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/*
* Copyright (C) 2021 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.keystore2;
import android.security.keymaster.KeymasterArguments;
import android.security.keymaster.KeymasterDefs;
import android.security.keystore.KeyProperties;
import java.security.ProviderException;
/**
* @hide
*/
public abstract class KeymasterUtils {
private KeymasterUtils() {}
/** @hide */
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);
}
}
/** @hide */
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);
}
}
/** @hide */
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 {@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;
}
}
}
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