458 lines
18 KiB
Java
458 lines
18 KiB
Java
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.security;
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import android.content.Context;
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import android.text.TextUtils;
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import java.security.spec.AlgorithmParameterSpec;
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import java.util.Date;
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import javax.crypto.Cipher;
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import javax.crypto.KeyGenerator;
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import javax.crypto.SecretKey;
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/**
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* {@link AlgorithmParameterSpec} for initializing a {@code KeyGenerator} that works with
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* <a href="{@docRoot}training/articles/keystore.html">Android KeyStore facility</a>.
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*
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* <p>The Android KeyStore facility is accessed through a {@link KeyGenerator} API using the
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* {@code AndroidKeyStore} provider. The {@code context} passed in may be used to pop up some UI to
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* ask the user to unlock or initialize the Android KeyStore facility.
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*
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* <p>After generation, the {@code keyStoreAlias} is used with the
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* {@link java.security.KeyStore#getEntry(String, java.security.KeyStore.ProtectionParameter)}
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* interface to retrieve the {@link SecretKey}.
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*
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* @hide
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*/
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public class KeyGeneratorSpec implements AlgorithmParameterSpec {
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private final Context mContext;
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private final String mKeystoreAlias;
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private final int mFlags;
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private final Integer mKeySize;
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private final Date mKeyValidityStart;
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private final Date mKeyValidityForOriginationEnd;
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private final Date mKeyValidityForConsumptionEnd;
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private final @KeyStoreKeyConstraints.PurposeEnum int mPurposes;
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private final @KeyStoreKeyConstraints.PaddingEnum int mPaddings;
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private final @KeyStoreKeyConstraints.BlockModeEnum int mBlockModes;
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private final boolean mRandomizedEncryptionRequired;
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private final @KeyStoreKeyConstraints.UserAuthenticatorEnum int mUserAuthenticators;
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private final int mUserAuthenticationValidityDurationSeconds;
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private KeyGeneratorSpec(
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Context context,
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String keyStoreAlias,
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int flags,
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Integer keySize,
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Date keyValidityStart,
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Date keyValidityForOriginationEnd,
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Date keyValidityForConsumptionEnd,
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@KeyStoreKeyConstraints.PurposeEnum int purposes,
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@KeyStoreKeyConstraints.PaddingEnum int paddings,
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@KeyStoreKeyConstraints.BlockModeEnum int blockModes,
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boolean randomizedEncryptionRequired,
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@KeyStoreKeyConstraints.UserAuthenticatorEnum int userAuthenticators,
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int userAuthenticationValidityDurationSeconds) {
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if (context == null) {
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throw new IllegalArgumentException("context == null");
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} else if (TextUtils.isEmpty(keyStoreAlias)) {
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throw new IllegalArgumentException("keyStoreAlias must not be empty");
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} else if ((userAuthenticationValidityDurationSeconds < 0)
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&& (userAuthenticationValidityDurationSeconds != -1)) {
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throw new IllegalArgumentException(
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"userAuthenticationValidityDurationSeconds must not be negative");
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}
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mContext = context;
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mKeystoreAlias = keyStoreAlias;
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mFlags = flags;
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mKeySize = keySize;
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mKeyValidityStart = keyValidityStart;
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mKeyValidityForOriginationEnd = keyValidityForOriginationEnd;
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mKeyValidityForConsumptionEnd = keyValidityForConsumptionEnd;
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mPurposes = purposes;
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mPaddings = paddings;
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mBlockModes = blockModes;
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mRandomizedEncryptionRequired = randomizedEncryptionRequired;
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mUserAuthenticators = userAuthenticators;
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mUserAuthenticationValidityDurationSeconds = userAuthenticationValidityDurationSeconds;
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}
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/**
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* Gets the Android context used for operations with this instance.
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*/
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public Context getContext() {
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return mContext;
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}
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/**
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* Returns the alias that will be used in the {@code java.security.KeyStore} in conjunction with
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* the {@code AndroidKeyStore}.
