OTP Auth

OTP (one-time password) Auth enables a user to authenticate their Turnkey account with an email or phone number via a 6 digit one time password. Similar to email auth, the user is granted an expiring API key that is stored in memory within an iframe. This expiring API key can then be used by the user to access their wallet, similar to a session key. An example utilizing OTP Auth for an organization can be found in our SDK repo here.

Mechanism

OTP Auth uses two activities: INIT_OTP_AUTH sends a 6-digit OTP code to a specified phone number or email, and OTP_AUTH to verify the code. Upon successful verification, OTP_AUTH returns the encrypted API key credential in the activity result. This credential is then available for stamping (authenticating) requests on the client side.

User Experience

OTP Auth starts with a new activity posted to Turnkey. This activity has the type ACTIVITY_TYPE_INIT_OTP_AUTH and takes the following as parameters:

• otpType: specifiy delivery mechanism "OTP_TYPE_SMS" or "OTP_TYPE_EMAIL"
• contact: the email or phone number of the user who would like to authenticate. This contact must be already attached to the user in organization data (i.e., previously approved by the user). This prevents malicious account takeover. If you try to pass a different email address or phone number, the activity will fail.
• emailCustomization: optional parameters for customizing emails. If not provided, the default email will be used. For more info, see the integration guide.

This activity generates a 6 digit OTP, and sends it as an email or SMS

This activity returns an otpId in the result to be used in the following ACTIVITY_TYPE_OTP_AUTH to verify the 6 digit code which takes the following as parameters:

• otpId: ID representing the result of an ACTIVITY_TYPE_INIT_OTP_AUTH
• otpCode: 6 digit OTP code sent out to a user's contact (email or SMS)
• targetPublicKey: the public key to which the auth credential is encrypted (more on this later)
• apiKeyName: an optional name for the API Key. If none is provided, we will default to OTP Auth - <Timestamp>
• expirationSeconds: an optional window (in seconds) indicating how long the API Key should last. Default to 15 minutes.
• invalidateExisting: an optional boolean used to invalidate all other previously generated OTP Auth API keys

Initiating OTP Auth for both "OTP_TYPE_SMS" and "OTP_TYPE_EMAIL" requires proper permissions via policies or being a parent organization. See Authorization for more details.

Authorization

Authorization for OTP auth is based on our usual activity authorization: our policy engine controls who can and cannot execute auth-related activities.

• ACTIVITY_TYPE_OTP_AUTH can be performed by the root user or by any user in an organization if authorized by policy, but only if the feature is enabled. The activity can target any user in this organization or any sub-organization user. The activity will fail if a parent user tries to perform OTP auth for a sub-organization which has opted out of this feature.

Opting out of OTP auth

Similar to email recovery and email auth, depending on your threat model, it may be unacceptable to rely on an email or phone number as an authentication factor. We envision this to be the case when an organization has a mature set of root users with multiple authenticators, or when a sub-organization "graduates" from one to many redundant passkeys or API keys. When you're ready, you can disable OTP auth with ACTIVITY_TYPE_REMOVE_ORGANIZATION_FEATURE (see Remove Organization Feature). The feature name to remove is FEATURE_NAME_OTP_EMAIL_AUTH for OTP email and FEATURE_NAME_SMS_AUTH for OTP SMS.

If you never want to have OTP email/SMS auth enabled for sub-organizations, our CREATE_SUB_ORGANIZATION activity takes disableOtpEmailAuth and disableSmsAuth booleans in its parameters. Set them to true and the sub-organization will be created without the organization feature.

Mechanism and cryptographic details

Note: if the following section looks familiar, it is! It shares similar cryptographic innerworkings to Email Recovery and Email Auth.

Turnkey's OTP auth doesn't send unencrypted tokens via the activity result. This ensures no man-in-the-middle attack can happen: even if the content of the activity result is leaked, an attacker wouldn't be able to decrypt the auth credential. The following diagram summarizes the flow (Same as Email auth):

Our OTP auth flow works by anchoring auth in a target encryption key (TEK). This target encryption key is a standard P-256 key pair and can be created in many ways: completely offline, or online inside of script using the web crypto APIs.

The public part of this key pair is passed as a parameter inside of a signed OTP_AUTH activity. The signature on the activity has to come from a user who is authorized to initiate OTP auth.

Our enclave creates a fresh P256 key pair ("auth credential") and encrypts the private key to the recovering user's TEK using the Hybrid Public Key Encryption standard, also known as HPKE or RFC 9180.

Once the encrypted auth credential is received via the activity result, it's decrypted where the target public key was originally created. The auth credential is then ready to be used to sign an activity, which is then submitted to Turnkey.

Implementation notes

Users currently have a limit of 10 long-lived API keys, and 10 expiring API keys. In the case that the limit of expiring API keys is breached, the oldest (by creation date) will be discarded.

NOTE: feature must be enabled. For top-level orgs, by default, OTP auth is not enabled. It must be enabled via the ACTIVITY_TYPE_SET_ORGANIZATION_FEATURE activity. Here's an example for OTP email auth, using our CLI:

turnkey request --host api.turnkey.com --path /public/v1/submit/set_organization_feature --body '{
        "timestampMs": "'"$(date +%s)"'000",
        "type": "ACTIVITY_TYPE_SET_ORGANIZATION_FEATURE",
        "organizationId": "<YOUR-ORG-ID>",
        "parameters": {
                "name": "FEATURE_NAME_OTP_EMAIL_AUTH"
        }
}' --organization <YOUR-ORG-ID>

Suborgs have OTP Auth enabled for both SMS and email as a feature by default. It can be conveniently disabled during creation, using the CreateSubOrganizationIntentV7 activity parameter disableOtpEmailAuth and disableSmsAuth.