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The Internet Identity Specification

Introduction​

This document describes and specifies Internet Identity from various angles and at various levels of abstraction, namely:

  • High level goals, requirements and use cases

  • Overview of the security and identity machinery, including the interplay of identities, keys, and delegations

  • Interface as used by client applications frontends, i.e., our client authentication protocol

  • The interface of the Internet Identity Service backend, i.e., describing its contract at the Candid layer, as used by its frontend

  • Important implementation notes about the Internet Identity Service backend

  • Internal implementation notes about the Internet Identity Service frontend

The Internet Identity Service consists of

  • its backend, a canister on the IC. More precisely, a canister on a dedicated subnet with a well-known canister id, and

  • its frontend, a web application served by the backend canister.

Similarly, the client applications consist of a frontend (served by a canister) and (typically) one or more backend canisters. Only the frontend interacts with the Internet Identity Service directly (via the client authentication protocol described below).

Goals, requirements and use cases​

The Internet Identity service allows users to

  • maintain identities on the Internet Computer

  • log in with these identities using one out of a set of security devices

  • manage their set of security devices

Some functional requirements are

  • users have separate identities (or "pseudonyms") per client application (more precisely, per client application frontend "hostname", though see Alternative Frontend Origins for caveat about .raw domains)

  • these identities are stable, i.e., do not depend on a user's security devices

  • the client frontends interact with any canister on the Internet Computer under the user's identity with that frontend

  • users do not need ever to remember secret information (but possibly per-user non-secret information)

  • a security device does not need to be manually touched upon every interaction with a client application; a login is valid for a certain amount of time per identity

Some security requirements are

  • The separate identities of a single user cannot be related merely based on their public key or principal ids, to impede user tracking.

  • The security of the identities does not depend on the privacy of data stored on canisters, or transmitted to and from canisters. In particular, the delegations handed out by the backend canister must not be sensitive information.

  • (many more, of course; apply common sense)

Some noteworthy security assumptions are:

  • The delivery of frontend applications is secure. In particular, a user accessing the Internet Identity Service Frontend through a TLS-secured HTTP connection cannot be tricked into running another web application.

Just for background: At launch this meant we relied on the trustworthiness of the boundary nodes as well as the replica the boundary nodes happens to fetch the assets from. After launch, certification of our HTTP Gateway protocol and trustworthy client-side code (browser extensions, proxies, etc.) have improved this situation.

  • The security devices only allow the use of their keys from the same web application that created the key (in our case, the Internet Identity Service Frontend).

  • The user's browser is trustworthy, postMessage communication between different origins is authentic.

  • For user privacy, we also assume the Internet Identity Service backend can keep a secret (but since data is replicated, we do not rely on this assumption for other security properties).

Identity design and data model​

The Internet Computer serves this frontend under hostnames https://identity.ic0.app (official) and https://identity.internetcomputer.org (experimental).

The canister maintains a salt (in the following the salt), a 32 byte long blob that is obtained via the Internet Computer's source of secure randomness.

Due to replication of data in canisters, the salt should not be considered secret against a determined attacker. However, the canister will not reveal the salt directly and to the extent it is unknown to an attacker it helps maintain privacy of user identities.

A user account is identified by a unique Identity Anchor, a smallish natural number chosen by the canister.

A client application frontend is identified by its hostname (e.g., abcde-efg.ic0.app, nice-name.ic0.app, non-ic-application.com). Frontend application can be served by canisters or by websites that are not hosted on the Internet Computer.

A user has a separate user identity for each client application frontend (i.e., per hostname). This identity is a self-authenticating id of the DER encoded canister signature public key which has the form

user_id = SHA-224(DER encoded public key) · 0x02` (29 bytes)

and the BIT STRING field of the DER encoded public key has the form

bit_string = |ii_canister_id| · ii_canister_id · seed

where the seed is derived as follows

seed = H(|salt| · salt · |user_number| · user_number · |frontend_host| · frontend_host)

where H is SHA-256, · is concatenation, |…| is a single byte representing the length of … in bytes, user_number is the ASCII-encoding of the Identity Anchor as a decimal number, and frontend_host is the ASCII-encoding of the client application frontend's hostname (at most 255 bytes).

A frontend_host of the form <canister id>.icp0.io will be rewritten to <canister id>.ic0.app before being used in the seed. This ensures transparent pseudonym transfer between apps hosted on ic0.app and icp0.io domains.

The Internet Identity Service Backend stores the following data in user accounts, indexed by the respective Identity Anchor:

  • a set of device information, consisting of

    • the device's public key (DER-encoded)

    • a device alias, chosen by the user to recognize the device

    • an optional credential id, which is necessary for WebAuthn authentication

When a client application frontend wants to authenticate as a user, it uses a session key (e.g., Ed25519 or ECDSA), and by way of the authentication flow (details below) obtains a delegation chain that allows the session key to sign for the user's main identity.

The delegation chain consists of one delegation, called the client delegation. It delegates from the user identity (for the given client application frontend) to the session key. This delegation is created by the Internet Identity Service Canister, and signed using a canister signature. This delegation is unscoped (valid for all canisters) and has a maximum lifetime of 30 days, with a default of 30 minutes.

The Internet Identity Service Frontend also manages an identity frontend delegation, delegating from the security device's public key to a session key managed by this frontend, so that it can interact with the backend without having to invoke the security device for each signature.

Client authentication protocol​

This section describes the Internet Identity Service from the point of view of a client application frontend.

  1. The client application frontend creates a session key pair (e.g., Ed25519).

  2. It installs a message event handler on its own window.

  3. It loads the url https://identity.ic0.app/#authorize in a separate tab. Let identityWindow be the Window object returned from this.

  4. In the identityWindow, the user logs in, and the identityWindow invokes

    window.opener.postMessage(msg, "*")

    where msg is

    interface InternetIdentityReady {
      kind: "authorize-ready"
    }

  5. The client application, after receiving the InternetIdentityReady, invokes

    identityWindow.postMessage(msg, "https://identity.ic0.app")

    where msg is a value of type

    interface InternetIdentityAuthRequest {
      kind: "authorize-client";
      sessionPublicKey: Uint8Array;
      maxTimeToLive?: bigint;
      allowPinAuthentication?: boolean;
      derivationOrigin?: string;
      autoSelectionPrincipal?: string
    }

    where

    • the sessionPublicKey contains the public key of the session key pair.

