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test(marmot): welcome tree_hash + confirmation_tag + negative processCommit coverage

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Quartz:
- processWelcome now enforces hash(ratchet_tree) == GroupContext.tree_hash
  and verifies the joiner-derived confirmation_tag matches GroupInfo's,
  closing the gap where a tampered but-signed GroupInfo could diverge
  the joiner's epoch secrets.
- externalJoin does the equivalent tree_hash check.
- Promoted constantTimeEquals to a file-level helper so the companion
  object (processWelcome) can use it alongside instance methods.

Tests:
- New MlsGroupNegativeTest exercises every authenticity knob on inbound
  commits: tampered confirmation_tag, bit-flipped signature, spoofed
  senderLeafIndex, wrong wire_format, empty confirmation_tag, and
  tampered/missing membership_tag — each must throw and leave the
  receiving group's epoch unchanged (atomic-rollback regression cover).
- Fixed stale jvmAndroidTest references to the removed `selfRemove()`
  helper — use `buildSelfRemoveProposalMessage()` (now Pair-returning).

Interop harness:
- Adds tests 14–16 as inverted-role scaffolding (wn drives, amy receives).
  Currently recorded as SKIP with explicit notes:
    14 / 15 block on filtered-direct-path UpdatePath support in
    quartz's applyUpdatePath (RFC 9420 §7.7 path compression).
    16 blocks on a createdAt-sorted KeyPackage fetch path — the current
    fetchFirst-based fetcher is non-deterministic on relay order.
  Preserves the test functions so they start running the moment those
  gaps are closed.
This commit is contained in:
Claude
2026-04-22 13:32:43 +00:00
parent 0c9709455d
commit 816d253a65
6 changed files with 394 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files
quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/marmot/mls/group/MlsGroup.kt
+42 -16
View File
@@ -97,6 +97,18 @@ import com.vitorpamplona.quartz.utils.mac.MacInstance
* val key = group.exporterSecret("marmot", "group-event", 32)
* ```
*/
private fun constantTimeEquals(
a: ByteArray,
b: ByteArray,
): Boolean {
if (a.size != b.size) return false
var result = 0
for (i in a.indices) {
result = result or (a[i].toInt() xor b[i].toInt())
}
return result == 0
}
class MlsGroup private constructor(
private var groupContext: GroupContext,
private val tree: RatchetTree,
@@ -1731,22 +1743,6 @@ class MlsGroup private constructor(
return writer.toByteArray()
}
/**
* Constant-time byte array comparison to prevent timing side-channels.
* Returns true only if both arrays have the same length and contents.
*/
private fun constantTimeEquals(
a: ByteArray,
b: ByteArray,
): Boolean {
if (a.size != b.size) return false
var result = 0
for (i in a.indices) {
result = result or (a[i].toInt() xor b[i].toInt())
}
return result == 0
}
/**
* Apply an Add proposal and return the assigned leaf index.
*/
@@ -2429,6 +2425,15 @@ class MlsGroup private constructor(
"Invalid GroupInfo signature"
}
// RFC 9420 §12.4.3.1: the ratchet_tree extension the joiner
// reconstructs MUST hash to the tree_hash committed in the
// signed GroupContext. Otherwise a compromised signer could
// feed the joiner a tree different from the one encoded in
// the signed context, silently diverging their key schedule.
require(tree.treeHash().contentEquals(groupContext.treeHash)) {
"GroupInfo tree_hash does not match ratchet_tree extension"
}
// Derive epoch secrets directly from memberSecret (RFC 9420 Section 8.3)
// For Welcome, epoch_secret = ExpandWithLabel(member_secret, "epoch", GroupContext, Nh)
val epochSecret =
@@ -2467,6 +2472,19 @@ class MlsGroup private constructor(
val confirmMac = MacInstance("HmacSHA256", epochSecrets.confirmationKey)
confirmMac.update(groupContext.confirmedTranscriptHash)
val confirmationTag = confirmMac.doFinal()
// RFC 9420 §12.4.3.1: the confirmation_tag the joiner would
// derive from the joiner_secret-sourced confirmation_key MUST
// match the confirmation_tag embedded in the signed GroupInfo.
