diff --git a/src/features/nostr/sign.ts b/src/features/nostr/sign.ts
new file mode 100644
index 000000000..5a9b72082
--- /dev/null
+++ b/src/features/nostr/sign.ts
@@ -0,0 +1,52 @@
+import {
+  type Event,
+  type EventTemplate,
+  generatePrivateKey,
+  getPublicKey as _getPublicKey,
+  finishEvent,
+  nip04 as _nip04,
+} from 'nostr-tools';
+
+/** localStorage key for the Nostr private key (if not using NIP-07). */
+const LOCAL_KEY = 'soapbox:nostr:privateKey';
+
+/** Get the private key from the browser, or generate one. */
+const getPrivateKey = (): string => {
+  const local = localStorage.getItem(LOCAL_KEY);
+
+  if (!local) {
+    const key = generatePrivateKey();
+    localStorage.setItem(LOCAL_KEY, key);
+    return key;
+  }
+
+  return local;
+};
+
+/** Get the user's public key from NIP-07, or generate one. */
+async function getPublicKey(): Promise<string> {
+  return window.nostr ? window.nostr.getPublicKey() : _getPublicKey(getPrivateKey());
+}
+
+/** Sign an event with NIP-07, or the locally generated key. */
+async function signEvent<K extends number>(event: EventTemplate<K>): Promise<Event<K>> {
+  return window.nostr ? window.nostr.signEvent(event) as Promise<Event<K>> : finishEvent(event, getPrivateKey()) ;
+}
+
+/** Crypto function with NIP-07, or the local key. */
+const nip04 = {
+  /** Encrypt with NIP-07, or the local key. */
+  encrypt: async (pubkey: string, content: string) => {
+    return window.nostr?.nip04
+      ? window.nostr.nip04.encrypt(pubkey, content)
+      : _nip04.encrypt(getPrivateKey(), pubkey, content);
+  },
+  /** Decrypt with NIP-07, or the local key. */
+  decrypt: async (pubkey: string, content: string) => {
+    return window.nostr?.nip04
+      ? window.nostr.nip04.decrypt(pubkey, content)
+      : _nip04.decrypt(getPrivateKey(), pubkey, content);
+  },
+};
+
+export { getPublicKey, signEvent, nip04 };
\ No newline at end of file