    • the maxTimeToLive, if present, indicates the desired time span (in nanoseconds) until the requested delegation should expire. The Identity Provider frontend is free to set an earlier expiry time, but should not create a one larger.

    • the allowPinAuthentication (EXPERIMENTAL), if present, indicates whether or not the Identity Provider should allow the user to authenticate and/or register using a temporary key/PIN identity. Authenticating dapps may want to prevent users from using Temporary keys/PIN identities because Temporary keys/PIN identities are less secure than Passkeys (webauthn credentials) and because Temporary keys/PIN identities generally only live in a browser database (which may get cleared by the browser/OS).

    • the derivationOrigin, if present, indicates an origin that should be used for principal derivation instead of the client origin. Internet Identity will validate the derivationOrigin by checking that it lists the client application origin in the /.well-known/ii-alternative-origins file (see Alternative Frontend Origins).

    • the autoSelectionPrincipal, if present, indicates the textual representation of this dapp's principal for which the delegation is requested. If it is known to Internet Identity, it will skip the identity selection and immediately prompt for authentication. This feature can be used to streamline re-authentication after a session expiry.

  1. Now the client application window expects a message back, with data event.

  2. If event.origin is not either "https://identity.ic0.app" or "https://identity.internetcomputer.org" (depending on which endpoint you are using), ignore this message.

  3. The event.data value is a JS object with the following type:

    interface InternetIdentityAuthResponse {
      kind: "authorize-client-success";
      delegations: [{
        delegation: {
          pubkey: Uint8Array;
          expiration: bigint;
          targets?: Principal[];
        };
        signature: Uint8Array;
      }];
      userPublicKey: Uint8Array;
      authnMethod: "passkey";
    }

    where the userPublicKey is the user's Identity on the given frontend and delegations corresponds to the CBOR-encoded delegation chain as used for authentication on the IC and authnMethod is the method used by the user to authenticate (passkey for webauthn, pin for temporary key/PIN identity, and recovery for recovery phrase or recovery device).

  4. It could also receive a failure message of the following type

    interface InternetIdentityAuthResponse {
      kind: "authorize-client-failure";
      text: string;
    }

    The client application frontend needs to be able to detect when any of the delegations in the chain has expired, and re-authorize the user in that case.

The @dfinity/auth-client NPM package provides helpful functionality here.

The client application frontend should support delegation chains of length more than one, and delegations with targets, even if the present version of this spec does not use them, to be compatible with possible future versions.

The Internet Identity frontend will use event.origin as the "Frontend URL" to base the user identity on. This includes protocol, full hostname and port. This means

  • Changing protocol, hostname (including subdomains) or port will invalidate all user identities.

  • The frontend application must never allow any untrusted JavaScript code to be executed, on any page on that hostname. Be careful when implementing a JavaScript playground on the Internet Computer.

Alternative Frontend Origins​

To allow flexibility regarding the canister frontend URL, the client may choose to provide another URL as the derivationOrigin (see Client authentication protocol). This means that Internet Identity will issue the same principals to the frontend (which uses a different origin) as it would if it were using the derivationOrigin directly. This feature works for canisterId based URLs and ICP custom domains (backed by canisters) as derivationOrigin.

This feature is intended to allow more flexibility with respect to the origins of a single service. Do not use this feature to allow third party services to use the same principals. Only add origins you fully control to /.well-known/ii-alternative-origins and never set origins you do not control as derivationOrigin!

https://<canister_id>.ic0.app and https://<canister_id>.raw.ic0.app do not issue the same principals by default . However, this feature can also be used to map https://<canister_id>.raw.ic0.app to https://<canister_id>.ic0.app principals or vice versa.

In order for Internet Identity to accept the derivationOrigin the origin of the client application must be listed in the JSON object served on the URL https://<canister_id>.icp0.io/.well-known/ii-alternative-origins (i.e. the file must be hosted by an ICP canister that must implement the http_request query call as specified here).

JSON Schema​

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "II Alternative Origins Principal Derivation Origins",
  "description": "An object containing the alternative frontend origins of the given canister, which are allowed to use the URL this document is hosted on for principal derivation.",
  "type": "object",
  "properties": {
    "alternativeOrigins": {
      "description": "List of allowed alternative frontend origins",
      "type": "array",
      "items": {
        "type": "string"
      },
      "minItems": 0,
      "maxItems": 10,
      "uniqueItems": true
    }
  },
  "required": [ "alternativeOrigins" ]
}

Example​

{
  "alternativeOrigins": [
    "https://alternative-1.com",
    "https://www.nice-frontend-name.org"
  ]
}

The path /.well-known/ii-alternative-origins will always be requested using the non-raw https://<canister_id>.ic0.app domain (even if the derivationOrigin uses a .raw) and must be delivered as a certified asset. Requests to /.well-known/ii-alternative-origins must be answered with a 200 HTTP status code. More specifically Internet Identity will not follow redirects and fail with an error instead. These measures are required in order to prevent malicious boundary nodes or replicas from tampering with ii-alternative-origins.

To prevent misuse of this feature, the number of alternative origins must not be greater than 10.

In order to allow Internet Identity to read the path /.well-known/ii-alternative-origins, the CORS response header Access-Control-Allow-Origin must be set and allow the Internet Identity origin https://identity.ic0.app.

The Internet Identity Service Backend interface​

This section describes the interface that the backend canister provides.

This interface is currently only used by its own frontend. This tight coupling means that this interface may change, even in incompatible ways. We therefore do not have to apply Candid best practices for backward-compatibility (such as using records for arguments and results).