// Without this check a tampered GroupInfo could supply a
// mismatched confirmed_transcript_hash that still passes the
// signature-over-(context, extensions, tag, signer) as long
// as the attacker controls the signer — the confirmation_tag
// binds the epoch secrets to the transcript.
require(constantTimeEquals(groupInfo.confirmationTag, confirmationTag)) {
"GroupInfo confirmation_tag does not match joiner-derived confirmation_key"
}
val interimInput = TlsWriter()
interimInput.putBytes(groupContext.confirmedTranscriptHash)
interimInput.putOpaqueVarInt(confirmationTag)
@@ -2520,6 +2538,14 @@ class MlsGroup private constructor(
"Invalid GroupInfo signature in externalJoin"
}
// RFC 9420 §12.4.3.1: enforce that the reconstructed
// ratchet_tree hashes to the signed tree_hash. Without this,
// a malicious signer could serve an externalJoin consumer
// a tree that diverges from the signed context.
require(tree.treeHash().contentEquals(groupContext.treeHash)) {
"externalJoin tree_hash does not match ratchet_tree extension"
}
// Extract external_pub from extensions
val externalPubExt =
groupInfo.extensions.find { it.extensionType == EXTERNAL_PUB_EXTENSION_TYPE }
quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/marmot/mls/group/MlsGroupNegativeTest.kt
+291
View File
@@ -0,0 +1,291 @@
/*
* Copyright (c) 2025 Vitor Pamplona
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
* Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
* AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package com.vitorpamplona.quartz.marmot.mls.group
import com.vitorpamplona.quartz.marmot.mls.codec.TlsReader
import com.vitorpamplona.quartz.marmot.mls.framing.MlsMessage
import com.vitorpamplona.quartz.marmot.mls.framing.PublicMessage
import com.vitorpamplona.quartz.marmot.mls.framing.WireFormat
import kotlin.test.Test
import kotlin.test.assertEquals
import kotlin.test.assertFailsWith
import kotlin.test.assertFalse
import kotlin.test.assertNotEquals
import kotlin.test.assertTrue
/**
* Negative tests: every post-RFC-9420-§6 authenticity check that
* [MlsGroup.processCommit] performs should reject the tampered input AND
* leave the group in its pre-commit state (atomic rollback — no partial
* epoch advance, no mutated tree, no dangling pending proposals).
*/
class MlsGroupNegativeTest {
private data class TwoMemberFixture(
val alice: MlsGroup,
val bob: MlsGroup,
val charliePkg: ByteArray,
)
/**
* Produce a 2-member group (alice creator, bob joined via Welcome)
* plus a spare KeyPackage for Charlie. Callers use Charlie's bundle to
* drive Alice into producing a fresh Add commit that Bob will process.
*/
private fun twoMemberGroup(): TwoMemberFixture {
val alice = MlsGroup.create(identity = "alice".encodeToByteArray())
val bobBundle = alice.createKeyPackage(identity = "bob".encodeToByteArray(), signingKey = ByteArray(32) { 1 })
val addBob = alice.addMember(bobBundle.keyPackage.toTlsBytes())
val bob = MlsGroup.processWelcome(addBob.welcomeBytes!!, bobBundle)
val charlieBundle =
alice.createKeyPackage(identity = "charlie".encodeToByteArray(), signingKey = ByteArray(32) { 2 })
return TwoMemberFixture(alice, bob, charlieBundle.keyPackage.toTlsBytes())
}
/**
* Decode a framedCommitBytes (MlsMessage(PublicMessage(commit))) into
* the fields [MlsGroup.processCommit] consumes. Tests re-use this to
* mutate individual fields before re-invoking.
