Only people you know get to buzz your phone

A NIP-17 wrap is signed by a throwaway key with the sender sealed under
two layers of nip44, so no server can filter DMs by who sent them. The
notifier now ships the wrap inside the push payload and the service
worker opens it locally: a message from someone you follow arrives with
their name on it, a stranger's is dropped, and your own sent-copy — every
DM is wrapped to the sender too — no longer notifies you about what you
just typed.

That needs the nostr identity key in the worker's IndexedDB, which
dm-inbox.js states plainly: for a seed-derived identity it is a second
copy of a key localStorage's seed already yields, and it exists only to
keep strangers out. A remote signer never hands its key over, so those
wallets store no secret and keep getting unfiltered notifications rather
than silence.

Silence is always the riskier failure here, so the rule leans the other
way whenever it isn't sure: a wrap we can't open notifies, an account
with no contact list published notifies (otherwise a new user's welcome
message would vanish), and anyone you already have a thread with counts
as known whether or not you follow them. The server-side DM cooldown
drops to a second — with the device discarding pushes, a throttle there
would let a discarded one swallow the message behind it.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Wvj4aoeMZwA7VUGdJP9Swi

1 files changed, 115 insertions, 0 deletions

diff --git a/src/dm-inbox.js b/src/dm-inbox.js
new file mode 100644
index 0000000..a91a8e0
--- /dev/null
+++ b/src/dm-inbox.js
@@ -0,0 +1,115 @@
+// What the service worker needs to tell a friend's DM from a stranger's.
+//
+// A NIP-17 wrap is signed by a throwaway key and the sender's identity sits
+// under two layers of nip44, so no server can filter DMs by who sent them —
+// only the recipient's own key can open one. The notifier therefore ships the
+// wrap inside the push payload and the decision happens here, on the device.
+//
+// THREAT MODEL, stated plainly. This record holds the nostr identity secret,
+// so anything with same-origin script access or a stolen unlocked device can
+// read every DM this account can read. That is not a new exposure for a
+// seed-derived identity — localStorage already holds the seed that key comes
+// from — but it is a second copy, and it exists only to keep strangers from
+// buzzing the phone. A remote signer (bunker/extension) never hands over its
+// key: those wallets store no secret here and fall back to a generic
+// notification instead of a filtered one.
+
+import { unwrapDM } from './dm.js';
+
+const DB = 'coinos-dm-inbox';
+const STORE = 'inbox';
+const VERSION = 1;
+
+function openDb() {
+  return new Promise((resolve, reject) => {
+    if (typeof indexedDB === 'undefined') return reject(new Error('IndexedDB unavailable'));
+    const req = indexedDB.open(DB, VERSION);
+    req.onupgradeneeded = () => {
+      const db = req.result;
+      if (!db.objectStoreNames.contains(STORE)) db.createObjectStore(STORE);
+    };
+    req.onsuccess = () => resolve(req.result);
+    req.onerror = () => reject(req.error);
+  });
+}
+
+async function tx(mode, fn) {
+  const db = await openDb();
+  try {
+    return await new Promise((resolve, reject) => {
+      const t = db.transaction(STORE, mode);
+      const s = t.objectStore(STORE);
+      let out;
+      Promise.resolve(fn(s)).then((v) => { out = v; }).catch(reject);
+      t.oncomplete = () => resolve(out);
+      t.onerror = () => reject(t.error);
+      t.onabort = () => reject(t.error);
+    });
+  } finally { db.close(); }
+}
+
+// One record per wallet: { sk, pubkey, follows: [hex], names: { hex: name } }.
+// `sk` is null when the identity lives behind a remote signer.
+export async function saveInbox(walletKey, rec) {
+  return tx('readwrite', (s) => { s.put(rec, walletKey); });
+}
+export async function clearInbox(walletKey) {
+  return tx('readwrite', (s) => { s.delete(walletKey); });
+}
+export async function allInboxes() {
+  try {
+    return await tx('readonly', (s) => new Promise((res, rej) => {
+      const out = [];
+      const cur = s.openCursor();
+      cur.onsuccess = () => {
+        const c = cur.result;
+        if (!c) return res(out);
+        out.push(c.value);
+        c.continue();
+      };
+      cur.onerror = () => rej(cur.error);
+    }));
+  } catch { return []; }
+}
+
+const unhex = (h) => Uint8Array.from(h.match(/.{2}/g).map((b) => parseInt(b, 16)));
+
+// Open a wrap against every identity we hold a key for. Returns
+// { author, followed, name, mine } for the first one that opens it, or null
+// if none can — which includes every remote-signer wallet, so a null means
+// "we don't know", never "it's a stranger".
+export async function classifyDm(wrap, inboxes) {
+  for (const rec of inboxes) {
+    if (!rec || !rec.sk) continue;
+    let sk;
+    try { sk = unhex(rec.sk); } catch { continue; }
+    const opened = await unwrapDM(wrap, sk);
+    if (!opened) continue;
+    const author = opened.author;
+    return {
+      author,
+      mine: author === rec.pubkey,
+      followed: (rec.follows || []).includes(author),
+      // Someone you're already talking to is not a stranger, whether or not
+      // you ever followed them.
+      known: (rec.known || []).includes(author),
+      // No contact list published at all: there's nothing to filter against,
+      // and silence would be worse than noise.
+      hasList: !!rec.hasList,
+      name: (rec.names || {})[author] || null,
+      content: opened.rumor && opened.rumor.kind === 14 ? opened.rumor.content : '',
+    };
+  }
+  return null;
+}
+
+// Should this DM interrupt someone? Our own sent-copy never should — every
+// NIP-17 message is wrapped to the sender too, and being notified about what
+// you just typed is pure noise. Anything we couldn't open stays notifiable:
+// better a generic buzz than a silent drop.
+export function shouldNotifyDm(verdict) {
+  if (!verdict) return true;
+  if (verdict.mine) return false;
+  if (verdict.followed || verdict.known) return true;
+  return !verdict.hasList;
+}