The summary is given by the Candid interface:

type UserNumber = nat64;
type PublicKey = blob;
type CredentialId = blob;
type DeviceKey = PublicKey;
type UserKey = PublicKey;
type SessionKey = PublicKey;
type FrontendHostname = text;
type Timestamp = nat64;

type HeaderField = record {
    text;
    text;
};

type HttpRequest = record {
    method: text;
    url: text;
    headers: vec HeaderField;
    body: blob;
    certificate_version: opt nat16;
};

type HttpResponse = record {
    status_code: nat16;
    headers: vec HeaderField;
    body: blob;
    upgrade : opt bool;
    streaming_strategy: opt StreamingStrategy;
};

type StreamingCallbackHttpResponse = record {
    body: blob;
    token: opt Token;
};

type Token = record {};

type StreamingStrategy = variant {
    Callback: record {
        callback: func (Token) -> (StreamingCallbackHttpResponse) query;
        token: Token;
    };
};

type Purpose = variant {
    recovery;
    authentication;
};

type KeyType = variant {
    unknown;
    platform;
    cross_platform;
    seed_phrase;
    browser_storage_key;
};

// This describes whether a device is "protected" or not.
// When protected, a device can only be updated or removed if the
// user is authenticated with that very device.
type DeviceProtection = variant {
    protected;
    unprotected;
};

type Challenge = record {
    png_base64: text;
    challenge_key: ChallengeKey;
};

type DeviceData = record {
    pubkey : DeviceKey;
    alias : text;
    credential_id : opt CredentialId;
    purpose: Purpose;
    key_type: KeyType;
    protection: DeviceProtection;
    origin: opt text;
    // Metadata map for additional device information.
    //
    // Note: some fields above will be moved to the metadata map in the future.
    // All field names of `DeviceData` (such as 'alias', 'origin, etc.) are
    // reserved and cannot be written.
    // In addition, the keys "usage" and "authenticator_attachment" are reserved as well.
    metadata: opt MetadataMap;
};

// The same as `DeviceData` but with the `last_usage` field.
// This field cannot be written, hence the separate type.
type DeviceWithUsage = record {
    pubkey : DeviceKey;
    alias : text;
    credential_id : opt CredentialId;
    purpose: Purpose;
    key_type: KeyType;
    protection: DeviceProtection;
    origin: opt text;
    last_usage: opt Timestamp;
    metadata: opt MetadataMap;
};

// Map with some variants for the value type.
// Note, due to the Candid mapping this must be a tuple type thus we cannot name the fields `key` and `value`.
type MetadataMap = vec record {
    text;
    variant { map : MetadataMap; string : text; bytes : vec nat8 };
};

type RegisterResponse = variant {
    // A new user was successfully registered.
    registered: record {
        user_number: UserNumber;
    };
    // No more registrations are possible in this instance of the II service canister.
    canister_full;
    // The challenge was not successful.
    bad_challenge;
};

type AddTentativeDeviceResponse = variant {
    // The device was tentatively added.
    added_tentatively: record {
        verification_code: text;
        // Expiration date, in nanos since the epoch
        device_registration_timeout: Timestamp;
    };
    // Device registration mode is off, either due to timeout or because it was never enabled.
    device_registration_mode_off;
    // There is another device already added tentatively
    another_device_tentatively_added;
};

type VerifyTentativeDeviceResponse = variant {
    // The device was successfully verified.
    verified;
    // Wrong verification code entered. Retry with correct code.
    wrong_code: record {
        retries_left: nat8
    };
    // Device registration mode is off, either due to timeout or because it was never enabled.
    device_registration_mode_off;
    // There is no tentative device to be verified.
    no_device_to_verify;
};

type Delegation = record {
    pubkey: PublicKey;
    expiration: Timestamp;
    targets: opt vec principal;
};

type SignedDelegation = record {
    delegation: Delegation;
    signature: blob;
};

type GetDelegationResponse = variant {
    // The signed delegation was successfully retrieved.
    signed_delegation: SignedDelegation;

    // The signature is not ready. Maybe retry by calling `prepare_delegation`
    no_such_delegation
};

type InternetIdentityStats = record {
    users_registered: nat64;
    storage_layout_version: nat8;
    assigned_user_number_range: record {
        nat64;
        nat64;
    };
    archive_info: ArchiveInfo;
    canister_creation_cycles_cost: nat64;
    // Map from event aggregation to a sorted list of top 100 sub-keys to their weights.
    // Example: {"prepare_delegation_count 24h ic0.app": [{"https://dapp.com", 100}, {"https://dapp2.com", 50}]}
    event_aggregations: vec record {text; vec record {text; nat64}};
};

// Configuration parameters related to the archive.
type ArchiveConfig = record {
    // The allowed module hash of the archive canister.
    // Changing this parameter does _not_ deploy the archive, but enable archive deployments with the
    // corresponding wasm module.
    module_hash : blob;
    // Buffered archive entries limit. If reached, II will stop accepting new anchor operations
    // until the buffered operations are acknowledged by the archive.
    entries_buffer_limit: nat64;
    // The maximum number of entries to be transferred to the archive per call.
    entries_fetch_limit: nat16;
    // Polling interval to fetch new entries from II (in nanoseconds).
    // Changes to this parameter will only take effect after an archive deployment.
    polling_interval_ns: nat64;
};

// Information about the archive.
type ArchiveInfo = record {
    // Canister id of the archive or empty if no archive has been deployed yet.
    archive_canister : opt principal;
    // Configuration parameters related to the II archive.
    archive_config: opt ArchiveConfig;
};

// Rate limit configuration.
// Currently only used for `register`.
type RateLimitConfig = record {
    // Time it takes (in ns) for a rate limiting token to be replenished.
    time_per_token_ns : nat64;
    // How many tokens are at most generated (to accommodate peaks).
    max_tokens: nat64;
};