*/
private data class CommitParts(
val content: ByteArray,
val senderLeafIndex: Int,
val confirmationTag: ByteArray,
val signature: ByteArray,
val pubMsg: PublicMessage,
)
private fun parseCommit(framedBytes: ByteArray): CommitParts {
val mlsMsg = MlsMessage.decodeTls(TlsReader(framedBytes))
val pub = PublicMessage.decodeTls(TlsReader(mlsMsg.payload))
return CommitParts(
content = pub.content,
senderLeafIndex = pub.sender.leafIndex,
confirmationTag = pub.confirmationTag!!,
signature = pub.signature,
pubMsg = pub,
)
}
/** Baseline: an honest commit applies and advances Bob's epoch. */
@Test
fun honestCommitIsAccepted() {
val fx = twoMemberGroup()
val bobEpochBefore = fx.bob.epoch
val commit = fx.alice.addMember(fx.charliePkg)
val parts = parseCommit(commit.framedCommitBytes)
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = parts.senderLeafIndex,
confirmationTag = parts.confirmationTag,
signature = parts.signature,
wireFormat = WireFormat.PUBLIC_MESSAGE,
)
assertEquals(bobEpochBefore + 1, fx.bob.epoch)
}
/**
* Tampered confirmation_tag — flipping a single bit must fail the
* HMAC compare, throw, and leave Bob on the original epoch.
*/
@Test
fun tamperedConfirmationTagIsRejectedAndStateRolledBack() {
val fx = twoMemberGroup()
val epochBefore = fx.bob.epoch
val commit = fx.alice.addMember(fx.charliePkg)
val parts = parseCommit(commit.framedCommitBytes)
val tamperedTag = parts.confirmationTag.copyOf().apply { this[0] = (this[0].toInt() xor 0x01).toByte() }
assertFailsWith<IllegalArgumentException> {
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = parts.senderLeafIndex,
confirmationTag = tamperedTag,
signature = parts.signature,
wireFormat = WireFormat.PUBLIC_MESSAGE,
)
}
assertEquals(epochBefore, fx.bob.epoch)
// And the honest commit still applies cleanly afterwards — proving
// no mutable state leaked across the failed attempt.
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = parts.senderLeafIndex,
confirmationTag = parts.confirmationTag,
signature = parts.signature,
wireFormat = WireFormat.PUBLIC_MESSAGE,
)
assertEquals(epochBefore + 1, fx.bob.epoch)
}
/**
* Tampered FramedContentTBS signature — receiver reconstructs the
* exact same TBS bytes the sender signed; any bit-flip in the
* signature fails Ed25519 verification.
*/
@Test
fun tamperedSignatureIsRejectedAndStateRolledBack() {
val fx = twoMemberGroup()
val epochBefore = fx.bob.epoch
val commit = fx.alice.addMember(fx.charliePkg)
val parts = parseCommit(commit.framedCommitBytes)
val tamperedSig = parts.signature.copyOf().apply { this[0] = (this[0].toInt() xor 0x80).toByte() }
assertFailsWith<IllegalArgumentException> {
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = parts.senderLeafIndex,
confirmationTag = parts.confirmationTag,
signature = tamperedSig,
wireFormat = WireFormat.PUBLIC_MESSAGE,
)
}
assertEquals(epochBefore, fx.bob.epoch)
}
/**
* Claiming the commit came from the wrong leaf index — the signature
* was bound to the original sender leaf, so verifying against a
* different leaf's pre-commit signatureKey fails.
*/
@Test
fun spoofedSenderLeafIndexIsRejected() {
val fx = twoMemberGroup()
val epochBefore = fx.bob.epoch
val commit = fx.alice.addMember(fx.charliePkg)
val parts = parseCommit(commit.framedCommitBytes)
// Alice is leaf 0, Bob is leaf 1. Swap.
val wrongLeaf = if (parts.senderLeafIndex == 0) 1 else 0
assertFailsWith<IllegalArgumentException> {
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = wrongLeaf,
confirmationTag = parts.confirmationTag,
signature = parts.signature,
wireFormat = WireFormat.PUBLIC_MESSAGE,
)
}
assertEquals(epochBefore, fx.bob.epoch)
}
/**
* Declaring the wrong wire_format at the receiver — the FramedContentTBS
* hash diverges and signature verification fails, because the sender
* mixed wire_format=PUBLIC_MESSAGE into their TBS bytes.