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*/
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public String getKeystoreAlias() {
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return mKeystoreAlias;
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}
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/**
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* @hide
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*/
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public int getFlags() {
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return mFlags;
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}
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/**
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* Gets the requested key size or {@code null} if the default size should be used.
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*/
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public Integer getKeySize() {
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return mKeySize;
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}
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/**
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* Gets the time instant before which the key is not yet valid.
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*
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* @return instant or {@code null} if not restricted.
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*/
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public Date getKeyValidityStart() {
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return mKeyValidityStart;
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}
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/**
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* Gets the time instant after which the key is no longer valid for decryption and verification.
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*
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* @return instant or {@code null} if not restricted.
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*/
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public Date getKeyValidityForConsumptionEnd() {
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return mKeyValidityForConsumptionEnd;
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}
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/**
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* Gets the time instant after which the key is no longer valid for encryption and signing.
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*
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* @return instant or {@code null} if not restricted.
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*/
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public Date getKeyValidityForOriginationEnd() {
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return mKeyValidityForOriginationEnd;
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}
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/**
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* Gets the set of purposes for which the key can be used.
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*/
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public @KeyStoreKeyConstraints.PurposeEnum int getPurposes() {
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return mPurposes;
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}
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/**
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* Gets the set of padding schemes to which the key is restricted.
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*/
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public @KeyStoreKeyConstraints.PaddingEnum int getPaddings() {
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return mPaddings;
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}
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/**
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* Gets the set of block modes to which the key is restricted.
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*/
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public @KeyStoreKeyConstraints.BlockModeEnum int getBlockModes() {
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return mBlockModes;
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}
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/**
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* Returns {@code true} if encryption using this key must be sufficiently randomized to produce
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* different ciphertexts for the same plaintext every time. The formal cryptographic property
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* being required is <em>indistinguishability under chosen-plaintext attack ({@code
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* IND-CPA})</em>. This property is important because it mitigates several classes of
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* weaknesses due to which ciphertext may leak information about plaintext. For example, if a
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* given plaintext always produces the same ciphertext, an attacker may see the repeated
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* ciphertexts and be able to deduce something about the plaintext.
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*/
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public boolean isRandomizedEncryptionRequired() {
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return mRandomizedEncryptionRequired;
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}
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/**
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* Gets the set of user authenticators which protect access to this key. The key can only be
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* used iff the user has authenticated to at least one of these user authenticators.
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*
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* @return user authenticators or {@code 0} if the key can be used without user authentication.
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*/
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public @KeyStoreKeyConstraints.UserAuthenticatorEnum int getUserAuthenticators() {
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return mUserAuthenticators;
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}
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/**
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* Gets the duration of time (seconds) for which this key can be used after the user
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* successfully authenticates to one of the associated user authenticators.
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*
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* @return duration in seconds or {@code -1} if not restricted. {@code 0} means authentication
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* is required for every use of the key.
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*/
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public int getUserAuthenticationValidityDurationSeconds() {
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return mUserAuthenticationValidityDurationSeconds;
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}
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/**
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* Returns {@code true} if the key must be encrypted in the {@link java.security.KeyStore}.
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*/
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public boolean isEncryptionRequired() {
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return (mFlags & KeyStore.FLAG_ENCRYPTED) != 0;
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}
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public static class Builder {
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private final Context mContext;
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private String mKeystoreAlias;
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private int mFlags;
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private Integer mKeySize;
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private Date mKeyValidityStart;
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private Date mKeyValidityForOriginationEnd;
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private Date mKeyValidityForConsumptionEnd;
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private @KeyStoreKeyConstraints.PurposeEnum int mPurposes;
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private @KeyStoreKeyConstraints.PaddingEnum int mPaddings;
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private @KeyStoreKeyConstraints.BlockModeEnum int mBlockModes;
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private boolean mRandomizedEncryptionRequired = true;
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private @KeyStoreKeyConstraints.UserAuthenticatorEnum int mUserAuthenticators;
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private int mUserAuthenticationValidityDurationSeconds = -1;
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/**
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* Creates a new instance of the {@code Builder} with the given {@code context}. The
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* {@code context} passed in may be used to pop up some UI to ask the user to unlock or
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* initialize the Android KeyStore facility.