// Init arguments of II which can be supplied on install and upgrade.
// Setting a value to null keeps the previous value.
type InternetIdentityInit = record {
    // Set lowest and highest anchor
    assigned_user_number_range : opt record {
        nat64;
        nat64;
    };
    // Configuration parameters related to the II archive.
    // Note: some parameters changes (like the polling interval) will only take effect after an archive deployment.
    // See ArchiveConfig for details.
    archive_config: opt ArchiveConfig;
    // Set the amounts of cycles sent with the create canister message.
    // This is configurable because in the staging environment cycles are required.
    // The canister creation cost on mainnet is currently 100'000'000'000 cycles. If this value is higher thant the
    // canister creation cost, the newly created canister will keep extra cycles.
    canister_creation_cycles_cost : opt nat64;
    // Rate limit for the `register` call.
    register_rate_limit : opt RateLimitConfig;
    // Maximum number of inflight captchas.
    // Default: 500
    max_inflight_captchas: opt nat64;
};

type ChallengeKey = text;

type ChallengeResult = record {
    key : ChallengeKey;
    chars : text;
};
type CaptchaResult = ChallengeResult;

// Extra information about registration status for new devices
type DeviceRegistrationInfo = record {
    // If present, the user has tentatively added a new device. This
    // new device needs to be verified (see relevant endpoint) before
    // 'expiration'.
    tentative_device : opt DeviceData;
    // The timestamp at which the anchor will turn off registration mode
    // (and the tentative device will be forgotten, if any, and if not verified)
    expiration: Timestamp;
};

// Information about the anchor
type IdentityAnchorInfo = record {
    // All devices that can authenticate to this anchor
    devices : vec DeviceWithUsage;
    // Device registration status used when adding devices, see DeviceRegistrationInfo
    device_registration: opt DeviceRegistrationInfo;
};

type AnchorCredentials = record {
    credentials : vec WebAuthnCredential;
    recovery_credentials : vec WebAuthnCredential;
    recovery_phrases: vec PublicKey;
};

type WebAuthnCredential = record {
    credential_id : CredentialId;
    pubkey: PublicKey;
};

type DeployArchiveResult = variant {
    // The archive was deployed successfully and the supplied wasm module has been installed. The principal of the archive
    // canister is returned.
    success: principal;
    // Initial archive creation is already in progress.
    creation_in_progress;
    // Archive deployment failed. An error description is returned.
    failed: text;
};

type BufferedArchiveEntry = record {
    anchor_number: UserNumber;
    timestamp: Timestamp;
    sequence_number: nat64;
    entry: blob;
};

// API V2 specific types
// WARNING: These type are experimental and may change in the future.

type IdentityNumber = nat64;

// Map with some variants for the value type.
// Note, due to the Candid mapping this must be a tuple type thus we cannot name the fields `key` and `value`.
type MetadataMapV2 = vec record {
    text;
    variant { Map : MetadataMapV2; String : text; Bytes : vec nat8 };
};

// Authentication method using WebAuthn signatures
// See https://www.w3.org/TR/webauthn-2/
// This is a separate type because WebAuthn requires to also store
// the credential id (in addition to the public key).
type WebAuthn = record {
    credential_id: CredentialId;
    pubkey: PublicKey;
};

// Authentication method using generic signatures
// See https://internetcomputer.org/docs/current/references/ic-interface-spec/#signatures for
// supported signature schemes.
type PublicKeyAuthn = record {
    pubkey: PublicKey;
};

// The authentication methods currently supported by II.
type AuthnMethod = variant {
    WebAuthn: WebAuthn;
    PubKey: PublicKeyAuthn;
};

// This describes whether an authentication method is "protected" or not.
// When protected, a authentication method can only be updated or removed if the
// user is authenticated with that very authentication method.
type AuthnMethodProtection = variant {
    Protected;
    Unprotected;
};

type AuthnMethodPurpose = variant {
    Recovery;
    Authentication;
};

type AuthnMethodSecuritySettings = record {
    protection: AuthnMethodProtection;
    purpose: AuthnMethodPurpose;
};

type AuthnMethodData = record {
    authn_method: AuthnMethod;
    security_settings: AuthnMethodSecuritySettings;
    // contains the following fields of the DeviceWithUsage type:
    // - alias
    // - origin
    // - authenticator_attachment: data taken from key_type and reduced to "platform", "cross_platform" or absent on migration
    // - usage: data taken from key_type and reduced to "recovery_phrase", "browser_storage_key" or absent on migration
    // Note: for compatibility reasons with the v1 API, the entries above (if present)
    // must be of the `String` variant. This restriction may be lifted in the future.
    metadata: MetadataMapV2;
    last_authentication: opt Timestamp;
};

// Extra information about registration status for new authentication methods
type AuthnMethodRegistrationInfo = record {
    // If present, the user has registered a new authentication method. This
    // new authentication needs to be verified before 'expiration' in order to
    // be added to the identity.
    authn_method : opt AuthnMethodData;
    // The timestamp at which the identity will turn off registration mode
    // (and the authentication method will be forgotten, if any, and if not verified)
    expiration: Timestamp;
};

type AuthnMethodConfirmationCode = record {
    confirmation_code: text;
    expiration: Timestamp;
};

type AuthnMethodRegisterError = variant {
    // Authentication method registration mode is off, either due to timeout or because it was never enabled.
    RegistrationModeOff;
    // There is another authentication method already registered that needs to be confirmed first.
    RegistrationAlreadyInProgress;
    // The metadata of the provided authentication method contains invalid entries.
    InvalidMetadata: text;
};

type AuthnMethodConfirmationError = variant {
    // Wrong confirmation code entered. Retry with correct code.
    WrongCode: record {
        retries_left: nat8
    };
    // Authentication method registration mode is off, either due to timeout or because it was never enabled.
    RegistrationModeOff;
    // There is no registered authentication method to be confirmed.
    NoAuthnMethodToConfirm;
};

type IdentityAuthnInfo = record {
    authn_methods: vec AuthnMethod;
    recovery_authn_methods: vec AuthnMethod;
};

type IdentityInfo = record {
    authn_methods: vec AuthnMethodData;
    authn_method_registration: opt AuthnMethodRegistrationInfo;
    // Authentication method independent metadata
    metadata: MetadataMapV2;
};

type IdentityInfoError = variant {
    /// The principal is not authorized to call this method with the given arguments.
    Unauthorized: principal;
    /// Internal canister error. See the error message for details.
    InternalCanisterError: text;
};