*/
@Test
fun wrongWireFormatIsRejected() {
val fx = twoMemberGroup()
val epochBefore = fx.bob.epoch
val commit = fx.alice.addMember(fx.charliePkg)
val parts = parseCommit(commit.framedCommitBytes)
assertFailsWith<IllegalArgumentException> {
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = parts.senderLeafIndex,
confirmationTag = parts.confirmationTag,
signature = parts.signature,
wireFormat = WireFormat.PRIVATE_MESSAGE,
)
}
assertEquals(epochBefore, fx.bob.epoch)
}
/**
* Empty confirmation_tag is rejected explicitly — RFC 9420 §6 requires
* every commit to carry a confirmation_tag, and an omitted tag means
* the receiver has no authentication of the post-commit epoch secrets.
*/
@Test
fun emptyConfirmationTagIsRejected() {
val fx = twoMemberGroup()
val epochBefore = fx.bob.epoch
val commit = fx.alice.addMember(fx.charliePkg)
val parts = parseCommit(commit.framedCommitBytes)
assertFailsWith<IllegalArgumentException> {
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = parts.senderLeafIndex,
confirmationTag = ByteArray(0),
signature = parts.signature,
wireFormat = WireFormat.PUBLIC_MESSAGE,
)
}
assertEquals(epochBefore, fx.bob.epoch)
}
/**
* Tampered membership_tag — PublicMessage commits from a member must
* carry an HMAC(membership_key, TBM) that matches what the receiver
* can reconstruct from the current epoch's membership_key. Without
* this check, an outsider that learned the outer exporter secret
* could forge arbitrary commit bodies.
*
* This is enforced at the MarmotInboundProcessor layer before
* [MlsGroup.processCommit] is called; the group exposes
* [MlsGroup.verifyPublicMessageCommitMembershipTag] so the processor
* can short-circuit on tag mismatch.
*/
@Test
fun tamperedMembershipTagFailsPublicMessageCheck() {
val fx = twoMemberGroup()
val commit = fx.alice.addMember(fx.charliePkg)
val parts = parseCommit(commit.framedCommitBytes)
// Honest tag is valid.
assertTrue(fx.bob.verifyPublicMessageCommitMembershipTag(parts.pubMsg))
// Flip one bit in the wire tag — must be rejected.
val original = parts.pubMsg.membershipTag!!
val tampered = original.copyOf().apply { this[0] = (this[0].toInt() xor 0x01).toByte() }
val badPub = parts.pubMsg.copy(membershipTag = tampered)
assertFalse(fx.bob.verifyPublicMessageCommitMembershipTag(badPub))
// A missing tag is also rejected.
val missingPub = parts.pubMsg.copy(membershipTag = null)
assertFalse(fx.bob.verifyPublicMessageCommitMembershipTag(missingPub))
// And the honest commit still applies — nothing got mutated by the checks.
val epochBefore = fx.bob.epoch
fx.bob.processCommit(
commitBytes = parts.content,
senderLeafIndex = parts.senderLeafIndex,
confirmationTag = parts.confirmationTag,
signature = parts.signature,
wireFormat = WireFormat.PUBLIC_MESSAGE,
)
assertEquals(epochBefore + 1, fx.bob.epoch)
assertNotEquals(epochBefore, fx.bob.epoch)
}
}
quartz/src/jvmAndroidTest/kotlin/com/vitorpamplona/quartz/marmot/MarmotMipBehaviorTest.kt
+3 -3
View File
@@ -173,7 +173,7 @@ class MarmotMipBehaviorTest {
val alice = manager.getGroup(groupId)!!
assertFailsWith<IllegalStateException> { alice.proposeSelfRemove() }
assertFailsWith<IllegalStateException> { alice.selfRemove() }
assertFailsWith<IllegalStateException> { alice.buildSelfRemoveProposalMessage() }
}
@Test
@@ -187,8 +187,8 @@ class MarmotMipBehaviorTest {
manager.updateGroupExtensions(groupId, listOf(strangerAdmin.toExtension()))
val alice = manager.getGroup(groupId)!!
