biometrics/face/1.0/IBiometricsFace.hal

/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.hardware.biometrics.face@1.0;

import IBiometricsFaceClientCallback;

// TODO(b/78538290): Update comments with state machine transitions when ready.
// TODO(b/78537981): Update comments with callback interaction contract.
// TODO(b/79496983): Update comments with status returns fully enumerated.
/**
 * The HAL interface for biometric face authentication.
 */
interface IBiometricsFace {

    /**
     * Sets the current client callback.
     *
     * Registers a user function that must receive notifications from the HAL.
     * There is usually only one client (FaceService). This call must block
     * if the HAL state machine is in busy state until the HAL leaves the
     * busy state.
     *
     * All callback methods pass a deviceId to differentiate callback
     * invocations in the case where multiple sensors exist.
     *
     * @param clientCallback The client defined callback to register.
     * @return result, with its "value" parameter representing a "deviceId",
     *     which must be unique for a given sensor.
     */
    @callflow(next={"setActiveUser"})
    @entry
    setCallback(IBiometricsFaceClientCallback clientCallback)
        generates (OptionalUint64 result);

    /**
     * Sets the active user, which all subsequent HAL operations are applied to.
     *
     * HAL service implementors must ensure that operations are restricted to
     * the given user. Clients must not call any part of this interface, except
     * for setCallback(), without first having set an active user. The
     * implementation is responsible for cancelling the current operation and
     * returning to the idle state. Calling this method with the same userId
     * should have no effect on the state machine.
     *
     * @param userId A non-negative user identifier that must be unique and
     *     persistent for a given user.
     * @param storePath filesystem path to the template storage directory.
     */
    @callflow(next={"authenticate", "generateChallenge", "enumerate", "remove"})
    setActiveUser(int32_t userId, string storePath) generates (Status status);

    /**
     * Begins a secure transaction request, e.g. enrollment.
     *
     * Generates a unique and cryptographically secure random token used to
     * indicate the start of a secure transaction. generateChallenge() and
     * revokeChallenge() specify a pin/pattern/password cleared time window where
     * the secure transaction is allowed.
     *
     * generateChallenge() generates a challenge which must then be wrapped by the
     * gatekeeper after verifying a successful strong authentication attempt,
     * which generates a Hardware Authentication Token. The challenge prevents
     * spoofing and replay attacks and ensures that we only update a user’s face
     * template if the operation was preceded by some kind of strong credential
     * confirmation (e.g. device password).
     *
     * @return result, with its "value" parameter representing a "challenge": a
     *     unique and cryptographically secure random token.
     */
    @callflow(next={"enroll", "revokeChallenge", "setRequireAttention"})
    generateChallenge() generates (OptionalUint64 result);

    /**
     * Enrolls a user's face.
     *
     * Note that this interface permits implementations where multiple faces can
     * be enrolled for a single user. However, allowing multiple faces to be
     * enrolled can be a severe security vulnerability and hence, most
     * implementations must ensure that only a single face be enrolled at a
     * given time. Multi-enrollment must only be used where there is a clear
     * necessity for a shared use case, e.g. TVs or cars.
     *
     * Note that the Hardware Authentication Token must still be valid after
     * this call, and must be explicitly invalidated by a call to
     * revokeChallenge(). This allows clients to immediately reattempt
     * enrollment (for example, if a user wasn’t satisfied with their enrollment)
     * without having to go through another strong authentication flow.
     *
     * This method triggers the IBiometricsFaceClientCallback#onEnrollResult()
     * method.
     *
     * @param hat A valid Hardware Authentication Token, generated as a result
     *     of a generateChallenge() challenge being wrapped by the gatekeeper
     *     after a sucessful strong authentication request.
     * @param timeoutSec A timeout in seconds, after which this enrollment
     *     attempt is cancelled. Note that the client still needs to
     *     call revokeChallenge() to terminate the enrollment session.
     * @param requireAttention When set to true, requires user attention (e.g.
     *     eyes open and looking at the device) for enrollment to complete, as
     *     well as subsequent authentication. This is expected to be enabled by
     *     default to improve security and decrease falsing (unintentional face
     *     detection). This feature can be disabled at the user's request
     *     during enrollment, e.g. for accessibility reasons. When enabled,
     *     the FaceAcquiredInfo#POOR_GAZE message must be sent when the user's
     *     attention has not been established. The UI should inform the user
     *     to look at the device.
     * @return status The status of this method call.
     */
    @callflow(next={"cancel", "enroll", "revokeChallenge", "remove"})
    enroll(vec<uint8_t> hat, uint32_t timeoutSec, bool requireAttention)
        generates (Status status);