type IdentityRegisterError = variant {
    // No more registrations are possible in this instance of the II service canister.
    CanisterFull;
    // The captcha check was not successful.
    BadCaptcha;
    // The metadata of the provided authentication method contains invalid entries.
    InvalidMetadata: text;
};

type AuthnMethodAddError = variant {
    InvalidMetadata: text;
};

type AuthnMethodReplaceError = variant {
    InvalidMetadata: text;
    // No authentication method found with the given public key.
    AuthnMethodNotFound;
};

type AuthnMethodMetadataReplaceError = variant {
    InvalidMetadata: text;
    /// No authentication method found with the given public key.
    AuthnMethodNotFound;
};

type AuthnMethodSecuritySettingsReplaceError = variant {
    /// No authentication method found with the given public key.
    AuthnMethodNotFound;
};

type IdentityMetadataReplaceError = variant {
    /// The principal is not authorized to call this method with the given arguments.
    Unauthorized: principal;
    /// The identity including the new metadata exceeds the maximum allowed size.
    StorageSpaceExceeded: record {space_available: nat64; space_required: nat64};
    /// Internal canister error. See the error message for details.
    InternalCanisterError: text;
};

type PrepareIdAliasRequest = record {
    /// Origin of the issuer in the attribute sharing flow.
    issuer : FrontendHostname;
    /// Origin of the relying party in the attribute sharing flow.
    relying_party : FrontendHostname;
    /// Identity for which the IdAlias should be generated.
    identity_number : IdentityNumber;
};

type PrepareIdAliasError = variant {
    /// The principal is not authorized to call this method with the given arguments.
    Unauthorized: principal;
    /// Internal canister error. See the error message for details.
    InternalCanisterError: text;
};

/// The prepared id alias contains two (still unsigned) credentials in JWT format,
/// certifying the id alias for the issuer resp. the relying party.
type PreparedIdAlias = record {
    rp_id_alias_jwt : text;
    issuer_id_alias_jwt : text;
    canister_sig_pk_der : PublicKey;
};

/// The request to retrieve the actual signed id alias credentials.
/// The field values should be equal to the values of corresponding
/// fields from the preceding `PrepareIdAliasRequest` and `PrepareIdAliasResponse`.
type GetIdAliasRequest = record {
    rp_id_alias_jwt : text;
    issuer : FrontendHostname;
    issuer_id_alias_jwt : text;
    relying_party : FrontendHostname;
    identity_number : IdentityNumber;
};

type GetIdAliasError = variant {
    /// The principal is not authorized to call this method with the given arguments.
    Unauthorized: principal;
    /// The credential(s) are not available: may be expired or not prepared yet (call prepare_id_alias to prepare).
    NoSuchCredentials : text;
    /// Internal canister error. See the error message for details.
    InternalCanisterError: text;
};

/// The signed id alias credentials for each involved party.
type IdAliasCredentials = record {
    rp_id_alias_credential : SignedIdAlias;
    issuer_id_alias_credential : SignedIdAlias;
};

type SignedIdAlias = record {
    credential_jws : text;
    id_alias : principal;
    id_dapp : principal;
};

service : (opt InternetIdentityInit) -> {
    init_salt: () -> ();
    create_challenge : () -> (Challenge);
    register : (DeviceData, ChallengeResult, opt principal) -> (RegisterResponse);
    add : (UserNumber, DeviceData) -> ();
    update : (UserNumber, DeviceKey, DeviceData) -> ();
    // Atomically replace device matching the device key with the new device data
    replace : (UserNumber, DeviceKey, DeviceData) -> ();
    remove : (UserNumber, DeviceKey) -> ();
    // Returns all devices of the user (authentication and recovery) but no information about device registrations.
    // Note: Clears out the 'alias' fields on the devices. Use 'get_anchor_info' to obtain the full information.
    // Deprecated: Use 'get_anchor_credentials' instead.
    lookup : (UserNumber) -> (vec DeviceData) query;
    get_anchor_credentials : (UserNumber) -> (AnchorCredentials) query;
    get_anchor_info : (UserNumber) -> (IdentityAnchorInfo);
    get_principal : (UserNumber, FrontendHostname) -> (principal) query;
    stats : () -> (InternetIdentityStats) query;

    enter_device_registration_mode : (UserNumber) -> (Timestamp);
    exit_device_registration_mode : (UserNumber) -> ();
    add_tentative_device : (UserNumber, DeviceData) -> (AddTentativeDeviceResponse);
    verify_tentative_device : (UserNumber, verification_code: text) -> (VerifyTentativeDeviceResponse);

    prepare_delegation : (UserNumber, FrontendHostname, SessionKey, maxTimeToLive : opt nat64) -> (UserKey, Timestamp);
    get_delegation: (UserNumber, FrontendHostname, SessionKey, Timestamp) -> (GetDelegationResponse) query;

    http_request: (request: HttpRequest) -> (HttpResponse) query;
    http_request_update: (request: HttpRequest) -> (HttpResponse);

    deploy_archive: (wasm: blob) -> (DeployArchiveResult);
    // Returns a batch of entries _sorted by sequence number_ to be archived.
    // This is an update call because the archive information _must_ be certified.
    // Only callable by this IIs archive canister.
    fetch_entries: () -> (vec BufferedArchiveEntry);
    acknowledge_entries: (sequence_number: nat64) -> ();

    // V2 API
    // WARNING: The following methods are experimental and may change in the future.

