/*
* Copyright (C) 2015 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.keystore;
import android.hardware.fingerprint.FingerprintManager;
import android.security.GateKeeper;
import android.security.KeyStore;
import android.security.keymaster.KeymasterArguments;
import android.security.keymaster.KeymasterDefs;
import java.security.ProviderException;
/**
* @hide
*/
public abstract class KeymasterUtils {
private KeymasterUtils() {}
public static int getDigestOutputSizeBits(int keymasterDigest) {
switch (keymasterDigest) {
case KeymasterDefs.KM_DIGEST_NONE:
return -1;
case KeymasterDefs.KM_DIGEST_MD5:
return 128;
case KeymasterDefs.KM_DIGEST_SHA1:
return 160;
case KeymasterDefs.KM_DIGEST_SHA_2_224:
return 224;
case KeymasterDefs.KM_DIGEST_SHA_2_256:
return 256;
case KeymasterDefs.KM_DIGEST_SHA_2_384:
return 384;
case KeymasterDefs.KM_DIGEST_SHA_2_512:
return 512;
default:
throw new IllegalArgumentException("Unknown digest: " + keymasterDigest);
}
}
public static boolean isKeymasterBlockModeIndCpaCompatibleWithSymmetricCrypto(
int keymasterBlockMode) {
switch (keymasterBlockMode) {
case KeymasterDefs.KM_MODE_ECB:
return false;
case KeymasterDefs.KM_MODE_CBC:
case KeymasterDefs.KM_MODE_CTR:
case KeymasterDefs.KM_MODE_GCM:
return true;
default:
throw new IllegalArgumentException("Unsupported block mode: " + keymasterBlockMode);
}
}
public static boolean isKeymasterPaddingSchemeIndCpaCompatibleWithAsymmetricCrypto(
int keymasterPadding) {
switch (keymasterPadding) {
case KeymasterDefs.KM_PAD_NONE:
return false;
case KeymasterDefs.KM_PAD_RSA_OAEP:
case KeymasterDefs.KM_PAD_RSA_PKCS1_1_5_ENCRYPT:
return true;
default:
throw new IllegalArgumentException(
"Unsupported asymmetric encryption padding scheme: " + keymasterPadding);
}
}
/**
* Adds keymaster arguments to express the key's authorization policy supported by user
* authentication.
*
* @param userAuthenticationRequired whether user authentication is required to authorize the
* use of the key.
* @param userAuthenticationValidityDurationSeconds duration of time (seconds) for which user
* authentication is valid as authorization for using the key or {@code -1} if every
* use of the key needs authorization.
*
* @throws IllegalStateException if user authentication is required but the system is in a wrong
* state (e.g., secure lock screen not set up) for generating or importing keys that
* require user authentication.
*/
public static void addUserAuthArgs(KeymasterArguments args,
boolean userAuthenticationRequired,
int userAuthenticationValidityDurationSeconds,
boolean userAuthenticationValidWhileOnBody,
boolean invalidatedByBiometricEnrollment) {
if (!userAuthenticationRequired) {
args.addBoolean(KeymasterDefs.KM_TAG_NO_AUTH_REQUIRED);
return;
}
if (userAuthenticationValidityDurationSeconds == -1) {
// Every use of this key needs to be authorized by the user. This currently means
// fingerprint-only auth.
FingerprintManager fingerprintManager =
KeyStore.getApplicationContext().getSystemService(FingerprintManager.class);
// TODO: Restore USE_FINGERPRINT permission check in
// FingerprintManager.getAuthenticatorId once the ID is no longer needed here.
long fingerprintOnlySid =
(fingerprintManager != null) ? fingerprintManager.getAuthenticatorId() : 0;
if (fingerprintOnlySid == 0) {
throw new IllegalStateException(
"At least one fingerprint must be enrolled to create keys requiring user"
+ " authentication for every use");
}
long sid;
if (invalidatedByBiometricEnrollment) {
// The fingerprint-only SID will change on fingerprint enrollment or removal of all,
// enrolled fingerprints, invalidating the key.
