keystore/java/android/security/KeyStoreParameter.java

/*
 * Copyright (C) 2013 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.security;

import android.content.Context;

import java.security.KeyPairGenerator;
import java.security.KeyStore.ProtectionParameter;

/**
 * This provides the optional parameters that can be specified for
 * {@code KeyStore} entries that work with
 * <a href="{@docRoot}training/articles/keystore.html">Android KeyStore
 * facility</a>. The Android KeyStore facility is accessed through a
 * {@link java.security.KeyStore} API using the {@code AndroidKeyStore}
 * provider. The {@code context} passed in may be used to pop up some UI to ask
 * the user to unlock or initialize the Android KeyStore facility.
 * <p>
 * Any entries placed in the {@code KeyStore} may be retrieved later. Note that
 * there is only one logical instance of the {@code KeyStore} per application
 * UID so apps using the {@code sharedUid} facility will also share a
 * {@code KeyStore}.
 * <p>
 * Keys may be generated using the {@link KeyPairGenerator} facility with a
 * {@link KeyPairGeneratorSpec} to specify the entry's {@code alias}. A
 * self-signed X.509 certificate will be attached to generated entries, but that
 * may be replaced at a later time by a certificate signed by a real Certificate
 * Authority.
 */
public final class KeyStoreParameter implements ProtectionParameter {
    private int mFlags;

    private KeyStoreParameter(int flags) {
        mFlags = flags;
    }

    /**
     * @hide
     */
    public int getFlags() {
        return mFlags;
    }

    /**
     * Returns {@code true} if this parameter requires entries to be encrypted
     * on the disk.
     */
    public boolean isEncryptionRequired() {
        return (mFlags & KeyStore.FLAG_ENCRYPTED) != 0;
    }

    /**
     * Builder class for {@link KeyStoreParameter} objects.
     * <p>
     * This will build protection parameters for use with the
     * <a href="{@docRoot}training/articles/keystore.html">Android KeyStore
     * facility</a>.
     * <p>
     * This can be used to require that KeyStore entries be stored encrypted.
     * <p>
     * Example:
     *
     * <pre class="prettyprint">
     * KeyStoreParameter params = new KeyStoreParameter.Builder(mContext)
     *         .setEncryptionRequired()
     *         .build();
     * </pre>
     */
    public final static class Builder {
        private int mFlags;

        /**
         * Creates a new instance of the {@code Builder} with the given
         * {@code context}. The {@code context} passed in may be used to pop up
         * some UI to ask the user to unlock or initialize the Android KeyStore
         * facility.
         */
        public Builder(Context context) {
            if (context == null) {
                throw new NullPointerException("context == null");
            }

            // Context is currently not used, but will be in the future.
        }

        /**
         * Indicates that this key must be encrypted at rest on storage. Note
         * that enabling this will require that the user enable a strong lock
         * screen (e.g., PIN, password) before creating or using the generated
         * key is successful.
         */
        public Builder setEncryptionRequired(boolean required) {
            if (required) {
                mFlags |= KeyStore.FLAG_ENCRYPTED;
            } else {
                mFlags &= ~KeyStore.FLAG_ENCRYPTED;
            }
            return this;
        }

        /**
         * Builds the instance of the {@code KeyPairGeneratorSpec}.
         *
         * @throws IllegalArgumentException if a required field is missing
         * @return built instance of {@code KeyPairGeneratorSpec}
         */
        public KeyStoreParameter build() {
            return new KeyStoreParameter(mFlags);
        }
    }
}