    // Creates a new captcha. The solution needs to be submitted using the
    // `identity_register` call.
    captcha_create: () -> (variant {Ok: Challenge; Err;});

    // Registers a new identity with the given authn_method.
    // A valid captcha solution to a previously generated captcha (using create_captcha) must be provided.
    // The sender needs to match the supplied authn_method.
    identity_register: (AuthnMethodData, CaptchaResult, opt principal) -> (variant {Ok: IdentityNumber; Err: IdentityRegisterError;});

    // Returns information about the authentication methods of the identity with the given number.
    // Only returns the minimal information required for authentication without exposing any metadata such as aliases.
    identity_authn_info: (IdentityNumber) -> (variant {Ok: IdentityAuthnInfo; Err;}) query;

    // Returns information about the identity with the given number.
    // Requires authentication.
    identity_info: (IdentityNumber) -> (variant {Ok: IdentityInfo; Err: IdentityInfoError;});

    // Replaces the authentication method independent metadata map.
    // The existing metadata map will be overwritten.
    // Requires authentication.
    identity_metadata_replace: (IdentityNumber, MetadataMapV2) -> (variant {Ok; Err: IdentityMetadataReplaceError;});

    // Adds a new authentication method to the identity.
    // Requires authentication.
    authn_method_add: (IdentityNumber, AuthnMethodData) -> (variant {Ok; Err: AuthnMethodAddError;});

    // Atomically replaces the authentication method matching the supplied public key with the new authentication method
    // provided.
    // Requires authentication.
    authn_method_replace: (IdentityNumber, PublicKey, AuthnMethodData) -> (variant {Ok; Err: AuthnMethodReplaceError;});

    // Replaces the authentication method metadata map.
    // The existing metadata map will be overwritten.
    // Requires authentication.
    authn_method_metadata_replace: (IdentityNumber, PublicKey, MetadataMapV2) -> (variant {Ok; Err: AuthnMethodMetadataReplaceError;});

    // Replaces the authentication method security settings.
    // The existing security settings will be overwritten.
    // Requires authentication.
    authn_method_security_settings_replace: (IdentityNumber, PublicKey, AuthnMethodSecuritySettings) -> (variant {Ok; Err: AuthnMethodSecuritySettingsReplaceError;});

    // Removes the authentication method associated with the public key from the identity.
    // Requires authentication.
    authn_method_remove: (IdentityNumber, PublicKey) -> (variant {Ok; Err;});

    // Enters the authentication method registration mode for the identity.
    // In this mode, a new authentication method can be registered, which then needs to be
    // confirmed before it can be used for authentication on this identity.
    // The registration mode is automatically exited after the returned expiration timestamp.
    // Requires authentication.
    authn_method_registration_mode_enter : (IdentityNumber) -> (variant {Ok: record { expiration: Timestamp; }; Err;});

    // Exits the authentication method registration mode for the identity.
    // Requires authentication.
    authn_method_registration_mode_exit : (IdentityNumber) -> (variant {Ok; Err;});

    // Registers a new authentication method to the identity.
    // This authentication method needs to be confirmed before it can be used for authentication on this identity.
    authn_method_register: (IdentityNumber, AuthnMethodData) -> (variant {Ok: AuthnMethodConfirmationCode; Err: AuthnMethodRegisterError;});

    // Confirms a previously registered authentication method.
    // On successful confirmation, the authentication method is permanently added to the identity and can
    // subsequently be used for authentication for that identity.
    // Requires authentication.
    authn_method_confirm: (IdentityNumber, confirmation_code: text) -> (variant {Ok; Err: AuthnMethodConfirmationError;});

    // Attribute Sharing MVP API
    // The methods below are used to generate ID-alias credentials during attribute sharing flow.
    prepare_id_alias : (PrepareIdAliasRequest) -> (variant {Ok: PreparedIdAlias; Err: PrepareIdAliasError;});
    get_id_alias : (GetIdAliasRequest) -> (variant {Ok: IdAliasCredentials; Err: GetIdAliasError;}) query;
}

The init_salt method is mostly internal, see Salt.

The register and create_challenge methods​

The register method is used to create a new user. The Internet Identity Service backend creates a fresh Identity Anchor, creates the account record, and adds the given device as the first device.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from the given DeviceKey.

In order to protect the Internet Computer from too many "free" update calls, and to protect the Internet Identity Service from too many user registrations, this call is protected using a CAPTCHA challenge. The register call can only succeed if the ChallengeResult contains a key for a challenge that was created with create_challenge (see below) in the last 5 minutes and if the chars match the characters that the Internet Identity Service has stored internally for that key.

The add method​

The add method appends a new device to the given user's record.

The Internet Identity Service backend rejects the call if the user already has a device on record with the given public key.

This may also fail (with a reject) if the user is registering too many devices.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The remove method​

The remove method removes a device, identified by its public key, from the list of devices a user has.

It is allowed to remove the key that is used to sign this request. This can be useful for a panic button functionality.

It is allowed to remove the last key, to completely disable a user. The canister may forget that user completely then, assuming the Identity Anchor generation algorithm prevents new users from getting the same Identity Anchor.

It is the responsibility of the frontend UI to protect the user from doing these things accidentally.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

If the device has the protected flag, then the request must be sent to the canister with caller that is the self-authenticating id derived from the public key of that particular device.

The enter_device_registration_mode method​

Enables device registration mode for the given identity anchor. When device registration mode is active, new devices can be added using add_tentative_device and verify_tentative_device. Device registration mode stays active for at most 15 minutes or until the flow is either completed or aborted.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The exit_device_registration_mode method​

Exits device registration mode immediately. Any non verified tentative devices are discarded.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The add_tentative_device method​

Tentatively adds a new device to the supplied identity anchor and returns a verification code. This code has to be used with the verify_tentative_device method to verify this device. If the flow is aborted or not completed within 15 minutes, the tentative device is discarded.

Tentatively added devices cannot be used to login into the management view or authorize authentications for other dApps.

Authorization: Anyone can call this

The verify_tentative_device method​

For an anchor in device registration mode: if called with a valid verification code, adds the tentative device as a regular device to the anchor and exits registration mode. The registration flow is aborted if this method is called five times with invalid verification codes.

Returns an error if called for a device not in registration mode.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The lookup query method​

Fetches all device data associated with a user.

Authorization: Anyone can call this

The get_anchor_info method​

Fetches all data associated with an anchor including registration mode and tentatively registered devices.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The get_principal query method​

Fetches the principal for a given user and front end.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The prepare_delegation method​

The prepare_delegation method causes the Internet Identity Service backend to prepare a delegation from the user identity associated with the given Identity Anchor and Client Application Frontend Hostname to the given session key.

This method returns the user's identity that's associated with the given Client Application Frontend Hostname. By returning this here, and not in the less secure get_delegation query, we prevent attacks that trick the user into using a wrong identity.

