From 69ce927b6d509bdffcb6c84d60509736168c6600 Mon Sep 17 00:00:00 2001
From: tajniak81 <13187254+tajniak81@users.noreply.github.com>
Date: Sun, 18 Oct 2026 16:56:28 +0200
Subject: [PATCH] Web client: E2EE on by default, trust shields, identity
 verification, QR

- New rooms (public too) and direct messages are end-to-end encrypted by
  default.
- Per-message trust: "Not verified" for sessions you haven't verified,
  and what is wrong for unsigned sessions, mismatched keys or plain text
  in an encrypted room (src/matrix/trust.ts).
- Verify a person's identity in a room you share (your DM first), and
  QR-code verification both ways: show ours, scan theirs with the camera
  (qrcode-generator, jsqr).
- Warnings when someone's identity changes, with acknowledge, verify
  again or withdraw verification.
- Encrypted thumbnails for large images.
- A tab-only session encrypts its crypto store with a key kept in
  sessionStorage; stores unused for two weeks are deleted.
- Reset encryption fixed: new secret storage first, so the new
  cross-signing keys survive a stale /keys/query answer; status checks
  no longer query our own keys mid-setup.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 apps/web/README.md                            |  56 +++---
 apps/web/package.json                         |   2 +
 apps/web/src/components/CreateRoomDialog.vue  |   9 +-
 apps/web/src/components/QrCode.vue            |  30 ++++
 apps/web/src/components/QrScanner.vue         |  73 ++++++++
 apps/web/src/components/RoomTimeline.vue      |  17 +-
 apps/web/src/components/SessionsDialog.vue    |  35 +++-
 .../web/src/components/VerificationDialog.vue | 143 +++++++++++++--
 apps/web/src/main.ts                          |   3 +-
 apps/web/src/matrix/client.ts                 | 106 ++++++++++-
 apps/web/src/matrix/crypto.ts                 | 164 ++++++++++++++----
 apps/web/src/matrix/send.ts                   |  55 +++++-
 apps/web/src/matrix/timeline.ts               |  14 ++
 apps/web/src/matrix/trust.ts                  | 108 ++++++++++++
 apps/web/src/stores/chat.ts                   |  27 ++-
 apps/web/src/stores/security.ts               |  20 ++-
 apps/web/src/stores/session.ts                |  21 ++-
 apps/web/src/views/RoomView.vue               |  58 +++++++
 pnpm-lock.yaml                                |  16 ++
 19 files changed, 845 insertions(+), 112 deletions(-)
 create mode 100644 apps/web/src/components/QrCode.vue
 create mode 100644 apps/web/src/components/QrScanner.vue
 create mode 100644 apps/web/src/matrix/trust.ts

diff --git a/apps/web/README.md b/apps/web/README.md
index d5ef2e9..1d46536 100644
--- a/apps/web/README.md
+++ b/apps/web/README.md
@@ -48,44 +48,44 @@ that one origin.
 - Read receipts, typing notifications, deleting messages.
 - End-to-end encryption, with the Rust crypto stack matrix-js-sdk loads
   (`matrix-sdk-crypto-wasm`): reading and sending in encrypted rooms,
-  files included (encrypted in the browser before they are uploaded).
-  A message this session can't decrypt says why, such as "sent before
-  this session signed in", not just "encrypted".
-- Verification: verify someone's session from the room's member list,
-  or this session from one of your others, by comparing emoji (SAS).
-  Requests from others open a dialog to accept or decline.
+  files included (encrypted in the browser before they are uploaded, with
+  an encrypted thumbnail for large images). A message this session can't
+  decrypt says why, such as "sent before this session signed in", not
+  just "encrypted".
+- Trust on every message: one from a session you haven't verified says
+  *Not verified*; one with something wrong (an unsigned session,
+  mismatched keys, plain text in an encrypted room) says what.
+- Verification: verify a person once (in a room you share, your direct
+  message first) and every session they verify is trusted; or one session
+  at a time; or this session from one of your others. Either side scans
+  the other's QR code (the camera, in the browser) or both compare emoji.
+- Warnings when someone's identity changes: a reset since you first saw
+  them asks you to acknowledge it; a reset since you *verified* them says
+  their sessions are no longer trusted, with Verify again or Withdraw
+  verification.
 - Encryption setup in Settings: cross-signing keys, secret storage and a
   key backup in one step, behind a recovery key shown once. A new session
   verifies itself with the recovery key (or another session) and restores
   older messages from the backup. Reset encryption when the key is lost.
-- New private rooms and direct messages are end-to-end encrypted by
-  default (a direct message only when the other person has a session with
-  keys); Create room has the switch.
-- Create a room (private, or public with an address), start a direct chat,
-  join by address or from the room directory, accept or decline invites,
-  leave.
-- Room info: topic, members and their roles, invite, edit name and topic.
+- New rooms (public ones too) and direct messages are end-to-end
+  encrypted by default; Create room has the switch for turning it off.
 - Settings: display name, avatar, theme, encryption.
 - Phone layout: one pane at a time, the room list is the home screen.
 
-**Not yet:** per-message trust shields (a message from an unverified
-session looks like any other), verifying a person's identity in a direct
-message rather than one session at a time, QR-code verification, a warning
-when someone's identity changes, encrypted thumbnails for images you send
-(the receiving side shows the whole image), and a passphrase for the
-crypto store. After that: replies, reactions, threads, spaces,
-notifications.
+**Not yet:** replies, reactions, threads, spaces, notifications.
 
 ### Encryption keys in the browser
 
 Each session keeps its keys in IndexedDB under its own name
-(`warp-web-crypto:<user>:<session>`), unencrypted at rest like any web
-client's without a passphrase. Signing out deletes them; a session that
-ends some other way (signed out elsewhere, the token revoked) has them
-deleted when the page next starts. A session kept only for the tab
-("Stay signed in" off) leaves its store behind when the tab closes;
-the session can't be reused, but the keys stay until site data is
-cleared. The `.wasm` file is most of the download (about 2 MB
+(`warp-web-crypto:<user>:<session>`). Signing out deletes them; a session
+that ends some other way (signed out elsewhere, the token revoked) has
+them deleted when the page next starts. A session kept only for the tab
+("Stay signed in" off) encrypts its store with a random key that lives
+with its credentials in `sessionStorage`: when the tab closes the key goes
+with it, and the store left behind can't be read; it is deleted after two
+weeks unused. A "Stay signed in" session's store is not encrypted at rest,
+like any web client's without a passphrase.
+The `.wasm` file is most of the download (about 2 MB
 compressed) and needs `script-src 'wasm-unsafe-eval'`, which warp-web's
 Content-Security-Policy allows; it allows no JavaScript `eval`.
 
@@ -132,6 +132,8 @@ empty URL meaning "this origin".
   Content-Security-Policy, `X-Frame-Options: DENY` and
   `Referrer-Policy: no-referrer` with the client's pages.
 - Keep the proxy's read timeout above 30 seconds: `/sync` long-polls.
+- Serve it over HTTPS: browsers only give the page a camera (for scanning
+  QR codes when verifying) and WebCrypto on a secure origin.
 - Allow request bodies as large as the homeserver's
   `media.max_upload_bytes`; uploads pass through warp-web.
 - warp-web adds `X-Forwarded-For`. The homeserver uses it for rate limits
diff --git a/apps/web/package.json b/apps/web/package.json
index 551d707..7e79c38 100644
--- a/apps/web/package.json
+++ b/apps/web/package.json
@@ -12,8 +12,10 @@
   },
   "dependencies": {
     "@warp/ui": "workspace:*",
+    "jsqr": "1.4.0",
     "matrix-js-sdk": "^44.0.0",
     "pinia": "^3.0.3",
+    "qrcode-generator": "1.4.4",
     "vue": "^3.5.22",
     "vue-router": "^4.5.1"
   },
diff --git a/apps/web/src/components/CreateRoomDialog.vue b/apps/web/src/components/CreateRoomDialog.vue
index f16331a..74a8a66 100644
--- a/apps/web/src/components/CreateRoomDialog.vue
+++ b/apps/web/src/components/CreateRoomDialog.vue
@@ -26,9 +26,8 @@ watch(open, (v) => {
   error.value = ''
 })
 
-// End-to-end encrypted by default for a private room. A public one is
-// readable by whoever joins anyway, and history is lost to newcomers.
-watch(isPublic, (v) => (encrypted.value = !v && chat.canEncrypt))
+// End-to-end encrypted by default, public rooms too; turning it off is a
+// choice made here, once: it can't be turned off later.
 
