keymaster/aidl/android/hardware/keymaster/VerificationToken.aidl

/*
 * Copyright (C) 2020 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.keymaster;

import android.hardware.keymaster.SecurityLevel;
import android.hardware.keymaster.Timestamp;

/**
 * VerificationToken instances are used for secure environments to authenticate one another.
 *
 * This version of the parcelable currently don't use the parametersVerified field since it's not
 * needed for time-based verification. This can be added in a later version, if needed.
 * @hide
 */
@VintfStability
parcelable VerificationToken {
    /**
     * The operation handle, used to ensure freshness.
     */
    long challenge;

    /**
     * The current time of the secure environment that generates the VerificationToken.  This can be
     * checked against auth tokens generated by the same secure environment, which avoids needing to
     * synchronize clocks.
     */
    Timestamp timestamp;

    /**
     * SecurityLevel of the secure environment that generated the token.
     */
    SecurityLevel securityLevel = SecurityLevel.SOFTWARE;

    /**
     * 32-byte HMAC-SHA256 of the above values, computed as:
     *
     *    HMAC(H,
     *         "Auth Verification" || challenge || timestamp || securityLevel || parametersVerified)
     *
     * where:
     *
     *   ``HMAC'' is the shared HMAC key (see computeSharedHmac() in IKeymaster).
     *
     *   ``||'' represents concatenation
     *
     * The representation of challenge and timestamp is as 64-bit unsigned integers in big-endian
     * order.  securityLevel is represented as a 32-bit unsigned integer in big-endian order.
     *
     * If parametersVerified is non-empty, the representation of parametersVerified is an ASN.1 DER
     * encoded representation of the values.  The ASN.1 schema used is the AuthorizationList schema
     * from the Keystore attestation documentation.  If parametersVerified is empty, it is simply
     * omitted from the HMAC computation.
     */
    byte[] mac;
}