The expiration timestamp is determined by the backend, but no more than maxTimeToLive (if present) nanoseconds in the future.

The method returns the expiration timestamp of the delegation. This is returned purely so that the client can feed it back to the backend in get_delegation.

The actual delegation can be fetched using get_delegation immediately afterwards.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The get_delegation query method​

For a certain amount of time after a call to prepare_delegation, a query call to get_delegation with the same arguments, plus the timestamp returned from prepare_delegation, actually fetches the delegation.

Together with the UserKey returned by prepare_delegation, the result of this method is used by the Frontend to pass to the client application as per the client authentication protocol.

Authorization: This request must be sent to the canister with caller that is the self-authenticating id derived from any of the public keys of devices associated with the user before this call.

The Internet Identity Service backend internals​

This section, which is to be expanded, describes interesting design choices about the internals of the Internet Identity Service Canister. In particular

Salt​

The salt used to blind the hashes that form the seed of the Canister Signature "public keys" is obtained via a call to aaaaa-aa.raw_rand(). The resulting 32 byte sequence is used as-is.

Since this cannot be done during canister_init (no calls from canister init), the randomness is fetched by someone triggering the init_salt() method explicitly, or just any other update call. More concretely:

  • Anyone can invoke init_salt()

  • init_salt() traps if salt != EMPTY_SALT

  • Else, init_salt() calls aaaaa-aa.raw_rand(). When that comes back successfully, and still salt == EMPTY_SALT, it sets the salt. Else, it traps (so that even if it is run multiple times concurrently, only the first to write the salt has an effect).

  • all other update methods, at the beginning, if salt == EMPTY_SALT, they await self.init_salt(), ignoring the result (even if it is an error). Then they check if we still have salt == EMPTY_SALT and trap if that is the case.

Why we do not use canister_inspect_message​

The system allows canisters to inspect ingress messages before they are actually ingressed, and decide if they want to pay for them (see the interface spec). Because the Internet Identity canisters run on a system subnet, cycles are not actually charged, but we still want to avoid wasting resources.

It seems that this implies that we should use canister_inspect_message to reject messages that would, for example, not pass authentication.

But upon closer inspection (heh), this is not actually useful.

  • One justification for this mechanism would be if we expect a high number of accidentally invalid calls. But we have no reason to expect them at the moment.

  • Another is to protect against a malicious actor. But that is only useful if the malicious actor doesn't have an equally effective attack vector anyways, and in our case they do: If they want to flood the NNS with calls, they can use calls that do authenticate (e.g. keeping removing and adding devices, or preparing delegations); these calls would pass message inspection.

On the flip side, implementing canister_inspect_message adds code, and thus a risk for bugs. In particular it increases the risk that some engineer might wrongly assume that the authentication check in canister_inspect_message is sufficient and will not do it again in the actual method, which could lead to a serious bug.

Therefore the Internet Identity Canister intentionally does not implement canister_inspect_message.

Internal data model and data structures used​

The primary data structure used by the backend is a map from Identity Anchor to the list of user devices. Device lists are stored directly in canister stable memory. The total amount of storage is limited to 2KiB bytes per user. With the stable memory size of 8GiB we can store around 4 * 10^6 user records in a single canister.

Stable memory layout​

All the integers (u64, u32, u16) are encoded in Little-Endian.

Storage ::= {
  Header
  UserRecords
}

Header ::= {
  magic : u8[3] = "IIC"
  version : u8 = 1
  number_of_user_records : u32
  user_number_range_lo : u64
  user_number_range_hi : u64
  entry_size: u16
  salt: u8[32]
  padding : u8[454]
}

UserRecords ::= UserRecord*

UserRecord ::= {
  size : u16
  candid_bytes: u8[510]
}

User record for Identity Anchor N is stored at offset sizeof(Header) + (N - user_number_range_lo) * sizeof(UserRecord). Each record consists of a 16 bit size ∈ [0..510] followed by size bytes of Candid-serialized list of devices.

type UserDeviceList = vec(record {
  pubkey : DeviceKey;
  alias : text;
  credential_id : opt CredentialId;
});

Initialization​

The Internet Identity canister is designed for sharded deployments. There can be many simultaneously installed instances of the canister code, each serving requests of a subset of users. As users are identified by their Identity Anchor, we split the range of Identity Anchors into continuous non-overlapping half-closed intervals and assign each region to one canister instance. The assigned range is passed to the canister as an init argument, encoded in Candid:

type InternetIdentityInit = record {
  // Half-closed interval of Identity Anchors assigned to this canister, [ left_bound, right_bound )
  assigned_user_number_range: record { nat64; nat64; };
};

Approach to upgrades​

We don't need any logic recovery logic in pre/post-upgrade hooks because we place all user data to stable memory in a way that can be accessed directly. The signature map is simply dropped on upgrade, so users will have to re-request their delegations.

The Internet Identity Service frontend​

The Internet Identity Service frontend is the user-visible part of the Internet Identity Service, and where it all comes together. It communicates with

  • the user

  • its backend using the Candid interface described above

  • the security devices, using the Web Authentication API

  • its past and future self, via the browser storage

  • client application frontends, via the OAUTH protocol

Storage used​

The frontend only stores a single piece of local storage, namely the current Identity Anchor, if known under the key user_number.

Flows​

The following flows are not prescriptive of the UI, e.g. "the frontend asks the user for X" may also mean that on the previous shown page, there is already a field for X.

The possible login subflows are shared among entry points / and /authorized, and are thus described separately. At the end of a successful login subflow:

  • The frontend knows the user_number (also stored in local storage).

  • the frontend has a temporary session key

  • the frontend has a device_identity for the present security device

  • the frontend has a frontend_delegation from the security device to the session key

All update calls to the Internet Identity Service Backend are made under the device_identity and are signed with the session key.

The steps marked with 👆 are the steps where the user presses the security device.

Subflow: Login as returning user​

  1. The frontend notices that user_number is present in local storage.

  2. The frontend offers the choices

    • Welcome <Identity Anchor>. Do you want to log in?