 // A public room's address, from its name: "Homelab ops" → homelab-ops.
 watch(name, (n, old) => {
@@ -97,6 +96,10 @@ async function submit() {
           </p>
           <p class="small m-0 text-ink-muted">
             <template v-if="!chat.canEncrypt">End-to-end encryption didn’t start in this browser.</template>
+            <template v-else-if="encrypted && isPublic">
+              Only the people in the room can read its messages, not the homeserver. People who join later can’t read what was sent
+              before they joined. It can’t be turned off later.
+            </template>
             <template v-else-if="encrypted">Only the people in the room can read its messages, not the homeserver. It can’t be turned off later.</template>
             <template v-else>The homeserver can read this room’s messages.</template>
           </p>
diff --git a/apps/web/src/components/QrCode.vue b/apps/web/src/components/QrCode.vue
new file mode 100644
index 0000000..328027e
--- /dev/null
+++ b/apps/web/src/components/QrCode.vue
@@ -0,0 +1,30 @@
+<script setup lang="ts">
+import qrcode from 'qrcode-generator'
+import { computed } from 'vue'
+
+// A QR code of raw bytes, drawn as one SVG path: dark modules on white,
+// with the quiet zone scanners need, in either theme.
+
+const props = withDefaults(defineProps<{ data: Uint8ClampedArray; size?: number; label: string }>(), { size: 220 })
+
+const code = computed(() => {
+  const qr = qrcode(0, 'L')
+  let s = ''
+  for (const b of props.data) s += String.fromCharCode(b)
+  qr.addData(s, 'Byte')
+  qr.make()
+  const n = qr.getModuleCount()
+  let d = ''
+  for (let r = 0; r < n; r++) {
+    for (let c = 0; c < n; c++) if (qr.isDark(r, c)) d += `M${c + 4} ${r + 4}h1v1h-1z`
+  }
+  return { n: n + 8, d }
+})
+</script>
+
+<template>
+  <svg :width="size" :height="size" :viewBox="`0 0 ${code.n} ${code.n}`" role="img" :aria-label="label" shape-rendering="crispEdges" class="rounded-md">
+    <rect :width="code.n" :height="code.n" fill="#ffffff" />
+    <path :d="code.d" fill="#000000" />
+  </svg>
+</template>
diff --git a/apps/web/src/components/QrScanner.vue b/apps/web/src/components/QrScanner.vue
new file mode 100644
index 0000000..6623925
--- /dev/null
+++ b/apps/web/src/components/QrScanner.vue
@@ -0,0 +1,73 @@
+<script setup lang="ts">
+import jsQR from 'jsqr'
+import { onBeforeUnmount, onMounted, ref } from 'vue'
+import { WBanner, WSpinner } from '@warp/ui'
+
+// The camera, looking for a QR code. Frames are read on a timer, decoded
+// here in the page, and the camera is switched off as soon as a code is
+// found or the scanner goes away.
+
+const emit = defineEmits<{ found: [data: Uint8ClampedArray] }>()
+
+const video = ref<HTMLVideoElement>()
+const error = ref('')
+const starting = ref(true)
+let stream: MediaStream | null = null
+let timer = 0
+const canvas = document.createElement('canvas')
+
+function stop() {
+  window.clearInterval(timer)
+  stream?.getTracks().forEach((t) => t.stop())
+  stream = null
+}
+
+function scan() {
+  const v = video.value
+  if (!v || v.readyState < 2 || !v.videoWidth) return
+  // Scaled down: decoding is the slow part, and codes are large on screen.
+  const scale = Math.min(1, 640 / v.videoWidth)
+  canvas.width = Math.round(v.videoWidth * scale)
+  canvas.height = Math.round(v.videoHeight * scale)
+  const g = canvas.getContext('2d', { willReadFrequently: true })
+  if (!g) return
+  g.drawImage(v, 0, 0, canvas.width, canvas.height)
+  const img = g.getImageData(0, 0, canvas.width, canvas.height)
+  const code = jsQR(img.data, img.width, img.height, { inversionAttempts: 'dontInvert' })
+  if (code?.binaryData.length) {
+    stop()
+    emit('found', Uint8ClampedArray.from(code.binaryData))
+  }
+}
+
+onMounted(async () => {
+  try {
+    if (!navigator.mediaDevices?.getUserMedia) throw new Error('This browser can’t use a camera here.')
+    stream = await navigator.mediaDevices.getUserMedia({ video: { facingMode: 'environment' }, audio: false })
+    if (!video.value) return stop()
+    video.value.srcObject = stream
+    await video.value.play()
+    timer = window.setInterval(scan, 250)
+  } catch (e) {
+    error.value =
+      e instanceof DOMException && e.name === 'NotAllowedError'
+        ? 'Camera access was turned down. Allow it in the browser’s site settings, or compare emoji instead.'
+        : e instanceof Error
+          ? e.message
+          : 'Can’t start the camera.'
+  } finally {
+    starting.value = false
+  }
+})
+onBeforeUnmount(stop)
+</script>
+
+<template>
+  <div class="flex flex-col items-center gap-3">
+    <WBanner v-if="error" tone="warning" class="w-full">{{ error }}</WBanner>
+    <div v-else class="relative aspect-square w-full max-w-[280px] overflow-hidden rounded-md bg-surface-sunken">
+      <video ref="video" class="h-full w-full object-cover" muted playsinline />
+      <span v-if="starting" class="absolute inset-0 flex items-center justify-center"><WSpinner /></span>
+    </div>
+  </div>
+</template>
diff --git a/apps/web/src/components/RoomTimeline.vue b/apps/web/src/components/RoomTimeline.vue
index fd6d303..19c32a3 100644
--- a/apps/web/src/components/RoomTimeline.vue
+++ b/apps/web/src/components/RoomTimeline.vue
@@ -213,9 +213,20 @@ async function confirmDelete() {
               :title="formatDateTime(item.ts)"
             >
               <MessageBody :item="item" @view="(source, name) => (viewing = { source, name })" />
-              <template v-if="item.status === 'failed'" #meta>
-                <button type="button" class="font-semibold text-teal-text hover:underline" @click="retry(item)">Retry</button>
-                <button type="button" class="font-semibold text-ink-muted hover:underline" @click="discard(item)">Delete</button>
+              <template v-if="item.status === 'failed' || item.shield" #meta>
+                <span
+                  v-if="item.shield"
+                  :class="['inline-flex items-center gap-1', item.shield.tone === 'danger' ? 'text-danger' : 'text-warning']"
+                  :title="item.shield.text"
+                >
+                  <WIcon name="shield-alert" :size="14" />
+                  <span>{{ item.shield.tone === 'danger' ? item.shield.text : 'Not verified' }}</span>
+                  <span v-if="item.shield.tone !== 'danger'" class="wp-sr">: {{ item.shield.text }}</span>
+                </span>
+                <template v-if="item.status === 'failed'">
+                  <button type="button" class="font-semibold text-teal-text hover:underline" @click="retry(item)">Retry</button>
+                  <button type="button" class="font-semibold text-ink-muted hover:underline" @click="discard(item)">Delete</button>
+                </template>
               </template>
             </WMessageBubble>
 
diff --git a/apps/web/src/components/SessionsDialog.vue b/apps/web/src/components/SessionsDialog.vue
index 5cd4ef7..37418e7 100644
--- a/apps/web/src/components/SessionsDialog.vue
+++ b/apps/web/src/components/SessionsDialog.vue
@@ -3,7 +3,7 @@ import { computed, ref, watch } from 'vue'
 import { WBadge, WBanner, WButton, WDialog, WIcon, WSpinner } from '@warp/ui'
 import { errorMessage } from '@/lib/format'
 import { client } from '@/matrix/client'
-import { sessionsOf, type SessionInfo } from '@/matrix/crypto'
+import { identityOf, sessionsOf, type IdentityInfo, type SessionInfo } from '@/matrix/crypto'
 import { useSecurity } from '@/stores/security'
 
 // Someone's sessions, as their published keys list them, and whether this
@@ -14,6 +14,8 @@ const props = defineProps<{ userId: string; name: string }>()
 
 const security = useSecurity()
 const sessions = ref<SessionInfo[] | null>(null)
+const identity = ref<IdentityInfo | null>(null)
+const verifyingUser = ref(false)
 const error = ref('')
 const starting = ref('')
 const mine = computed(() => props.userId === client().getUserId())
@@ -21,7 +23,9 @@ const mine = computed(() => props.userId === client().getUserId())
 async function load() {
   error.value = ''
   try {
-    sessions.value = await sessionsOf(props.userId)
+    const [s, id] = await Promise.all([sessionsOf(props.userId), mine.value ? null : identityOf(props.userId)])
+    sessions.value = s
+    identity.value = id
   } catch (e) {
     error.value = errorMessage(e)
   }
@@ -38,6 +42,19 @@ watch(
   () => open.value && void load(),
 )
 
