATOMIC, memoForB), 0), store)
.verify(hashCredential("0xvictimtx", echoB), REQUEST);
assertThat(result.reference()).isEqualTo("0xvictimtx");
}

@Test
Expand Down
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