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*/
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public Builder(Context context) {
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if (context == null) {
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throw new NullPointerException("context == null");
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}
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mContext = context;
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}
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/**
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* Sets the alias to be used to retrieve the key later from a {@link java.security.KeyStore}
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* instance using the {@code AndroidKeyStore} provider.
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*
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* <p>The alias must be provided. There is no default.
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*/
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public Builder setAlias(String alias) {
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if (alias == null) {
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throw new NullPointerException("alias == null");
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}
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mKeystoreAlias = alias;
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return this;
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}
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/**
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* Sets the size (in bits) of the key to be generated.
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*
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* <p>By default, the key size will be determines based on the key algorithm. For example,
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* for {@code HmacSHA256}, the key size will default to {@code 256}.
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*/
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public Builder setKeySize(int keySize) {
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mKeySize = keySize;
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return this;
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}
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/**
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* Indicates that this key must be encrypted at rest on storage. Note that enabling this
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* will require that the user enable a strong lock screen (e.g., PIN, password) before
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* creating or using the generated key is successful.
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*/
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public Builder setEncryptionRequired(boolean required) {
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if (required) {
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mFlags |= KeyStore.FLAG_ENCRYPTED;
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} else {
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mFlags &= ~KeyStore.FLAG_ENCRYPTED;
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}
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return this;
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}
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/**
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* Sets the time instant before which the key is not yet valid.
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*
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* <p>By default, the key is valid at any instant.
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*
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* @see #setKeyValidityEnd(Date)
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*/
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public Builder setKeyValidityStart(Date startDate) {
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mKeyValidityStart = startDate;
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return this;
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}
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/**
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* Sets the time instant after which the key is no longer valid.
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*
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* <p>By default, the key is valid at any instant.
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*
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* @see #setKeyValidityStart(Date)
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* @see #setKeyValidityForConsumptionEnd(Date)
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* @see #setKeyValidityForOriginationEnd(Date)
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*/
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public Builder setKeyValidityEnd(Date endDate) {
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setKeyValidityForOriginationEnd(endDate);
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setKeyValidityForConsumptionEnd(endDate);
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return this;
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}
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/**
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* Sets the time instant after which the key is no longer valid for encryption and signing.
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*
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* <p>By default, the key is valid at any instant.
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*
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* @see #setKeyValidityForConsumptionEnd(Date)
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*/
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public Builder setKeyValidityForOriginationEnd(Date endDate) {
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mKeyValidityForOriginationEnd = endDate;
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return this;
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}
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/**
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* Sets the time instant after which the key is no longer valid for decryption and
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* verification.
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*
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* <p>By default, the key is valid at any instant.
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*
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* @see #setKeyValidityForOriginationEnd(Date)
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*/
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public Builder setKeyValidityForConsumptionEnd(Date endDate) {
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mKeyValidityForConsumptionEnd = endDate;
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return this;
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}
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/**
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* Restricts the key to being used only for the provided set of purposes.
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*
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* <p>This restriction must be specified. There is no default.
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*/
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public Builder setPurposes(@KeyStoreKeyConstraints.PurposeEnum int purposes) {
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mPurposes = purposes;
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return this;
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}
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/**
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* Restricts the key to being used only with the provided padding schemes. Attempts to use
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* the key with any other padding will be rejected.
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*
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* <p>This restriction must be specified for keys which are used for encryption/decryption.
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*/
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public Builder setPaddings(@KeyStoreKeyConstraints.PaddingEnum int paddings) {
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mPaddings = paddings;
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return this;
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}
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/**
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* Restricts the key to being used only with the provided block modes. Attempts to use the
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* key with any other block modes will be rejected.