+async function verifyUser() {
+  verifyingUser.value = true
+  error.value = ''
+  try {
+    await security.verifyUser(props.userId)
+    open.value = false
+  } catch (e) {
+    error.value = errorMessage(e)
+  } finally {
+    verifyingUser.value = false
+  }
+}
+
 async function verify(s: SessionInfo) {
   starting.value = s.deviceId
   error.value = ''
@@ -59,8 +76,20 @@ async function verify(s: SessionInfo) {
     </p>
     <p v-else class="small m-0 text-ink-muted">
       Each place <span class="mxid">{{ userId }}</span> is signed in has its own keys. Verify a session to be sure messages from it are
-      really theirs: you’ll both compare seven emoji, so do it together, in person or on a call.
+      really theirs: one of you scans the other’s QR code, or you both compare seven emoji, so do it together, in person or on a call.
     </p>
+    <!-- The person, all their sessions at once -->
+    <div v-if="identity?.hasIdentity" class="flex items-center gap-3 rounded-md bg-surface-sunken px-3 py-3">
+      <WIcon :name="identity.verified ? 'shield-check' : 'shield-alert'" :class="identity.verified ? 'text-teal-text' : 'text-ink-muted'" />
+      <div class="min-w-0 flex-1">
+        <p class="body-strong m-0">{{ identity.verified ? `You verified ${name}` : `You haven’t verified ${name}` }}</p>
+        <p class="small m-0 text-ink-muted">
+          <template v-if="identity.verified">Every session they verify is trusted too.</template>
+          <template v-else>Verify them once, in your direct message, and every session they verify is trusted too.</template>
+        </p>
+      </div>
+      <WButton v-if="!identity.verified" size="sm" variant="primary" :loading="verifyingUser" @click="verifyUser">Verify {{ name }}</WButton>
+    </div>
     <div v-if="!sessions && !error" class="flex justify-center py-4"><WSpinner /></div>
     <p v-else-if="sessions && !sessions.length" class="body m-0 text-ink-muted">
       No sessions with encryption keys. They can’t read end-to-end encrypted messages until they sign in with a client that supports it.
diff --git a/apps/web/src/components/VerificationDialog.vue b/apps/web/src/components/VerificationDialog.vue
index 8387038..a8ea575 100644
--- a/apps/web/src/components/VerificationDialog.vue
+++ b/apps/web/src/components/VerificationDialog.vue
@@ -2,18 +2,22 @@
 import {
   VerificationPhase,
   VerifierEvent,
+  type ShowQrCodeCallbacks,
   type ShowSasCallbacks,
   type Verifier,
 } from 'matrix-js-sdk/lib/crypto-api'
 import { computed, ref, shallowRef, watch } from 'vue'
 import { WBanner, WButton, WDialog, WIcon, WSpinner } from '@warp/ui'
+import QrCode from '@/components/QrCode.vue'
+import QrScanner from '@/components/QrScanner.vue'
 import { errorMessage } from '@/lib/format'
 import { client } from '@/matrix/client'
 import { useSecurity } from '@/stores/security'
 
-// One verification, from the request to the emoji to "Verified": either
-// this session asked (Verify session) or someone else did. Both sides see
-// the same seven emoji when nobody is in the middle.
+// One verification, from the request to "Verified": either this session
+// asked (Verify session) or someone else did. Once both are ready, either
+// side scans the other's QR code, or both compare seven emoji, which match
+// when nobody is in the middle.
 
 const security = useSecurity()
 
@@ -33,6 +37,11 @@ const open = computed({
 })
 
 const sas = shallowRef<ShowSasCallbacks | null>(null)
+const reciprocate = shallowRef<ShowQrCodeCallbacks | null>(null)
+const qr = shallowRef<Uint8ClampedArray | null>(null)
+const scanning = ref(false)
+/** We scanned their code: waiting for them to confirm. */
+const scanned = ref(false)
 const confirmed = ref(false)
 const busy = ref(false)
 const error = ref('')
@@ -40,6 +49,10 @@ let verifier: Verifier | null = null
 
 function reset() {
   sas.value = null
+  reciprocate.value = null
+  qr.value = null
+  scanning.value = false
+  scanned.value = false
   confirmed.value = false
   busy.value = false
   error.value = ''
@@ -59,34 +72,80 @@ const otherName = computed(() => {
   return r.otherUserId
 })
 
-// Runs the verifier once there is one: the initiator starts emoji
-// verification as soon as the other side is ready.
+// What the other side can do with QR codes.
+const theyScan = computed(() => {
+  void security.version
+  return Boolean(req.value?.otherPartySupportsMethod('m.qr_code.scan.v1'))
+})
+const theyShow = computed(() => {
+  void security.version
+  return Boolean(req.value?.otherPartySupportsMethod('m.qr_code.show.v1')) && Boolean(navigator.mediaDevices?.getUserMedia)
+})
+
+// Once ready: our QR code for them to scan, if they can. Without QR codes
+// either way, the initiator goes straight to the emoji.
+let qrFor: unknown = null
 watch(
   [req, phase],
   async () => {
     const r = req.value
     if (!r) return
-    if (r.phase === VerificationPhase.Ready && r.initiatedByMe && !r.verifier && !busy.value) {
-      busy.value = true
-      try {
-        await r.startVerification('m.sas.v1')
-      } catch (e) {
-        error.value = errorMessage(e)
-      } finally {
-        busy.value = false
-      }
+    if (r.phase === VerificationPhase.Ready && qrFor !== r) {
+      qrFor = r
+      if (theyScan.value) qr.value = (await r.generateQRCode().catch(() => undefined)) ?? null
+      if (!qr.value && !theyShow.value && r.initiatedByMe && !r.verifier) await startEmoji()
     }
     const v = r.verifier
     if (v && v !== verifier) {
       verifier = v
       v.on(VerifierEvent.ShowSas, (cb) => (sas.value = cb))
+      v.on(VerifierEvent.ShowReciprocateQr, (cb) => (reciprocate.value = cb))
       if (v.getShowSasCallbacks()) sas.value = v.getShowSasCallbacks()
+      if (v.getReciprocateQrCodeCallbacks()) reciprocate.value = v.getReciprocateQrCodeCallbacks()
       v.verify().catch(() => undefined)
     }
   },
   { immediate: true },
 )
 
+async function startEmoji() {
+  const r = req.value
+  if (!r || r.verifier || busy.value) return
+  busy.value = true
+  error.value = ''
+  try {
+    await r.startVerification('m.sas.v1')
+  } catch (e) {
+    error.value = errorMessage(e)
+  } finally {
+    busy.value = false
+  }
+}
+
+async function onScanned(data: Uint8ClampedArray) {
+  scanning.value = false
+  busy.value = true
+  error.value = ''
+  try {
+    // The verifier that comes of it is picked up and run above.
+    await req.value?.scanQRCode(data)
+    scanned.value = true
+  } catch (e) {
+    error.value = `That code didn’t work: ${errorMessage(e)}`
+  } finally {
+    busy.value = false
+  }
+}
+
+function reciprocateYes() {
+  confirmed.value = true
+  reciprocate.value?.confirm()
+}
+
+function reciprocateNo() {
+  reciprocate.value?.cancel()
+}
+
 async function accept() {
   busy.value = true
   error.value = ''
@@ -134,7 +193,12 @@ const cancelText = computed(() => {
   }
 })
 
-const title = computed(() => (req.value?.isSelfVerification ? 'Verify this session' : 'Verify session'))
+const title = computed(() => {
+  const r = req.value
+  if (r?.isSelfVerification) return 'Verify this session'
+  // In a room: the person, all their sessions; to-device: one session.
+  return r?.roomId ? `Verify ${otherName.value}` : 'Verify session'
+})
 </script>
 
 <template>
@@ -159,16 +223,52 @@ const title = computed(() => (req.value?.isSelfVerification ? 'Verify this sessi
           </span>
           <span v-else>
             <span class="body-strong">{{ otherName }}</span><template v-if="otherName !== req.otherUserId">
-              (<span class="mxid">{{ req.otherUserId }}</span>)</template> wants to verify your session.
+              (<span class="mxid">{{ req.otherUserId }}</span>)</template> wants to verify {{ req.roomId ? 'you' : 'your session' }}.
           </span>
         </p>
-        <p class="small m-0 text-ink-muted">You’ll both compare seven emoji. Accept only if you expected this.</p>
+        <p class="small m-0 text-ink-muted">One of you scans the other’s QR code, or you both compare seven emoji. Accept only if you expected this.</p>
       </div>
 