sid = fingerprintOnlySid;
} else {
// The root SID will *not* change on fingerprint enrollment, or removal of all
// enrolled fingerprints, allowing the key to remain valid.
sid = getRootSid();
}
args.addUnsignedLong(
KeymasterDefs.KM_TAG_USER_SECURE_ID, KeymasterArguments.toUint64(sid));
args.addEnum(KeymasterDefs.KM_TAG_USER_AUTH_TYPE, KeymasterDefs.HW_AUTH_FINGERPRINT);
if (userAuthenticationValidWhileOnBody) {
throw new ProviderException("Key validity extension while device is on-body is not "
+ "supported for keys requiring fingerprint authentication");
}
} else {
// The key is authorized for use for the specified amount of time after the user has
// authenticated. Whatever unlocks the secure lock screen should authorize this key.
long rootSid = getRootSid();
args.addUnsignedLong(KeymasterDefs.KM_TAG_USER_SECURE_ID,
KeymasterArguments.toUint64(rootSid));
args.addEnum(KeymasterDefs.KM_TAG_USER_AUTH_TYPE,
KeymasterDefs.HW_AUTH_PASSWORD | KeymasterDefs.HW_AUTH_FINGERPRINT);
args.addUnsignedInt(KeymasterDefs.KM_TAG_AUTH_TIMEOUT,
userAuthenticationValidityDurationSeconds);
if (userAuthenticationValidWhileOnBody) {
args.addBoolean(KeymasterDefs.KM_TAG_ALLOW_WHILE_ON_BODY);
}
}
}
/**
* Adds {@code KM_TAG_MIN_MAC_LENGTH} tag, if necessary, to the keymaster arguments for
* generating or importing a key. This tag may only be needed for symmetric keys (e.g., HMAC,
* AES-GCM).
*/
public static void addMinMacLengthAuthorizationIfNecessary(KeymasterArguments args,
int keymasterAlgorithm,
int[] keymasterBlockModes,
int[] keymasterDigests) {
switch (keymasterAlgorithm) {
case KeymasterDefs.KM_ALGORITHM_AES:
if (com.android.internal.util.ArrayUtils.contains(
keymasterBlockModes, KeymasterDefs.KM_MODE_GCM)) {
// AES GCM key needs the minimum length of AEAD tag specified.
args.addUnsignedInt(KeymasterDefs.KM_TAG_MIN_MAC_LENGTH,
AndroidKeyStoreAuthenticatedAESCipherSpi.GCM
.MIN_SUPPORTED_TAG_LENGTH_BITS);
}
break;
case KeymasterDefs.KM_ALGORITHM_HMAC:
// HMAC key needs the minimum length of MAC set to the output size of the associated
// digest. This is because we do not offer a way to generate shorter MACs and
// don't offer a way to verify MACs (other than by generating them).
if (keymasterDigests.length != 1) {
throw new ProviderException(
"Unsupported number of authorized digests for HMAC key: "
+ keymasterDigests.length
+ ". Exactly one digest must be authorized");
}
int keymasterDigest = keymasterDigests[0];
int digestOutputSizeBits = getDigestOutputSizeBits(keymasterDigest);
if (digestOutputSizeBits == -1) {
throw new ProviderException(
"HMAC key authorized for unsupported digest: "
+ KeyProperties.Digest.fromKeymaster(keymasterDigest));
}
args.addUnsignedInt(KeymasterDefs.KM_TAG_MIN_MAC_LENGTH, digestOutputSizeBits);
break;
}
}
private static long getRootSid() {
long rootSid = GateKeeper.getSecureUserId();
if (rootSid == 0) {
throw new IllegalStateException("Secure lock screen must be enabled"
+ " to create keys requiring user authentication");
}
return rootSid;
}
}