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*
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* <p>This restriction must be specified for keys which are used for encryption/decryption.
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*/
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public Builder setBlockModes(@KeyStoreKeyConstraints.BlockModeEnum int blockModes) {
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mBlockModes = blockModes;
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return this;
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}
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/**
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* Sets whether encryption using this key must be sufficiently randomized to produce
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* different ciphertexts for the same plaintext every time. The formal cryptographic
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* property being required is <em>indistinguishability under chosen-plaintext attack
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* ({@code IND-CPA})</em>. This property is important because it mitigates several classes
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* of weaknesses due to which ciphertext may leak information about plaintext. For example,
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* if a given plaintext always produces the same ciphertext, an attacker may see the
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* repeated ciphertexts and be able to deduce something about the plaintext.
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*
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* <p>By default, {@code IND-CPA} is required.
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*
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* <p>When {@code IND-CPA} is required:
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* <ul>
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* <li>block modes which do not offer {@code IND-CPA}, such as {@code ECB}, are prohibited;
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* </li>
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* <li>in block modes which use an IV, such as {@code CBC}, {@code CTR}, and {@code GCM},
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* caller-provided IVs are rejected when encrypting, to ensure that only random IVs are
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* used.</li>
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*
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* <p>Before disabling this requirement, consider the following approaches instead:
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* <ul>
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* <li>If you are generating a random IV for encryption and then initializing a {@code}
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* Cipher using the IV, the solution is to let the {@code Cipher} generate a random IV
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* instead. This will occur if the {@code Cipher} is initialized for encryption without an
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* IV. The IV can then be queried via {@link Cipher#getIV()}.</li>
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* <li>If you are generating a non-random IV (e.g., an IV derived from something not fully
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* random, such as the name of the file being encrypted, or transaction ID, or password,
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* or a device identifier), consider changing your design to use a random IV which will then
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* be provided in addition to the ciphertext to the entities which need to decrypt the
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* ciphertext.</li>
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* </ul>
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*/
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public Builder setRandomizedEncryptionRequired(boolean required) {
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mRandomizedEncryptionRequired = required;
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return this;
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}
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/**
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* Sets the user authenticators which protect access to this key. The key can only be used
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* iff the user has authenticated to at least one of these user authenticators.
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*
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* <p>By default, the key can be used without user authentication.
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*
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* @param userAuthenticators user authenticators or empty list if this key can be accessed
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* without user authentication.
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*
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* @see #setUserAuthenticationValidityDurationSeconds(int)
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*/
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public Builder setUserAuthenticators(
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@KeyStoreKeyConstraints.UserAuthenticatorEnum int userAuthenticators) {
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mUserAuthenticators = userAuthenticators;
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return this;
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}
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/**
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* Sets the duration of time (seconds) for which this key can be used after the user
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* successfully authenticates to one of the associated user authenticators.
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*
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* <p>By default, the user needs to authenticate for every use of the key.
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*
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* @param seconds duration in seconds or {@code 0} if the user needs to authenticate for
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* every use of the key.
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*
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* @see #setUserAuthenticators(int)
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*/
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public Builder setUserAuthenticationValidityDurationSeconds(int seconds) {
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mUserAuthenticationValidityDurationSeconds = seconds;
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return this;
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}
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/**
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* Builds a new instance instance of {@code KeyGeneratorSpec}.
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*
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* @throws IllegalArgumentException if a required field is missing or violates a constraint.
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*/
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public KeyGeneratorSpec build() {
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return new KeyGeneratorSpec(mContext,
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mKeystoreAlias,
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mFlags,
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mKeySize,
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mKeyValidityStart,
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mKeyValidityForOriginationEnd,
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mKeyValidityForConsumptionEnd,
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mPurposes,
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mPaddings,
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mBlockModes,
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mRandomizedEncryptionRequired,
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mUserAuthenticators,
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mUserAuthenticationValidityDurationSeconds);
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}
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}
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}
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