Sign in with a passkey. Get a Nano purse.

The next time

• One prompt. "Use my passkey" asks your device once and opens the same purse. A browser that still holds the purse signs in with its purse tile, and the device is not asked.
• "I have a passkey" or "Make a new one". Where a page is about to make a purse, and this browser has not used a passkey yet, it asks this first. A second passkey is a second, empty purse, so a person who has one must not make one by mistake. Where the site makes new passkey purses, a third button sits under the two, here and under "Use my passkey" and "Make a passkey" in the sign-in sheet: "Make a purse in this browser only". That purse has no passkey: its key stays in this browser. It stops one time at "Back up your purse's code", and the page still reminds you until you save the code.

Where is my key?

• On your device. The purse's key is made there and used there. It is never sent to the site.
• With your passkey. Apple, Google or a password manager can keep the passkey and copy it to your other devices. By the design, the purse comes with it: the same passkey, the same purse. A passkey does not cross from one maker to another by itself: an iPhone's passkey reaches a Windows PC by a QR scan with the phone, or through a password manager. not tested by us yet
• Not with the site. No password table, no key and no copy of the purse. A stolen database holds nothing that opens a purse.

One site, one purse

A passkey works only on the site that made it. So a person has a different purse, with a different Nano address, on each site that uses this kit. Two sites cannot link one person by an address. Each purse is its own small wallet: money in one is not in the other.

Is it safe?

It is safer than a password, and it is not magic. Here is what this design stops, and what it does not. Treat a purse in a browser like the cash in your pocket: enough to play and to pay, not your savings.

Keep your device clean

The purse is as safe as the device it is on. Seven habits do most of the work.

1. Update

   Keep the system and the browser up to date.

2. Few extensions

   Keep only the browser extensions you need, from makers you know.

3. A screen lock

   A face, a finger or a PIN on every device that has your passkey.

4. Passkey sync on

   Let your phone maker or password manager keep the passkey, so a lost phone is not a lost purse. A passkey on a security key stays on that key.

5. The recovery code on paper

   Write it down once and keep it away from the device. It is the only other way in.

6. Play money only

   Keep small amounts in a browser purse. Keep larger amounts in a wallet app or a hardware wallet.

7. Check the address

   Look at the address bar before you tap. The real site, with the lock, and no other.

For your site: ten lines

Your page asks for a passkey on your own domain, gets a Nano address and a signature, and your server checks that one signature. You store an address. You never store a key.

import { signinMessage } from "@nano133/signin/message";          // safe for a browser
import { checkSignatureSignin } from "@nano133/signin/signature";  // your server

// In the browser, on a tap: the purse from the passkey signs one short message.
const at = Date.now();
const message = signinMessage("shop.example", address, at);  // your own domain is in the text
const signature = purse.sign(message);                       // the purse from the passkey: not in the package yet

// Send three short values to your server:
await fetch("/signin/signature", { method: "POST", body: JSON.stringify({ address, at, signature }) });

// On your server: one check, no secret and no user table.
const account = await checkSignatureSignin({ domain: "shop.example", useOnce }, { address, at, signature });

A sketch of the kit's code. nano133 runs this design in its own sign-in sheet. The two functions with a name here are in @nano133/signin today, from 0.2.1. The purse from a passkey is not in the package yet.

• No server secret. Your server checks one signature. It needs no key of its own and no table of passwords.
• Your domain, and all of it. A passkey belongs to your domain, and any page on a subdomain of it can ask for that passkey. So every subdomain must be your own.
• Where the browser cannot do it. Some older phones and browsers cannot make a purse from a passkey. A password manager's extension can answer in a form that the page does not read: one such form (a list of 32 numbers) is read, others are refused. A browser that reports the function can still fail. The page then says so in plain words and makes nothing weaker in its place. You can still sign in with a wallet that signs, or use a purse that lives in this browser.