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// Copyright 2017 Google Inc.
//
// 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 com.google.crypto.tink.mac;
import com.google.crypto.tink.CryptoFormat;
import com.google.crypto.tink.Mac;
import com.google.crypto.tink.PrimitiveSet;
import com.google.crypto.tink.PrimitiveWrapper;
import com.google.crypto.tink.Registry;
import com.google.crypto.tink.internal.MonitoringUtil;
import com.google.crypto.tink.internal.MutableMonitoringRegistry;
import com.google.crypto.tink.monitoring.MonitoringClient;
import com.google.crypto.tink.monitoring.MonitoringKeysetInfo;
import com.google.crypto.tink.proto.OutputPrefixType;
import com.google.crypto.tink.util.Bytes;
import java.security.GeneralSecurityException;
import java.util.Arrays;
import java.util.List;
import java.util.logging.Logger;
/**
* MacWrapper is the implementation of PrimitiveWrapper for the Mac primitive.
*
* <p>The returned primitive works with a keyset (rather than a single key). To compute a MAC tag,
* it uses the primary key in the keyset, and prepends to the tag a certain prefix associated with
* the primary key. To verify a tag, the primitive uses the prefix of the tag to efficiently select
* the right key in the set. If the keys associated with the prefix do not validate the tag, the
* primitive tries all keys with {@link com.google.crypto.tink.proto.OutputPrefixType#RAW}.
*/
class MacWrapper implements PrimitiveWrapper<Mac, Mac> {
private static final Logger logger = Logger.getLogger(MacWrapper.class.getName());
private static final byte[] FORMAT_VERSION = new byte[] {0};
private static final MacWrapper WRAPPER = new MacWrapper();
private static class WrappedMac implements Mac {
private final PrimitiveSet<Mac> primitives;
private final MonitoringClient.Logger computeLogger;
private final MonitoringClient.Logger verifyLogger;
private WrappedMac(PrimitiveSet<Mac> primitives) {
this.primitives = primitives;
if (primitives.hasAnnotations()) {
MonitoringClient client = MutableMonitoringRegistry.globalInstance().getMonitoringClient();
MonitoringKeysetInfo keysetInfo = MonitoringUtil.getMonitoringKeysetInfo(primitives);
computeLogger = client.createLogger(keysetInfo, "mac", "compute");
verifyLogger = client.createLogger(keysetInfo, "mac", "verify");
} else {
computeLogger = MonitoringUtil.DO_NOTHING_LOGGER;
verifyLogger = MonitoringUtil.DO_NOTHING_LOGGER;
}
}
@Override
public byte[] computeMac(final byte[] data) throws GeneralSecurityException {
byte[] data2 = data;
if (primitives.getPrimary().getOutputPrefixType().equals(OutputPrefixType.LEGACY)) {
data2 = com.google.crypto.tink.subtle.Bytes.concat(data, FORMAT_VERSION);
}
try {
byte[] output =
com.google.crypto.tink.subtle.Bytes.concat(
primitives.getPrimary().getIdentifier(),
primitives.getPrimary().getPrimitive().computeMac(data2));
computeLogger.log(primitives.getPrimary().getKeyId(), data2.length);
return output;
} catch (GeneralSecurityException e) {
computeLogger.logFailure();
throw e;
}
}
@Override
public void verifyMac(final byte[] mac, final byte[] data) throws GeneralSecurityException {
if (mac.length <= CryptoFormat.NON_RAW_PREFIX_SIZE) {
// This also rejects raw MAC with size of 4 bytes or fewer. Those MACs are
// clearly insecure, thus should be discouraged.
verifyLogger.logFailure();
throw new GeneralSecurityException("tag too short");
}
byte[] prefix = Arrays.copyOf(mac, CryptoFormat.NON_RAW_PREFIX_SIZE);
byte[] macNoPrefix = Arrays.copyOfRange(mac, CryptoFormat.NON_RAW_PREFIX_SIZE, mac.length);
List<PrimitiveSet.Entry<Mac>> entries = primitives.getPrimitive(prefix);
for (PrimitiveSet.Entry<Mac> entry : entries) {
byte[] data2 = data;
if (entry.getOutputPrefixType().equals(OutputPrefixType.LEGACY)) {
data2 = com.google.crypto.tink.subtle.Bytes.concat(data, FORMAT_VERSION);
}
try {
entry.getPrimitive().verifyMac(macNoPrefix, data2);
verifyLogger.log(entry.getKeyId(), data2.length);
// If there is no exception, the MAC is valid and we can return.
return;
} catch (GeneralSecurityException e) {
logger.info("tag prefix matches a key, but cannot verify: " + e);
// Ignored as we want to continue verification with the remaining keys.
}
}
// None "non-raw" key matched, so let's try the raw keys (if any exist).
entries = primitives.getRawPrimitives();
for (PrimitiveSet.Entry<Mac> entry : entries) {
try {
entry.getPrimitive().verifyMac(mac, data);
verifyLogger.log(entry.getKeyId(), data.length);
// If there is no exception, the MAC is valid and we can return.
return;
} catch (GeneralSecurityException ignored) {
// Ignored as we want to continue verification with other raw keys.
}
}
// nothing works.
verifyLogger.logFailure();
throw new GeneralSecurityException("invalid MAC");
}
}
private void validateMacKeyPrefixes(PrimitiveSet<Mac> primitives)
throws GeneralSecurityException {
for (List<PrimitiveSet.Entry<Mac>> entryList : primitives.getAll()) {
for (PrimitiveSet.Entry<Mac> entry : entryList) {
if (entry.getKey() instanceof MacKey) {
MacKey macKey = (MacKey) entry.getKey();
Bytes expectedOutputPrefix = Bytes.copyFrom(entry.getIdentifier());
if (!expectedOutputPrefix.equals(macKey.getOutputPrefix())) {
throw new GeneralSecurityException(
"Mac Key with parameters "
+ macKey.getParameters()
+ " has wrong output prefix ("
+ macKey.getOutputPrefix()
+ ") instead of ("
+ expectedOutputPrefix
+ ")");
}
}
}
}
}
MacWrapper() {}
@Override
public Mac wrap(final PrimitiveSet<Mac> primitives) throws GeneralSecurityException {
validateMacKeyPrefixes(primitives);
return new WrappedMac(primitives);
}
@Override
public Class<Mac> getPrimitiveClass() {
return Mac.class;
}
@Override
public Class<Mac> getInputPrimitiveClass() {
return Mac.class;
}
public static void register() throws GeneralSecurityException {
Registry.registerPrimitiveWrapper(WRAPPER);
}
}
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