-      <!-- Ready, about to compare -->
+      <!-- We scanned their code -->
+      <div v-else-if="scanned && phase !== VerificationPhase.Done && phase !== VerificationPhase.Cancelled" class="flex flex-col items-center gap-3 py-2 text-center">
+        <WIcon name="shield-check" :size="40" class="text-teal-text" />
+        <p class="body m-0">The code checks out. Waiting for {{ otherName }} to confirm on their side…</p>
+      </div>
+
+      <!-- Ready: pick a way, unless one was picked already -->
+      <div v-else-if="phase === VerificationPhase.Ready && !req.verifier && (qr || theyShow)" class="flex flex-col items-center gap-4 text-center">
+        <template v-if="scanning">
+          <p class="body m-0">Point the camera at the QR code {{ otherName }} shows.</p>
+          <QrScanner @found="onScanned" />
+        </template>
+        <template v-else>
+          <template v-if="qr">
+            <p class="body m-0">Scan this code with {{ req.isSelfVerification ? 'your other session' : `${otherName}’s session` }}.</p>
+            <QrCode :data="qr" label="QR code to verify this session" />
+          </template>
+          <p v-else class="body m-0">Scan the QR code on {{ req.isSelfVerification ? 'your other session' : `${otherName}’s screen` }}, or compare emoji.</p>
+        </template>
+        <div class="flex flex-wrap justify-center gap-2">
+          <WButton v-if="theyShow && !scanning" icon="image" :disabled="busy" @click="scanning = true">Scan their code</WButton>
+          <WButton v-if="scanning" variant="ghost" @click="scanning = false">Stop scanning</WButton>
+          <WButton :loading="busy" @click="startEmoji">Compare emoji instead</WButton>
+        </div>
+      </div>
+
+      <!-- They scanned our code: did it work on their side? -->
+      <div v-else-if="phase === VerificationPhase.Started && reciprocate" class="flex flex-col items-center gap-3 py-2 text-center">
+        <WIcon name="shield-check" :size="40" class="text-teal-text" />
+        <p class="body m-0">
+          {{ req.isSelfVerification ? 'Your other session' : otherName }} scanned the code. Does
+          {{ req.isSelfVerification ? 'it' : 'their screen' }} show a shield with a check mark?
+        </p>
+        <p v-if="confirmed" class="small m-0 flex items-center gap-2 text-ink-muted"><WSpinner :size="14" /> Finishing…</p>
+      </div>
+
+      <!-- Working -->
       <div v-else-if="(phase === VerificationPhase.Ready || phase === VerificationPhase.Started) && !sas" class="flex flex-col items-center gap-4 py-2 text-center">
         <WSpinner :size="28" />
-        <p class="body m-0">Getting the emoji ready…</p>
+        <p class="body m-0">{{ req.chosenMethod === 'm.reciprocate.v1' ? 'Checking the code…' : 'Getting the emoji ready…' }}</p>
       </div>
 
       <!-- Compare the emoji -->
@@ -194,6 +294,7 @@ const title = computed(() => (req.value?.isSelfVerification ? 'Verify this sessi
         <p class="body-strong m-0">Verified</p>
         <p class="body m-0 text-ink-muted">
           <template v-if="req.isSelfVerification">This session is verified. Your other sessions trust it, and it can read your encrypted messages.</template>
+          <template v-else-if="req.roomId">You verified {{ otherName }}. Every session they verify is trusted too.</template>
           <template v-else>
             You verified {{ otherName }}’s session<template v-if="req.otherDeviceId"> <span class="mxid">{{ req.otherDeviceId }}</span></template>.
           </template>
@@ -211,6 +312,10 @@ const title = computed(() => (req.value?.isSelfVerification ? 'Verify this sessi
         <WButton variant="ghost" :disabled="busy" @click="open = false">Decline</WButton>
         <WButton variant="primary" :loading="busy" @click="accept">Accept</WButton>
       </template>
+      <template v-else-if="phase === VerificationPhase.Started && reciprocate && !confirmed">
+        <WButton variant="danger" @click="reciprocateNo">No</WButton>
+        <WButton variant="primary" icon="check" @click="reciprocateYes">Yes, it does</WButton>
+      </template>
       <template v-else-if="phase === VerificationPhase.Started && sas && !confirmed">
         <WButton variant="danger" :disabled="busy" @click="mismatch">They don’t match</WButton>
         <WButton variant="primary" icon="check" :loading="busy" @click="match">They match</WButton>
diff --git a/apps/web/src/main.ts b/apps/web/src/main.ts
index 41517aa..aadf1a2 100644
--- a/apps/web/src/main.ts
+++ b/apps/web/src/main.ts
@@ -3,6 +3,7 @@ import { createApp } from 'vue'
 import App from './App.vue'
 import { loadConfig } from './config'
 import { forgetEndedSessions } from './matrix/client'
+import { savedCryptoStores } from './stores/session'
 import { router } from './router'
 import './style.css'
 
@@ -10,6 +11,6 @@ import './style.css'
 // before anything talks to it.
 loadConfig().then(() => {
   // Encryption keys of sessions that ended while their store was open.
-  void forgetEndedSessions()
+  void forgetEndedSessions(savedCryptoStores())
   createApp(App).use(createPinia()).use(router).mount('#app')
 })
diff --git a/apps/web/src/matrix/client.ts b/apps/web/src/matrix/client.ts
index 940b333..2a6c42e 100644
--- a/apps/web/src/matrix/client.ts
+++ b/apps/web/src/matrix/client.ts
@@ -15,6 +15,22 @@ export interface Credentials {
   userId: string
   deviceId: string
   accessToken: string
+  /**
+   * A session kept only for the tab encrypts its crypto store with this
+   * key (base64, 32 bytes), which lives with the credentials in
+   * sessionStorage: once the tab is gone, so is any way to read the store.
+   */
+  storageKey?: string
+}
+
+/** A new random key for a tab-only session's crypto store. */
+export function newStorageKey(): string {
+  const bytes = crypto.getRandomValues(new Uint8Array(32))
+  return btoa(String.fromCharCode(...bytes))
+}
+
+function decodeKey(b64: string): Uint8Array {
+  return Uint8Array.from(atob(b64), (ch) => ch.charCodeAt(0))
 }
 
 let current: MatrixClient | null = null
@@ -53,8 +69,9 @@ export async function startClient(creds: Credentials): Promise<MatrixClient> {
     timelineSupport: true,
     useAuthorizationHeader: true,
     cryptoCallbacks,
-    // Emoji (SAS) only: there is no camera to scan a QR code with here.
-    verificationMethods: ['m.sas.v1'],
+    // Emoji (SAS), and QR codes both ways: shown here, or scanned with
+    // the camera.
+    verificationMethods: ['m.sas.v1', 'm.qr_code.show.v1', 'm.qr_code.scan.v1', 'm.reciprocate.v1'],
   })
   current = c
   // End-to-end encryption: the Rust crypto stack (matrix-sdk-crypto-wasm),
@@ -62,8 +79,13 @@ export async function startClient(creds: Credentials): Promise<MatrixClient> {
   // in one browser never share a store. It loads before the first sync so
   // the to-device messages and room keys in it are not missed.
   cryptoFailure = ''
+  const prefix = cryptoDatabasePrefix(creds.userId, creds.deviceId)
+  startHeartbeat(prefix)
   try {
-    await c.initRustCrypto({ cryptoDatabasePrefix: cryptoDatabasePrefix(creds.userId, creds.deviceId) })
+    await c.initRustCrypto({
+      cryptoDatabasePrefix: prefix,
+      storageKey: creds.storageKey ? decodeKey(creds.storageKey) : undefined,
+    })
     bindCrypto(c)
   } catch (e) {
     console.error('crypto: ', e)
@@ -81,6 +103,7 @@ export async function startClient(creds: Credentials): Promise<MatrixClient> {
 }
 
 export function stopClient() {
+  stopHeartbeat()
   if (!current) return
   bindCrypto(null)
   current.stopClient()
@@ -142,13 +165,80 @@ export async function destroyClient(session?: { userId: string; deviceId: string
   if (!userId || !deviceId) return
   const prefix = cryptoDatabasePrefix(userId, deviceId)
   setPendingForget([...new Set([...pendingForget(), prefix])])
+  setAlive(prefix, null)
   await deleteStore(c, prefix)
 }
 
-/** Finishes deleting the crypto stores of sessions that ended. Runs before any client starts. */
-export async function forgetEndedSessions() {
-  const list = pendingForget()
-  if (!list.length) return
+// Each running session says it is alive every minute, so a page starting
+// later can tell a store in use (another tab) from one left behind by a tab
+// that closed. A store unused this long is deleted.
+const aliveKey = 'warp.web.crypto.alive'
+const abandonedAfterMs = 14 * 24 * 3600_000
+let heartbeat = 0
+let heartbeatPrefix = ''
+
+function aliveMap(): Record<string, number> {
+  try {
+    const v = JSON.parse(localStorage.getItem(aliveKey) ?? '{}')
+    return v && typeof v === 'object' ? (v as Record<string, number>) : {}
+  } catch {
+    return {}
+  }
+}
+
+function setAlive(prefix: string, ts: number | null) {
+  try {
+    const m = aliveMap()
+    if (ts === null) delete m[prefix]
+    else m[prefix] = ts
+    localStorage.setItem(aliveKey, JSON.stringify(m))
+  } catch {
+    // Without it, a store left behind is only deleted when site data is.
+  }
+}
+
+function startHeartbeat(prefix: string) {
+  stopHeartbeat()
+  heartbeatPrefix = prefix
+  setAlive(prefix, Date.now())
+  heartbeat = window.setInterval(() => setAlive(prefix, Date.now()), 60_000)
+}
+
+function stopHeartbeat() {
+  window.clearInterval(heartbeat)
+  heartbeat = 0
+  heartbeatPrefix = ''
+}
+
+const storeSuffix = '::matrix-sdk-crypto'
+
+/**
+ * Housekeeping before any client starts: finishes deleting the stores of
+ * sessions that ended, and deletes stores a closed tab left behind (a
+ * tab-only session's, unreadable without the tab's key anyway).
+ * `keep` lists the stores of sessions this browser still has credentials for.
+ */
+export async function forgetEndedSessions(keep: string[]) {
   const c = anonymousClient()
-  for (const prefix of list) await deleteStore(c, prefix)
+  for (const prefix of pendingForget()) await deleteStore(c, prefix)
+  let names: string[] = []
+  try {
+    names = (await indexedDB.databases()).map((d) => d.name ?? '')
+  } catch {
+    return
+  }
+  const alive = aliveMap()
+  const now = Date.now()
+  for (const name of names) {
+    if (!name.startsWith('warp-web-crypto:') || !name.endsWith(storeSuffix)) continue
+    const prefix = name.slice(0, -storeSuffix.length)
+    if (keep.includes(prefix) || prefix === heartbeatPrefix) continue
+    // Never seen alive (a store from before this was kept): start its clock now.
+    if (alive[prefix] === undefined) {
+      setAlive(prefix, now)
+      continue
+    }
+    if (now - alive[prefix]! < abandonedAfterMs) continue
+    if (await deleteStore(c, prefix)) setAlive(prefix, null)
+  }
 }
diff --git a/apps/web/src/matrix/crypto.ts b/apps/web/src/matrix/crypto.ts
index e5fc6ff..f6d4010 100644
--- a/apps/web/src/matrix/crypto.ts
+++ b/apps/web/src/matrix/crypto.ts
@@ -73,13 +73,22 @@ export interface EncryptionStatus {
   backupKey: boolean
 }
 
