StellarExpert ID – Single-Sign-On App and Tx Signer for Stellar Network

StellarExpertID provides a safe and reliable way to use your Stellar accounts without trusting anyone with your secret key. All sensitive data is encrypted with your password and securely stored in the browser.

Key features

• Secure key management – your secret key is never exposed to third-party services.
• Secure transaction signing – transactions are signed without exposing a secret key.
• SEP-0007 compatible – can be used to handle "web+stellar" links.
• Web apps Single Sign-On – login to third-party websites, just like with Google or Facebook OAuth.
• Two-factor authorization support – provides another level of protection for your accounts.
• Digital identity – associate a nickname, email, or avatar with your account address (or leave it blank if you prefer to stay incognito).
• Multi-account support – use multiple accounts and switch them when you need it.
• Message signing tools – sign and verify arbitrary data with your private keys.
• Inflation voting – vote for inflation pools with a single button click without worries for your funds' safety.
• Federation support – make use of a human-friendly address for your account.
• Works everywhere – the same account operates seamlessly via desktops, smartphones, and tablets.

Intents

There are 4 main groups of intents:

1. Request transaction signing. The signer app prepares and signs a transaction which then can be returned to the initiator website or submitted directly to the network.
2. Request specific action. Either "transfer funds", "vote for inflation pool", or "establish a trustline". Each action is effectively a simplified wrapper for the transaction signing request. No custom logic or even JS SDK is required on the initiator side.
3. Request information. The website may request a user's personal info (email, avatar) or Stellar account public key.
4. Request cryptographic signature of the arbitrary data. The website may request a crypto signature to verify a keypair ownership (authentication, secure messages exchange etc).

Authorization flows

The signer supports two authorizaton flows: an implicit flow and callback flow.

Implicit flow

A popup window with request details is shown each time an initiator website requests the action.

1. A user invokes some action on the third-party website (a wallet, DEX interface, inflation pool etc). Let's say, he wants to create an offer.
2. The website prepares the requested transaction and it's XDR representation in base64 format.
3. The website initiates the intent (see intent list in the project description) using js module that provides an interface for all supported intents.
4. The interface module opens a new pop-up window pointing to id.stellar.expert. All intent parameters are serialized and transmitted in a form of GET parameters. So the full URL will look like https://id.stellar.expert/confirm?intent=tx&network=testnet&xdr=AAAAALPZeTF82....
5. Signer application reads parameters from the URL and asks the user for a confirmation.
6. The user chooses a keypair from the list of stored accounts (or adds a new one) and confirms the action.
7. The signer app signs the transaction the same way any other wallet do it.
8. The signed transaction is serialized into XDR as TransactionEnvelope and transmitted back to the opener site in base64 encoding via the built-in browser postMessage mechanism.
9. The third-party website receives a signed transaction envelope and may choose either to submit it to the network or store somewhere in case if the tx needs more signatures or if it has time bounds set.

Intent confirmation dialog always contains extended request information, including intent description (like "Sign transaction"), initiator website ("origin: example.com"), risk level ("high", "medium", or "low"), information about personal data disclosure (only for personal_info intent), and safety status ("safe" or "potentially unsafe"). Intent-specific details allow a user to review the request before confirmation. For instance, a dialog with sing_tx intent displays full transaction information including all meaningful properties and the list of operations in a human-friendly format adapted for the ordinary users.

Callback flow

The callback flow supports Stellar SEP-0007 link format.
Instead of showing a popup authorization dialog, it redirects the browser to the signer page.
A signed transaction can be either submitted to the network or returned to the specified callback URL via POST request.

Technical details

The project consists of three modules:

• The signer website itself – provides a user-friendly interface for key management and operation intents.
• Client intent module – JS library that simplifies StellarExpertId integration and usage.
• Server-side vault – a simple server that provides API for encrypted credentials storage and 2FA verification.

(Server-side vault storage option is temporarily disabled).

