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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.aead;
import com.google.crypto.tink.Aead;
import com.google.crypto.tink.CryptoFormat;
import com.google.crypto.tink.KeyManager;
import com.google.crypto.tink.KeysetHandle;
import com.google.crypto.tink.PrimitiveSet;
import com.google.crypto.tink.Registry;
import com.google.crypto.tink.subtle.Bytes;
import java.security.GeneralSecurityException;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.logging.Logger;
/**
* Static methods for obtaining {@link Aead} instances.
*
* Usage
*
* {@code
* KeysetHandle keysetHandle = ...;
* Aead aead = AeadFactory.getPrimitive(keysetHandle);
* byte[] plaintext = ...;
* byte[] aad = ...;
* byte[] ciphertext = aead.encrypt(plaintext, aad);
* }
*
* The returned primitive works with a keyset (rather than a single key). To encrypt a plaintext,
* it uses the primary key in the keyset, and prepends to the ciphertext a certain prefix associated
* with the primary key. To decrypt, the primitive uses the prefix of the ciphertext to efficiently
* select the right key in the set. If the keys associated with the prefix do not work, the
* primitive tries all keys with {@link com.google.crypto.tink.proto.OutputPrefixType#RAW}.
*
* @since 1.0.0
*/
public final class AeadFactory {
private static final Logger logger = Logger.getLogger(AeadFactory.class.getName());
/**
* @return a Aead primitive from a {@code keysetHandle}.
* @throws GeneralSecurityException
*/
public static Aead getPrimitive(KeysetHandle keysetHandle) throws GeneralSecurityException {
return getPrimitive(keysetHandle, /* keyManager= */ null);
}
/**
* @return a Aead primitive from a {@code keysetHandle} and a custom {@code keyManager}.
* @throws GeneralSecurityException
*/
public static Aead getPrimitive(KeysetHandle keysetHandle, final KeyManager keyManager)
throws GeneralSecurityException {
final PrimitiveSet pset = Registry.getPrimitives(keysetHandle, keyManager);
validate(pset);
return new Aead() {
@Override
public byte[] encrypt(final byte[] plaintext, final byte[] associatedData)
throws GeneralSecurityException {
return Bytes.concat(
pset.getPrimary().getIdentifier(),
pset.getPrimary().getPrimitive().encrypt(plaintext, associatedData));
}
@Override
public byte[] decrypt(final byte[] ciphertext, final byte[] associatedData)
throws GeneralSecurityException {
if (ciphertext.length > CryptoFormat.NON_RAW_PREFIX_SIZE) {
byte[] prefix = Arrays.copyOfRange(ciphertext, 0, CryptoFormat.NON_RAW_PREFIX_SIZE);
byte[] ciphertextNoPrefix =
Arrays.copyOfRange(ciphertext, CryptoFormat.NON_RAW_PREFIX_SIZE, ciphertext.length);
List> entries = pset.getPrimitive(prefix);
for (PrimitiveSet.Entry entry : entries) {
try {
return entry.getPrimitive().decrypt(ciphertextNoPrefix, associatedData);
} catch (GeneralSecurityException e) {
logger.info("ciphertext prefix matches a key, but cannot decrypt: " + e.toString());
continue;
}
}
}
// Let's try all RAW keys.
List> entries = pset.getRawPrimitives();
for (PrimitiveSet.Entry entry : entries) {
try {
return entry.getPrimitive().decrypt(ciphertext, associatedData);
} catch (GeneralSecurityException e) {
continue;
}
}
// nothing works.
throw new GeneralSecurityException("decryption failed");
}
};
}
// Check that all primitives in pset are Aead instances.
private static void validate(final PrimitiveSet pset) throws GeneralSecurityException {
for (Collection> entries : pset.getAll()) {
for (PrimitiveSet.Entry entry : entries) {
if (!(entry.getPrimitive() instanceof Aead)) {
throw new GeneralSecurityException("invalid AEAD key material");
}
}
}
}
}