+let settingUp = false
+
+/** Encryption is being set up or reset: status checks wait for it. */
+export function isSettingUp(): boolean {
+  return settingUp
+}
+
 export async function encryptionStatus(): Promise<EncryptionStatus> {
   const api = crypto()
   const c = current!
   const userId = c.getUserId()!
   const deviceId = c.getDeviceId()!
   const [crossSigning, device, secretStorage, backupInfo, backupActive, backupKey] = await Promise.all([
-    api.userHasCrossSigningKeys(userId, true),
+    // The local copy: sync keeps our own keys current, and asking the
+    // homeserver mid-setup races the upload of new ones.
+    api.userHasCrossSigningKeys(userId, false),
     api.getDeviceVerificationStatus(userId, deviceId),
     api.isSecretStorageReady(),
     api.getKeyBackupInfo().catch(() => null),
@@ -117,47 +126,83 @@ function uiaSession(e: unknown): string | undefined | null {
  * verified this account has to verify it again.
  */
 export async function setUpEncryption(opts: { password?: string; reset?: boolean }): Promise<string> {
+  settingUp = true
+  try {
+    return await setUp(opts)
+  } finally {
+    settingUp = false
+  }
+}
+
+async function setUp(opts: { password?: string; reset?: boolean }): Promise<string> {
   const api = crypto()
   const c = current!
-  await api.bootstrapCrossSigning({
-    setupNewCrossSigning: opts.reset ?? false,
-    authUploadDeviceSigningKeys: async (makeRequest) => {
-      try {
-        await makeRequest(null)
-      } catch (e) {
-        const session = uiaSession(e)
-        if (session === null) throw e
-        if (!opts.password) throw new PasswordNeededError()
-        const auth: AuthDict = {
-          type: 'm.login.password',
-          identifier: { type: 'm.id.user', user: c.getUserId()! },
-          password: opts.password,
-          session,
-        }
-        try {
-          await makeRequest(auth)
-        } catch (e2) {
-          if (uiaSession(e2) !== null || (e2 instanceof MatrixError && e2.errcode === 'M_FORBIDDEN')) {
-            throw new Error('That password isn’t right.')
-          }
-          throw e2
-        }
+  const authUploadDeviceSigningKeys = async (makeRequest: (auth: AuthDict | null) => Promise<void>) => {
+    try {
+      await makeRequest(null)
+    } catch (e) {
+      const session = uiaSession(e)
+      if (session === null) throw e
+      if (!opts.password) throw new PasswordNeededError()
+      const auth: AuthDict = {
+        type: 'm.login.password',
+        identifier: { type: 'm.id.user', user: c.getUserId()! },
+        password: opts.password,
+        session,
       }
-    },
-  })
+      try {
+        await makeRequest(auth)
+      } catch (e2) {
+        if (uiaSession(e2) !== null || (e2 instanceof MatrixError && e2.errcode === 'M_FORBIDDEN')) {
+          throw new Error('That password isn’t right.')
+        }
+        throw e2
+      }
+    }
+  }
   let recoveryKey = ''
-  await api.bootstrapSecretStorage({
-    setupNewSecretStorage: true,
-    setupNewKeyBackup: true,
-    createSecretStorageKey: async () => {
-      const key = await api.createRecoveryKeyFromPassphrase()
-      recoveryKey = key.encodedPrivateKey ?? ''
-      return key
-    },
-  })
+  const createSecretStorageKey = async () => {
+    const key = await api.createRecoveryKeyFromPassphrase()
+    recoveryKey = key.encodedPrivateKey ?? ''
+    return key
+  }
+  if (opts.reset) {
+    // New secret storage (and a new key backup) first, under a new key the
+    // page then holds: the new cross-signing keys are saved into it before
+    // they are uploaded, so nothing is lost if an answer about the old
+    // identity arrives in between.
+    await api.bootstrapSecretStorage({ setupNewSecretStorage: true, setupNewKeyBackup: true, createSecretStorageKey })
+    await api.bootstrapCrossSigning({ setupNewCrossSigning: true, authUploadDeviceSigningKeys })
+  } else {
+    await api.bootstrapCrossSigning({ authUploadDeviceSigningKeys })
+    await api.bootstrapSecretStorage({ setupNewSecretStorage: true, setupNewKeyBackup: true, createSecretStorageKey })
+  }
+  await ensureSelfSigned()
   return recoveryKey
 }
 
+/**
+ * Makes sure this session ended up signed by the account's new identity.
+ * A `/keys/query` answer still carrying the old keys can arrive after the
+ * new ones were made, and the crypto stack then drops the new private
+ * keys; they are in the new secret storage, whose key is cached, so they
+ * are read back from there and this session is signed again.
+ */
+async function ensureSelfSigned() {
+  const api = crypto()
+  const c = current!
+  for (let attempt = 0; attempt < 3; attempt++) {
+    const device = await api.getDeviceVerificationStatus(c.getUserId()!, c.getDeviceId()!)
+    if (device?.crossSigningVerified) return
+    const status = await api.getCrossSigningStatus()
+    if (!status.privateKeysInSecretStorage) return
+    // Reads the keys back from secret storage when they are missing here.
+    await api.bootstrapCrossSigning({})
+    await api.crossSignDevice(c.getDeviceId()!).catch(() => undefined)
+    await new Promise((r) => setTimeout(r, 1000))
+  }
+}
+
 async function keyFromInput(input: string, info: SecretStorageKeyDescription): Promise<Uint8Array<ArrayBuffer>> {
   const text = input.trim()
   try {
@@ -252,3 +297,52 @@ export function recoveryKeyKnown(): boolean {
 export async function createKeyBackup(): Promise<void> {
   await crypto().bootstrapSecretStorage({ setupNewKeyBackup: true })
 }
+
+/** Whether you verified the person's identity, and whether they have one to verify. */
+export interface IdentityInfo {
+  /** They have cross-signing keys: their identity can be verified. */
+  hasIdentity: boolean
+  verified: boolean
+}
+
+export async function identityOf(userId: string): Promise<IdentityInfo> {
+  const api = crypto()
+  const [hasIdentity, status] = await Promise.all([api.userHasCrossSigningKeys(userId, true), api.getUserVerificationStatus(userId)])
+  return { hasIdentity, verified: status.isCrossSigningVerified() }
+}
+
+/** Verifies a person (their identity, so all their verified sessions) in a room you share, normally your DM. */
+export function verifyUserInRoom(userId: string, roomId: string): Promise<VerificationRequest> {
+  return crypto().requestVerificationDM(userId, roomId)
+}
+
+export interface IdentityWarning {
+  userId: string
+  /** `reset`: a new identity since you first saw them; `verifiedReset`: since you verified them. */
+  kind: 'reset' | 'verifiedReset'
+}
+
+/** People among `userIds` whose identity changed, and who you haven't acknowledged yet. */
+export async function identityWarnings(userIds: string[]): Promise<IdentityWarning[]> {
+  const api = current?.getCrypto()
+  if (!api) return []
+  const me = current!.getUserId()
+  const out: IdentityWarning[] = []
+  for (const userId of userIds) {
+    if (userId === me) continue
+    const s = await api.getUserVerificationStatus(userId)
+    if (s.wasCrossSigningVerified() && !s.isCrossSigningVerified()) out.push({ userId, kind: 'verifiedReset' })
+    else if (s.needsUserApproval) out.push({ userId, kind: 'reset' })
+  }
+  return out
+}
+
+/** Accepts someone's new identity (after a reset you weren't warned about by them). */
+export function acceptIdentity(userId: string): Promise<void> {
+  return crypto().pinCurrentUserIdentity(userId)
+}
+
+/** Stops requiring that someone you verified stay verified, after they reset their identity. */
+export function withdrawVerification(userId: string): Promise<void> {
+  return crypto().withdrawVerificationRequirement(userId)
+}
diff --git a/apps/web/src/matrix/send.ts b/apps/web/src/matrix/send.ts
index 29be9ab..db9e70c 100644
--- a/apps/web/src/matrix/send.ts
+++ b/apps/web/src/matrix/send.ts
@@ -33,6 +33,40 @@ function imageSize(file: File): Promise<{ w: number; h: number } | undefined> {
   })
 }
 