    • Log in as a different user

  3. User wants to log in

  4. The frontend uses lookup to fetch the list of devices

  5. The frontend creates a session key.

  6. 👆 The frontend creates a delegation from the security device key to the session key, and signs it with the security key, using any of the devices listed in the user account. It notes which device was actually used.

    Let device_identity of type WebAuthenicationIdentity be the identity created from that, and let frontend_delegation be the signed delegation.

  7. The frontend configures the agent to use the session key for all further update calls.

  8. Login complete

Subflow: Login via initial registration​

  1. The frontend notices that no user_number is present in local storage.

  2. The frontend offers the choices

    • Create new account

    • Log into existing account with existing device

    • Log into existing account with new device

  3. The user chooses to create a new account

  4. 👆 The frontend asks the security device to create a new public key. Let device_identity of type WebAuthenicationIdentity be the identity created from that.

  5. The frontend creates a session key.

  6. 👆 The frontend creates a delegation from the security device key to the session key, and signs it with the security key. Let frontend_delegation be that signed delegation.

  7. The frontend configures the agent to use the session key for all further update calls.

  8. The frontend asks the user for a device alias.

  9. The frontend calls register(), and obtains the user_number.

  10. It stores the user_number in local storage.

  11. The frontend insistently tells the user to write down this number.

  12. The frontend asks the user to create a recovery option (see Flow: Setup Recovery)

  13. Login complete

Subflow: Login via existing device​

  1. The frontend notices that no user_number is present in local storage. (Or user said "log in as different user" in returning flow.)

  2. The frontend offers the choices

    • Create new account

    • Log into existing account with existing device

    • Log into existing account with new device

  3. The user selects "Log into existing account with existing device"

  4. The frontend asks the user for their Identity Anchor, and stores that in user_number.

  5. Continue as in "Subflow: Login as returning user"

Subflow: Login via new device​

  1. The frontend notices that no user_number is present in local storage.

  2. The frontend offers the choices

    • Create new account

    • Log into existing account with existing device

    • Log into existing account with new device

  3. The user selects "Log into existing account with new device"

  4. The frontend asks the user for their Identity Anchor.

  5. The frontend asks the user for a device alias.

  6. 👆 Frontend asks security device for a new public key and credential id.

  7. The frontend calls add_tentative_device()

  8. The frontend polls lookup() until the credential id is present or the timeout is reached.

  9. The frontend stores the user_number in local storage

  10. Login complete

(See "Flow: adding remote device" for what happens on the other device.)

Flow: Direct access to the frontend​

This flow is the boring default

  1. User browses to https://identity.ic0.app/

  2. 👆 The appropriate login subflow happens

  3. User sees their management screen. In particular

    • Their Identity Anchor

    • A button to add additional devices

    • The list of their devices, with device aliases, a symbol marking recovery devices, and a button to remove

    • A "logout" button

One could imagine additional information, such as the last time a device was used, or even a list of recent client applications that the user logged into.

Flow: adding remote device​

  1. The user accesses https://identity.ic0.app/

  2. 👆 The appropriate login subflow happens

  3. On the management page the user selects \"Add New Device\"

  4. On the flow selection screen the user selects \"Remote Device\"

    • Call enter_device_registration_mode() to start device registration flow

  5. The UI polls get_anchor_info() until a tentative device is present or the timeout is reached

    • Now the "Flow: Login via new device" happens on the remote device

  6. The user enters the verification code

    • Call verify_tentative_device() to complete the flow

Flow: Setup recovery​

  1. The user is offered two options for recovery and the option to skip

    • A security key

    • A BIP-39 seed phrase

  2. Depending on their choice a) If they choose the seed phrase it is generated and displayed to them with a copy button and an explanation of having to keep this phrase secure b) 👆 If they choose the security key they generate new credentials for the touched device

  3. The device is added to the users account with the purpose #recovery set

Flow: Use recovery​

  1. On the login page the user selects "Recover my account"

  2. The user is prompted for their Identity Anchor

  3. If no DeviceData with the purpose #recovery is found for the Identity Anchor an error is displayed

  4. The user is asked to provide the seed phrase or 👆 their recovery security key

  5. The management page is shown

Flow: authenticating client applications​

  1. The user accesses /#authorize

  2. 👆 The appropriate login subflow happens

  3. The frontend listens to a message event (as per postMessage API)

  4. The event.data should be a message as per our Client authentication protocol.

  5. If the message contains a value for derivationOrigin:

    • If the derivationOrigin value does not match the format specified in the section Client authentication protocol, the process flow is aborted with a failure message.
    • The frontend calls https://<canister_id>.ic0.app/.well-known/ii-alternative-origins to retrieve the allowed alter native origins.
    • If there is no such certified asset the flow is aborted with a failure message.
    • The frontend validates the retrieved data as per schema specified in section JSON Schema
    • If the event.origin is contained in the array value of the property alternativeOrigins the derivationOrigin will be used as the Application Frontend’s hostname.

  6. If the message does not contain a value for derivationOrigin the event.origin is used as the Application Frontend’s hostname

  7. The user is asked if they want to log into the client application, showing the client application frontend’s hostname.

  8. The frontend calls prepare_delegation() with the client application frontend hostname, client application provided session key and desired time to live.

  9. The frontend queries get_delegation() to get the delegation data

  10. It posts that data to the client application, using event.source.postMessage and the types specified in Client authentication protocol.

  11. After receiving the data the client application is expected to close the Internet Identity window / tab.

Flow: Deleting devices​

  1. The user is logged in, on the management view, and selects a device to delete.

  2. If this is the device the user is currently logged in (the current device_identity), the user is warned.

  3. If this is the last device of the user, the user is warned even more sternly.

  4. The device is removed via remove().

  5. If this was the device that the user has logged in with, log out (as per "Flow: logging out")

  6. Else, refresh the device view.

Flow: Logging out​

  1. The user is logged in, on the management view, and clicks the logout button.

  2. The user_number is removed from local storage

  3. The page is reloaded (to send the user back to the beginning of "Flow: Direct access").