// selfRemove (standalone proposal helper) should succeed for a non-admin.
val bytes = alice.selfRemove()
// Standalone SelfRemove proposal helper should succeed for a non-admin.
val (bytes, _) = alice.buildSelfRemoveProposalMessage()
assertTrue(bytes.isNotEmpty())
}
quartz/src/jvmAndroidTest/kotlin/com/vitorpamplona/quartz/marmot/mls/MlsGroupTest.kt
+1 -1
View File
@@ -272,7 +272,7 @@ class MlsGroupTest {
@Test
fun testSelfRemove() {
val group = MlsGroup.create("alice".encodeToByteArray())
val selfRemoveBytes = group.selfRemove()
val (selfRemoveBytes, _) = group.buildSelfRemoveProposalMessage()
assertTrue(selfRemoveBytes.isNotEmpty())
}
tools/marmot-interop/headless/tests-extras.sh
+54
View File
@@ -178,3 +178,57 @@ test_13_keypackage_rotation() {
record_result "$id" fail "no new KP event_id observed"
fi
}
# -- Inverted-role tests ----------------------------------------------------
# Tests 01–13 mostly exercise amethyst as the committer and wn as the
# receiver. The scenarios below are complementary: wn drives the state
# change and amy is the receiver that must accept, verify and apply it.
# This widens coverage for the post-fix inbound authenticity checks
# (membership_tag, FramedContentTBS signature, LeafNode lifetime,
# confirmation_tag) that now run on every commit amy processes.
test_14_wn_removes_a() {
banner "Test 14 — wn (admin) removes A; amy processes Remove"
local id="14 wn removes amy"
# Known gap: wn (mdk-core/openmls) emits the filtered direct-path
# form of UpdatePath on Remove commits per RFC 9420 §7.7 — when the
# copath of a direct-path node has an empty resolution (every leaf
# under it is blank) the corresponding UpdatePathNode is omitted.
# Quartz's RatchetTree.applyUpdatePath currently requires the
# unfiltered node count (`pathNodes.size == directPath.size`) so
# every wn->amy Remove triggers
# "UpdatePath node count (N) doesn't match direct path length (N+k)".
# That's a pre-existing quartz conformance bug, out of scope for
# this branch; the harness carries the test so it starts passing
# the moment the filtered-path path is wired up.
record_result "$id" skip "pending filtered_direct_path support in applyUpdatePath"
}
test_15_wn_member_leaves() {
banner "Test 15 — wn_c leaves; amy + wn_b process SelfRemove"
local id="15 wn_c leaves"
# Same filtered_direct_path gap as test 14: when wn_c leaves a
# 3-member group, wn_b folds the SelfRemove into a commit whose
# UpdatePath uses RFC 9420 §7.7 filtering, and amy's strict
# applyUpdatePath rejects it. Skip until quartz handles the
# filtered form on inbound.
record_result "$id" skip "pending filtered_direct_path support in applyUpdatePath"
}
test_16_wn_keypackage_rotation() {
banner "Test 16 — wn rotates KeyPackage; amy discovers new KP"
local id="16 wn keypackage rotation"
# amy's KeyPackageFetcher.fetchKeyPackage calls client.fetchFirst,
# which returns the first matching event a relay sends — nostr-rs-relay
# typically serves kind:443 events in storage order, not created_at
# order, so after a rotation amy may keep seeing the older event_id
# depending on which arrives first. Making this test deterministic
# requires a "fetch latest by created_at" KeyPackage fetcher; until
# then the check flaps. The inverse direction (test 13, amy rotates
# and wn sees via `wn keys check` which is an addressable index) is
# the reliable one.
record_result "$id" skip "pending createdAt-sorted KeyPackage fetch path"
}
tools/marmot-interop/marmot-interop-headless.sh
+3
View File
@@ -105,3 +105,6 @@ test_10_concurrent_commits
test_11_leave_group
test_12_offline_catchup
test_13_keypackage_rotation
test_14_wn_removes_a
test_15_wn_member_leaves
test_16_wn_keypackage_rotation