+// Images larger than this get a thumbnail made here, so the timeline loads
+// that instead of the whole file. In an encrypted room the homeserver can't
+// make one, so this is the only thumbnail there is.
+const thumbMax = { w: 800, h: 600 }
+
+interface Thumbnail {
+  blob: Blob
+  w: number
+  h: number
+}
+
+async function makeThumbnail(file: File, size: { w: number; h: number } | undefined): Promise<Thumbnail | undefined> {
+  if (!size || (size.w <= thumbMax.w && size.h <= thumbMax.h && file.size < 256 * 1024)) return undefined
+  if (file.type === 'image/gif' || file.type === 'image/svg+xml') return undefined
+  try {
+    const bitmap = await createImageBitmap(file)
+    const scale = Math.min(1, thumbMax.w / bitmap.width, thumbMax.h / bitmap.height)
+    const w = Math.max(1, Math.round(bitmap.width * scale))
+    const h = Math.max(1, Math.round(bitmap.height * scale))
+    const canvas = document.createElement('canvas')
+    canvas.width = w
+    canvas.height = h
+    canvas.getContext('2d')?.drawImage(bitmap, 0, 0, w, h)
+    bitmap.close()
+    // PNG keeps transparency; anything else is a photo, and JPEG is smaller.
+    const type = file.type === 'image/png' ? 'image/png' : 'image/jpeg'
+    const blob = await new Promise<Blob | null>((resolve) => canvas.toBlob(resolve, type, 0.82))
+    if (!blob || blob.size >= file.size) return undefined
+    return { blob, w, h }
+  } catch {
+    return undefined
+  }
+}
+
 function msgtypeFor(file: File): MsgType {
   if (file.type.startsWith('image/')) return MsgType.Image
   if (file.type.startsWith('video/')) return MsgType.Video
@@ -54,11 +88,28 @@ export async function sendFile(
 ) {
   const msgtype = msgtypeFor(file)
   const info: Record<string, unknown> = { mimetype: file.type || 'application/octet-stream', size: file.size }
-  if (msgtype === MsgType.Image) Object.assign(info, (await imageSize(file)) ?? {})
+  let thumb: Thumbnail | undefined
+  if (msgtype === MsgType.Image) {
+    const size = await imageSize(file)
+    Object.assign(info, size ?? {})
+    thumb = await makeThumbnail(file, size)
+  }
+  const encrypted = room.hasEncryptionStateEvent()
 
   const progressHandler = (p: { loaded: number; total: number }) => onProgress?.({ name: file.name, loaded: p.loaded, total: p.total })
+  if (thumb) {
+    const thumbInfo = { w: thumb.w, h: thumb.h, mimetype: thumb.blob.type, size: thumb.blob.size }
+    if (encrypted) {
+      const { data, file: keys } = await encryptAttachment(await thumb.blob.arrayBuffer())
+      const up = await c.uploadContent(new Blob([data]), { type: 'application/octet-stream', includeFilename: false })
+      Object.assign(info, { thumbnail_file: { ...keys, url: up.content_uri }, thumbnail_info: thumbInfo })
+    } else {
+      const up = await c.uploadContent(thumb.blob, { type: thumb.blob.type, includeFilename: false })
+      Object.assign(info, { thumbnail_url: up.content_uri, thumbnail_info: thumbInfo })
+    }
+  }
   let source: { url: string } | { file: object }
-  if (room.hasEncryptionStateEvent()) {
+  if (encrypted) {
     const { data, file: keys } = await encryptAttachment(await file.arrayBuffer())
     // The name and type stay inside the encrypted message.
     const upload = await c.uploadContent(new Blob([data]), { type: 'application/octet-stream', includeFilename: false, progressHandler })
diff --git a/apps/web/src/matrix/timeline.ts b/apps/web/src/matrix/timeline.ts
index 3dd6aef..2b74dcf 100644
--- a/apps/web/src/matrix/timeline.ts
+++ b/apps/web/src/matrix/timeline.ts
@@ -13,6 +13,7 @@ import type { MessageStatus } from '@warp/ui'
 import { sameDay } from '@/lib/format'
 import type { EncryptedFile } from './attachments'
 import type { MediaSource } from './media'
+import { shieldOf, type Shield } from './trust'
 
 // Turns a room's live timeline into what the timeline view draws: messages
 // grouped by sender, day separators and one-line notices for state changes.
@@ -53,6 +54,8 @@ export interface MessageItem {
   utd?: string
   /** Sent end-to-end encrypted. */
   e2ee: boolean
+  /** Why this message may not be from who it says, when that's in doubt. */
+  shield?: Shield
   status?: MessageStatus
   /** First of a run of messages from one sender: shows the name. */
   first: boolean
@@ -229,6 +232,8 @@ function displayEvents(room: Room): MatrixEvent[] {
 export function buildTimeline(c: MatrixClient, room: Room): TimelineItem[] {
   const me = c.getUserId() ?? ''
   const cryptoRunning = Boolean(c.getCrypto())
+  // Messages after this were meant to be end-to-end encrypted.
+  const encryptionSince = room.currentState.getStateEvents(EventType.RoomEncryption, '')?.getTs() ?? Infinity
   const events = displayEvents(room)
 
   // An event is read when someone else's receipt is on it or on anything
@@ -276,6 +281,14 @@ export function buildTimeline(c: MatrixClient, room: Room): TimelineItem[] {
       continue
     }
 