The intent library supports the following actions ("intents"):

• signTransaction(xdr, options) – requests transaction signing (returns signed transaction envelope, can be used for multi-sig).
• pay(destination, amount, asset_code, asset_issuer, memo, memo_type, options) – requests a payment.
• trust(asset_code, asset_issuer, limit, options) – requests inflation pool voting.
• inflationVote(inflationDestination, options) – requests inflation pool voting.
• signMessage(msg) – requests arbitrary data signing.
• verifyMessage(msg, signature) – requests arbitrary data signature verification.
• requestAddress() – requests account public key (for basic web authentication).
• authenticate() – requests user identity verification (for SSO login).
• requestPersonalInfo() – requests personal info access (avatar, nickname etc).

Available transaction intent options:

• network – stellar account network identifier ("public", "testnet") or private network passphrase.
• horizon – the url of a Stellar Horizon server (for transactions only).
• prepare – if set, the signer will return a signed tx envelope instead of submitting it to the Horizon server.

Formal intent data contracts can be found here.

"web+stellar" links

In order to set up this application as a signer for "web+stellar" links as described in SEP-0007, you may either use navigator.registerProtocolHandler() (works in Chrome and Firefox) or configure the protocol binding manually.

navigator.registerProtocolHandler('web+stellar', 
    'https://id.stellar.expert/confirm?encoded=%s', 
    'StellarExpertId signer')

Please note: it's a developer preview software version, do not store your real Stellar account secret keys here.

Secret key storage options

Choose security options that suit you.

Multi-login with Two-factor authorization

Allowing this feature increases security and simplify your account usage across all your devices and browsers. Your secret key is encrypted with your password in the browser and securely stored on our servers. We do not have access to your account.

Account log-in and all subsequent actions are protected with 2FA TOTP authorization.

This feature works with 2FA applications like Google Authenticator, Free OTP, or Authy.

Browser-only storage with password protection

Credentials are encrypted with your password and stored in the browser. Nobody except you can obtain access to your account.

Account log-in and all subsequent actions require your password.

Paranoid mode

StellarExpert ID never stores your credentials or any other info on our servers, nor in the browser. Nevertheless, you still can sign transactions and use other features providing your secret key to confirm all actions.

Account log-in and all subsequent actions require your secret key.

Next steps

Once the interfaces and modules are stable and documented, I'm going to add support of other security-related applications, like Ledger Nano support, StellarGuard by Paul, CosmicLink by MisterTicot etc.

Liabilities and trust

Originally this application was designed as a part of StellarExpert, but the more I think about it, the more I convince myself that it should be maintained and operated by the reliable public entity. Why would you trust some random anonymous guy from the internet?

Hence I decided to ask SDF to maintain and host the application. I'm ready to transfer the repositories, all explicit and implicit copyrights, claiming only as much as a reference in the readme/license repository file. The reasons behind this decision:

• Safe development. All pull requests will be reviewed by SDF maintainers, and we all know that Bartek is a top-notch security specialist.
• Trusted infrastructure. The application will be deployed and administrated by guys who support Core nodes and publicly available Horizon.
• Trusted entity. I think we all can agree that SDF is the most trusted entity across Stellar Network as it runs the crucial part of the network and holds the largest part of all available Lumens.

If SDF itself runs the application under its own brand (say, "StellarID"), it will give green light to all developers and users. We all can be sure that guys from SDF won't modify sources to steal users' private keys and everyone will be able to participate in the process. As for me, I'll keep contributing to the project with pull-requests.

So here I'm asking for the opinion of Stellar community. If you think that such an application will be useful, I will contact SDF with this matter.

• The project demo is available here.
• Source code on GitHub.
• Issue tracker.

Will be glad to hear any questions and feedback.

dzham No, it works like Google/Twitter/Facebook OAuth.
Once you have initiated an action, a new browser window is open and the user can approve or reject the action.

dzham I'm going to parse the message. If it is a valid tx xdr, the signer will return an error.

Something like

try {
  new Transaction(xdr)
  // a valid transaction wouldn't throw an error
  return Promise.reject(new Error('Potentially malicious message.'))
}
catch(e) {
  return Promise.resolve(xdr)
}