    /**
     * Finishes the secure transaction by invalidating the challenge generated
     * by generateChallenge().
     *
     * Clients must call this method once enrollment is complete, and the user's
     * face template no longer needs to be updated.
     *
     * @return status The status of this method call.
     */
    @callflow(next={"authenticate", "setActiveUser", "enumerate", "remove"})
    revokeChallenge() generates (Status status);

    /**
     * Requires that all subsequent authenticate calls to first have the
     * user's attention. This method does not affect enroll, which has its
     * own requireAttention parameter.
     *
     * Changes the state of previous enrollment setting. Because this may
     * decrease security, the user must enter their password before this method
     * is invoked (see @param HAT). The driver must verify the HAT before
     * changing the requireAttention state.
     * Note: In some cases it may not be possible to change the state of this
     * flag without re-enrolling. For example, if the user didn't provide
     * attention during the original enrollment. This flag reflects the same
     * persistent state as the one passed to enroll().
     *
     * @param requireAttention When set to true, requires user attention for
     *     authentication to succeed.
     * @param hat A valid Hardware Authentication Token, generated as a result
     *     of getChallenge().
     * @return status The status of this method call.
     */
    setRequireAttention(bool requireAttention, vec<uint8_t> hat)
        generates(Status status);

    /**
     * Retrieves the current requireAttention state.
     *
     * @return result, with its value parameter representing the current
     *     requireAttention state.
     */
    getRequireAttention(vec<uint8_t> hat) generates (OptionalBool result);

    /**
     * Returns an identifier associated with the current face set.
     *
     * The authenticator ID must change whenever a new face is enrolled. The
     * authenticator ID must not be changed when a face is deleted. The
     * authenticator ID must be an entropy-encoded random number which all
     * current templates are tied to. The authenticator ID must be immutable
     * outside of an active enrollment window to prevent replay attacks.
     *
     * @return result, with its value parameter representing an
     *     "authenticatorId": an identifier associated to the user's current
     *     face enrollment.
     */
    @callflow(next={"authenticate"})
    getAuthenticatorId() generates (OptionalUint64 result);

    /**
     * Cancels a pending enrollment or authentication request.
     *
     * @return status The status of this method call.
     */
    @callflow(next={"authenticate", "enroll", "enumerate", "remove",
        "setActiveUser"})
    cancel() generates (Status status);

    /**
     * Enumerates all face templates associated with the active user.
     *
     * The onEnumerate() callback method is invoked once for each face template
     * found.
     *
     * @return status The status of this method call.
     */
    @callflow(next={"remove", "enroll", "authenticate", "setActiveUser"})
    enumerate() generates (Status status);

    /**
     * Removes a face template or all face templates associated with the active
     * user.
     *
     * This method triggers the IBiometricsFaceClientCallback#onRemoved() method.
     *
     * @param faceId The id correpsonding to the face to be removed; or 0 if all
     *    faces are to be removed.
     * @return status The status of this method call.
     */
    @callflow(next={"enumerate", "authenticate", "cancel", "getAuthenticatorId",
        "setActiveUser"})
    remove(uint32_t faceId) generates (Status status);

    /**
     * Authenticates the active user.
     *
     * An optional operationId can be specified as a token from the transaction
     * being authorized.
     *
     * @param operationId A non-zero operation id associated with a crypto
     * object instance; or 0 if not being used.
     * @return status The status of this method call.
     */
    @callflow(next={"cancel", "generateChallenge", "remove"})
    authenticate(uint64_t operationId) generates (Status status);
};