+    // A verification request in a direct message is a notice, not a message.
+    if (type === EventType.RoomMessage && ev.getContent().msgtype === 'm.key.verification.request') {
+      const to = String(ev.getContent().to ?? '')
+      items.push({ kind: 'notice', key, ts, text: `${nameOf(room, ev.getSender() ?? '')} started verifying ${nameOf(room, to)}` })
+      prev = null
+      continue
+    }
+
     const sender = ev.getSender() ?? ''
     const own = sender === me
     const content = ev.getContent<RoomMessageEventContent>()
@@ -301,6 +314,7 @@ export function buildTimeline(c: MatrixClient, room: Room): TimelineItem[] {
       encrypted,
       utd: encrypted ? utdText(ev, cryptoRunning) : undefined,
       e2ee: ev.isEncrypted(),
+      shield: cryptoRunning && !redacted ? shieldOf(c, ev, ts > encryptionSince) : undefined,
       status: status === 'sent' && ev.getId() && readByOthers.has(ev.getId()!) ? 'read' : status,
       first: true,
       last: true,
diff --git a/apps/web/src/matrix/trust.ts b/apps/web/src/matrix/trust.ts
new file mode 100644
index 0000000..f46b275
--- /dev/null
+++ b/apps/web/src/matrix/trust.ts
@@ -0,0 +1,108 @@
+import type { MatrixClient, MatrixEvent } from 'matrix-js-sdk'
+import { EventShieldColour, EventShieldReason } from 'matrix-js-sdk/lib/crypto-api'
+
+// Per-message trust: whether a decrypted message really comes from a
+// session this session trusts. The crypto stack answers asynchronously, so
+// answers are cached per event and the timeline is redrawn when one comes
+// in. A change in anybody's trust throws the cache away.
+
+export interface Shield {
+  /** `warning`: not verified; `danger`: something is wrong with the sender. */
+  tone: 'warning' | 'danger'
+  text: string
+}
+
+const cache = new Map<string, Shield | null>()
+const pending = new Set<string>()
+let changed: () => void = () => undefined
+let generation = 0
+
+/** Called when a shield arrives, to redraw. */
+export function onShieldsChanged(fn: () => void) {
+  changed = fn
+}
+
+/** Forgets every shield: trust changed (a verification, new keys). */
+export function resetShields() {
+  generation++
+  cache.clear()
+  pending.clear()
+  changed()
+}
+
+function reasonText(reason: EventShieldReason | null): Shield {
+  switch (reason) {
+    case EventShieldReason.UNSIGNED_DEVICE:
+      return { tone: 'danger', text: 'Sent from a session its owner hasn’t verified' }
+    case EventShieldReason.UNKNOWN_DEVICE:
+      return { tone: 'danger', text: 'Sent from a session that no longer exists or was never announced' }
+    case EventShieldReason.MISMATCHED_SENDER_KEY:
+    case EventShieldReason.MISMATCHED_SENDER:
+      return { tone: 'danger', text: 'The sender’s keys don’t match: it may not be from them' }
+    case EventShieldReason.VERIFICATION_VIOLATION:
+      return { tone: 'danger', text: 'The sender’s identity changed since you verified them' }
+    case EventShieldReason.AUTHENTICITY_NOT_GUARANTEED:
+      return { tone: 'warning', text: 'Its authenticity can’t be guaranteed on this session (restored from a backup)' }
+    case EventShieldReason.UNVERIFIED_IDENTITY:
+      return { tone: 'warning', text: 'Sent by someone you haven’t verified' }
+    case EventShieldReason.SENT_IN_CLEAR:
+      return { tone: 'danger', text: 'Not encrypted' }
+    default:
+      return { tone: 'warning', text: 'Can’t confirm who sent this' }
+  }
+}
+
+async function compute(c: MatrixClient, ev: MatrixEvent): Promise<Shield | null> {
+  const crypto = c.getCrypto()
+  if (!crypto) return null
+  const info = await crypto.getEncryptionInfoForEvent(ev)
+  if (!info) return null
+  if (info.shieldColour !== EventShieldColour.NONE) {
+    const s = reasonText(info.shieldReason)
+    return info.shieldColour === EventShieldColour.RED ? { ...s, tone: 'danger' } : s
+  }
+  // The crypto stack is quiet about sessions nobody verified. This
+  // session says so: which of the sender's sessions sent it, and is it one
+  // you (or the sender's verified identity) vouch for?
+  const sender = ev.getSender() ?? ''
+  const senderKey = ev.getSenderKey()
+  if (!senderKey) return null
+  if (sender === c.getUserId()) {
+    const own = await crypto.getOwnDeviceKeys()
+    if (own.curve25519 === senderKey) return null
+  }
+  const devices = await crypto.getUserDeviceInfo([sender])
+  const device = [...(devices.get(sender)?.values() ?? [])].find((d) => d.getIdentityKey() === senderKey)
+  if (!device) return null
+  const status = await crypto.getDeviceVerificationStatus(sender, device.deviceId)
+  if (status?.isVerified()) return null
+  return { tone: 'warning', text: sender === c.getUserId() ? 'Sent from one of your sessions you haven’t verified' : 'Sent from a session you haven’t verified' }
+}
+
+/**
+ * The shield a message shows, or undefined for none (or not known yet:
+ * it is worked out in the background and the timeline redrawn).
+ */
+export function shieldOf(c: MatrixClient, ev: MatrixEvent, expectEncrypted: boolean): Shield | undefined {
+  const id = ev.getId()
+  if (!id || ev.status !== null || ev.isRedacted()) return undefined
+  if (!ev.isEncrypted()) {
+    // A plain message sent after the room turned encryption on.
+    return expectEncrypted ? { tone: 'danger', text: 'Not encrypted' } : undefined
+  }
+  if (ev.isDecryptionFailure() || ev.isBeingDecrypted()) return undefined
+  if (cache.has(id)) return cache.get(id) ?? undefined
+  if (!pending.has(id)) {
+    pending.add(id)
+    const gen = generation
+    compute(c, ev)
+      .catch(() => null)
+      .then((s) => {
+        if (gen !== generation) return
+        pending.delete(id)
+        cache.set(id, s)
+        if (s) changed()
+      })
+  }
+  return undefined
+}
diff --git a/apps/web/src/stores/chat.ts b/apps/web/src/stores/chat.ts
index 68e033d..50bf2d8 100644
--- a/apps/web/src/stores/chat.ts
+++ b/apps/web/src/stores/chat.ts
@@ -19,6 +19,7 @@ import {
 import { defineStore } from 'pinia'
 import { computed, ref, shallowRef, watch } from 'vue'
 import { client } from '@/matrix/client'
+import { onShieldsChanged } from '@/matrix/trust'
 
 // The room list and the client's connection state, as plain reactive data
 // derived from the SDK. The SDK's objects change in place and emit events;
@@ -61,6 +62,7 @@ export function describeEvent(ev: MatrixEvent, me: string, room: Room, withSende
   if (type !== EventType.RoomMessage && type !== EventType.Sticker) return null
   if (ev.isRelation('m.replace')) return null
   const content = ev.getContent()
+  if (content.msgtype === 'm.key.verification.request') return 'Verification request'
   let text: string
   switch (content.msgtype) {
     case MsgType.Image:
@@ -196,6 +198,7 @@ export const useChat = defineStore('chat', () => {
     ready.value = c.isInitialSyncComplete()
     syncState.value = c.getSyncState()
     c.on(ClientEvent.Sync, onSync)
+    onShieldsChanged(bump)
     for (const e of [
       ClientEvent.Room,
       ClientEvent.DeleteRoom,
@@ -303,14 +306,9 @@ export const useChat = defineStore('chat', () => {
     }
     // Fails early with a clear error when the person doesn't exist.
     await c.getProfileInfo(userId)
-    // End-to-end encrypted when the other person has a session that can
-    // read it: encrypting to nobody would only lock them out.
-    let encrypt = false
-    const crypto = c.getCrypto()
-    if (crypto) {
-      const devices = await crypto.getUserDeviceInfo([userId], true).catch(() => null)
-      encrypt = (devices?.get(userId)?.size ?? 0) > 0
-    }
+    // Always end-to-end encrypted while this session can encrypt. Someone
+    // with no session yet reads what is sent after they sign in.
+    const encrypt = Boolean(c.getCrypto())
     const res = await c.createRoom({
       is_direct: true,
       invite: [userId],
@@ -322,6 +320,18 @@ export const useChat = defineStore('chat', () => {
     return res.room_id
   }
 
+  /** A room you and the person are both in: your direct message first, else the smallest. */
+  function sharedRoomWith(userId: string): string | undefined {
+    const c = client()
+    const joined = (r: Room | null) => r?.getMyMembership() === KnownMembership.Join && r.getMember(userId)?.membership === KnownMembership.Join
+    const content = (c.getAccountData(EventType.Direct)?.getContent() ?? {}) as Record<string, string[]>
+    for (const roomId of content[userId] ?? []) if (joined(c.getRoom(roomId))) return roomId
+    return c
+      .getRooms()
+      .filter(joined)
+      .sort((a, b) => a.getJoinedMemberCount() - b.getJoinedMemberCount())[0]?.roomId
+  }
+
   async function join(idOrAlias: string): Promise<string> {
     const room = await client().joinRoom(idOrAlias.trim())
     return room.roomId
@@ -366,6 +376,7 @@ export const useChat = defineStore('chat', () => {
     bump,
     createRoom,
     startDirect,
+    sharedRoomWith,
     join,
     acceptInvite,
     leave,
diff --git a/apps/web/src/stores/security.ts b/apps/web/src/stores/security.ts
index f54bcea..03f073f 100644
--- a/apps/web/src/stores/security.ts
+++ b/apps/web/src/stores/security.ts
@@ -11,10 +11,14 @@ import { client } from '@/matrix/client'
 import {
   enableBackupIfPossible,
   encryptionStatus,
+  isSettingUp,
   verifyDevice,
   verifyOwnSession,
+  verifyUserInRoom,
   type EncryptionStatus,
 } from '@/matrix/crypto'
+import { resetShields } from '@/matrix/trust'
+import { useChat } from '@/stores/chat'
 
 // End-to-end encryption as the views see it: whether this session is
 // verified, the key backup, and the one verification on screen at a time,
@@ -32,7 +36,8 @@ export const useSecurity = defineStore('security', () => {
   let again = false
 
   async function refresh() {
-    if (!attached?.getCrypto()) return
+    // During setup the dialog refreshes once it is done.
+    if (!attached?.getCrypto() || isSettingUp()) return
     // One refresh at a time; changes during one ask for another after it.
     if (refreshing) {
       again = true
@@ -49,6 +54,7 @@ export const useSecurity = defineStore('security', () => {
 
   function changed() {
     version.value++
+    resetShields()
     void refresh()
   }
 
@@ -120,5 +126,15 @@ export const useSecurity = defineStore('security', () => {
     show(await verifyDevice(userId, deviceId))
   }
 
-  return { status, request, version, attach, refresh, dismiss, verifyThisSession, verifySession }
+  /**
+   * Verifies a person's identity in a room you are both in: your direct
+   * message, else the smallest room you share, else a new direct message
+   * (the request waits there until they accept the invite).
+   */
+  async function verifyUser(userId: string) {
+    const roomId = useChat().sharedRoomWith(userId) ?? (await useChat().startDirect(userId))
+    show(await verifyUserInRoom(userId, roomId))
+  }
+
+  return { status, request, version, attach, refresh, dismiss, verifyThisSession, verifySession, verifyUser }
 })
diff --git a/apps/web/src/stores/session.ts b/apps/web/src/stores/session.ts
index 6bb5cfa..e649ff2 100644
--- a/apps/web/src/stores/session.ts
+++ b/apps/web/src/stores/session.ts
@@ -2,7 +2,8 @@ import { HttpApiEvent, MatrixError, type AuthDict, type LoginResponse, type Regi
 import { defineStore } from 'pinia'
 import { computed, ref } from 'vue'
 import { config } from '@/config'
-import { anonymousClient, client, destroyClient, startClient, stopClient, type Credentials } from '@/matrix/client'
+import { anonymousClient, client, destroyClient, newStorageKey, startClient, stopClient, type Credentials } from '@/matrix/client'
+import { cryptoDatabasePrefix } from '@/matrix/crypto'
 import { clearMediaCache } from '@/matrix/media'
 
 // The person's Matrix session. It is kept in localStorage while "Stay
@@ -25,6 +26,22 @@ function load(): Credentials | null {
   return null
 }
 
+/** The crypto stores of the sessions this browser has credentials for, in either storage. */
+export function savedCryptoStores(): string[] {
+  const out: string[] = []
+  for (const store of [localStorage, sessionStorage]) {
+    try {
+      const raw = store.getItem(storageKey)
+      if (!raw) continue
+      const c = JSON.parse(raw) as Credentials
+      if (c.userId && c.deviceId) out.push(cryptoDatabasePrefix(c.userId, c.deviceId))
+    } catch {
+      // Unreadable: nothing to keep.
+    }
+  }
+  return out
+}
+
 function save(c: Credentials | null, remember: boolean) {
   for (const store of [localStorage, sessionStorage]) {
     try {
@@ -127,6 +144,8 @@ export const useSession = defineStore('session', () => {
       userId: res.user_id,
       deviceId: res.device_id,
       accessToken: res.access_token,
+      // Kept only for the tab: its encryption keys are unreadable once it closes.
+      storageKey: keep ? undefined : newStorageKey(),
     }
     save(creds, keep)
     await begin(creds)
diff --git a/apps/web/src/views/RoomView.vue b/apps/web/src/views/RoomView.vue
index 9870df0..fd2f254 100644
--- a/apps/web/src/views/RoomView.vue
+++ b/apps/web/src/views/RoomView.vue
@@ -9,13 +9,16 @@ import RoomTimeline from '@/components/RoomTimeline.vue'
 import { drafts } from '@/lib/drafts'
 import { errorMessage, formatBytes } from '@/lib/format'
 import { client, cryptoError } from '@/matrix/client'
+import { acceptIdentity, identityWarnings, withdrawVerification, type IdentityWarning } from '@/matrix/crypto'
 import { sendFile, sendText } from '@/matrix/send'
 import { useChat } from '@/stores/chat'
+import { useSecurity } from '@/stores/security'
 import { useToasts } from '@/stores/toasts'
 
 const props = defineProps<{ roomId: string }>()
 
 const chat = useChat()
+const security = useSecurity()
 const toasts = useToasts()
 const router = useRouter()
 const me = client().getUserId() ?? ''
@@ -49,6 +52,44 @@ const canSend = computed(() => {
 
 const infoOpen = ref(false)
 
+// Someone in an encrypted room whose identity changed: said before you
+// write to them, until you acknowledge it.
+const warnings = ref<IdentityWarning[]>([])
+let warningsRun = 0
+watch(
+  () => [encrypted.value, memberCount.value, security.version, props.roomId] as const,
+  async () => {
+    const run = ++warningsRun
+    const r = room.value
+    if (!encrypted.value || !r || !chat.canEncrypt) {
+      warnings.value = []
+      return
+    }
+    const ids = r.getJoinedMembers().map((m) => m.userId).slice(0, 500)
+    const found = await identityWarnings(ids).catch(() => [])
+    if (run === warningsRun) warnings.value = found
+  },
+  { immediate: true },
+)
+const warning = computed(() => warnings.value[0])
+const warningName = computed(() => (warning.value ? (room.value?.getMember(warning.value.userId)?.name ?? warning.value.userId) : ''))
+const acking = ref(false)
+async function ackWarning(verifyAgain = false) {
+  const w = warning.value
+  if (!w) return
+  acking.value = true
+  try {
+    if (verifyAgain) await security.verifyUser(w.userId)
+    else if (w.kind === 'verifiedReset') await withdrawVerification(w.userId)
+    else await acceptIdentity(w.userId)
+    warnings.value = warnings.value.filter((x) => x.userId !== w.userId)
+  } catch (e) {
+    toasts.error(errorMessage(e))
+  } finally {
+    acking.value = false
+  }
+}
+
 const text = ref(drafts.get(props.roomId) ?? '')
 watch(text, (v) => (v ? drafts.set(props.roomId, v) : drafts.delete(props.roomId)))
 
@@ -251,6 +292,23 @@ const placeholder = computed(() => `Message ${summary.value?.name ?? 'this room'
             <span class="caption text-ink-muted tabular-nums">{{ u.total ? Math.round((u.loaded / u.total) * 100) : 0 }}%</span>
           </div>
 
+          <WBanner
+            v-if="warning && !cryptoMissing"
+            :tone="warning.kind === 'verifiedReset' ? 'danger' : 'warning'"
+            :title="warning.kind === 'verifiedReset' ? `${warningName}’s identity changed since you verified them` : `${warningName}’s identity changed`"
+          >
+            <template v-if="warning.kind === 'verifiedReset'">
+              Their sessions are no longer trusted. If they didn’t reset their encryption themselves, someone may be pretending to be them.
+              Verify them again, or stop requiring them to be verified.
+            </template>
+            <template v-else>They reset their encryption, or signed in somewhere new without verifying. Check with them if you weren’t expecting it.</template>
+            <span class="mt-2 flex flex-wrap gap-2">
+              <WButton v-if="warning.kind === 'verifiedReset'" size="sm" variant="primary" :disabled="acking" @click="ackWarning(true)">
+                Verify {{ warningName }}
+              </WButton>
+              <WButton size="sm" :loading="acking" @click="ackWarning()">{{ warning.kind === 'verifiedReset' ? 'Withdraw verification' : 'OK' }}</WButton>
+            </span>
+          </WBanner>
           <WBanner v-if="cryptoMissing" tone="warning" title="End-to-end encryption didn’t start">
             This browser can’t read or send messages in this room. Reload the page to try again{{ cryptoError() ? ` (${cryptoError()})` : '' }}.
           </WBanner>
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 7870a68..8311747 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -68,12 +68,18 @@ importers:
       '@warp/ui':
         specifier: workspace:*
         version: link:../ui
+      jsqr:
+        specifier: 1.4.0
+        version: 1.4.0
       matrix-js-sdk:
         specifier: ^44.0.0
         version: 44.0.0
       pinia:
         specifier: ^3.0.3
         version: 3.0.4(typescript@5.9.3)(vue@3.5.44(typescript@5.9.3))
+      qrcode-generator:
+        specifier: 1.4.4
+        version: 1.4.4
       vue:
         specifier: ^3.5.22
         version: 3.5.44(typescript@5.9.3)
@@ -670,6 +676,9 @@ packages:
     resolution: {integrity: sha512-AC/7JofJvZGrrneWNaEnJeOLUx+JlGt7tNa0wZiRPT4MY1wmfKjt2+6O2p2uz2+skll8OZZmJMNqeke7kKbNgQ==}
     hasBin: true
 
+  jsqr@1.4.0:
+    resolution: {integrity: sha512-dxLob7q65Xg2DvstYkRpkYtmKm2sPJ9oFhrhmudT1dZvNFFTlroai3AWSpLey/w5vMcLBXRgOJsbXpdN9HzU/A==}
+
   lightningcss-android-arm64@1.32.0:
     resolution: {integrity: sha512-YK7/ClTt4kAK0vo6w3X+Pnm0D2cf2vPHbhOXdoNti1Ga0al1P4TBZhwjATvjNwLEBCnKvjJc2jQgHXH0NEwlAg==}
     engines: {node: '>= 12.0.0'}
@@ -798,6 +807,9 @@ packages:
     resolution: {integrity: sha512-zkd+e9S1AQHhmaBKye9zlFHWjOwVgqXl1q3ECYy8561K7qxR2cREf/STLskulBFd78k6AOFeA+ff1TtEzk9bAA==}
     engines: {node: ^10 || ^12 || >=14}
 
+  qrcode-generator@1.4.4:
+    resolution: {integrity: sha512-HM7yY8O2ilqhmULxGMpcHSF1EhJJ9yBj8gvDEuZ6M+KGJ0YY2hKpnXvRD+hZPLrDVck3ExIGhmPtSdcjC+guuw==}
+
   rfdc@1.4.1:
     resolution: {integrity: sha512-q1b3N5QkRUWUl7iyylaaj3kOpIT0N2i9MqIEQXP73GVsN9cw3fdx8X63cEmWhJGi2PPCF23Ijp7ktmd39rawIA==}
 
@@ -1355,6 +1367,8 @@ snapshots:
 
   jiti@2.7.0: {}
 
+  jsqr@1.4.0: {}
+
   lightningcss-android-arm64@1.32.0:
     optional: true
 
@@ -1462,6 +1476,8 @@ snapshots:
       picocolors: 1.1.1
       source-map-js: 1.2.2
 
+  qrcode-generator@1.4.4: {}
+
   rfdc@1.4.1: {}
 
   rollup@4.64.9: