Add AesEcbSingleBlockEncryption.java.
Test: Unit Tests.
Bug: 200231384
Change-Id: I3438f6c0380a464ed42140f8712d3cf14c883ab9
diff --git a/nearby/service/java/com/android/server/nearby/common/bluetooth/fastpair/AesEcbSingleBlockEncryption.java b/nearby/service/java/com/android/server/nearby/common/bluetooth/fastpair/AesEcbSingleBlockEncryption.java
new file mode 100644
index 0000000..547931e
--- /dev/null
+++ b/nearby/service/java/com/android/server/nearby/common/bluetooth/fastpair/AesEcbSingleBlockEncryption.java
@@ -0,0 +1,78 @@
+/*
+ * Copyright 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 com.android.server.nearby.common.bluetooth.fastpair;
+
+import android.annotation.SuppressLint;
+
+import java.security.GeneralSecurityException;
+import java.security.NoSuchAlgorithmException;
+
+import javax.crypto.Cipher;
+import javax.crypto.KeyGenerator;
+import javax.crypto.spec.SecretKeySpec;
+
+/**
+ * Utilities used for encrypting and decrypting Fast Pair packets.
+ */
+// SuppressLint for ""ecb encryption mode should not be used".
+// Reasons:
+// 1. FastPair data is guaranteed to be only 1 AES block in size, ECB is secure.
+// 2. In each case, the encrypted data is less than 16-bytes and is
+// padded up to 16-bytes using random data to fill the rest of the byte array,
+// so the plaintext will never be the same.
+@SuppressLint("GetInstance")
+public final class AesEcbSingleBlockEncryption {
+
+ public static final int AES_BLOCK_LENGTH = 16;
+ public static final int KEY_LENGTH = 16;
+
+ private AesEcbSingleBlockEncryption() {
+ }
+
+ /**
+ * Generates a 16-byte AES key.
+ */
+ public static byte[] generateKey() throws NoSuchAlgorithmException {
+ KeyGenerator generator = KeyGenerator.getInstance("AES");
+ generator.init(KEY_LENGTH * 8); // Ensure a 16-byte key is always used.
+ return generator.generateKey().getEncoded();
+ }
+
+ /**
+ * Encrypts data with the provided secret.
+ */
+ public static byte[] encrypt(byte[] secret, byte[] data) throws GeneralSecurityException {
+ return doEncryption(Cipher.ENCRYPT_MODE, secret, data);
+ }
+
+ /**
+ * Decrypts data with the provided secret.
+ */
+ public static byte[] decrypt(byte[] secret, byte[] data) throws GeneralSecurityException {
+ return doEncryption(Cipher.DECRYPT_MODE, secret, data);
+ }
+
+ private static byte[] doEncryption(int mode, byte[] secret, byte[] data)
+ throws GeneralSecurityException {
+ if (data.length != AES_BLOCK_LENGTH) {
+ throw new IllegalArgumentException("This encrypter only supports 16-byte inputs.");
+ }
+ Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");
+ cipher.init(mode, new SecretKeySpec(secret, "AES"));
+ return cipher.doFinal(data);
+ }
+}
diff --git a/nearby/tests/src/com/android/server/nearby/common/bluetooth/fastpair/AesEcbSingleBlockEncryptionTest.java b/nearby/tests/src/com/android/server/nearby/common/bluetooth/fastpair/AesEcbSingleBlockEncryptionTest.java
new file mode 100644
index 0000000..0e13133
--- /dev/null
+++ b/nearby/tests/src/com/android/server/nearby/common/bluetooth/fastpair/AesEcbSingleBlockEncryptionTest.java
@@ -0,0 +1,62 @@
+/*
+ * 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 com.android.server.nearby.common.bluetooth.fastpair;
+
+import static com.google.common.io.BaseEncoding.base16;
+import static com.google.common.truth.Truth.assertThat;
+
+import android.platform.test.annotations.Presubmit;
+
+import androidx.test.filters.SmallTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import com.google.common.primitives.Bytes;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit tests for {@link AesEcbSingleBlockEncryption}. */
+@Presubmit
+@SmallTest
+@RunWith(AndroidJUnit4.class)
+public class AesEcbSingleBlockEncryptionTest {
+
+ private static final byte[] PLAINTEXT = base16().decode("F30F4E786C59A7BBF3873B5A49BA97EA");
+
+ @Test
+ public void encryptDecryptSuccessful() throws Exception {
+ byte[] secret = AesEcbSingleBlockEncryption.generateKey();
+ byte[] encrypted = AesEcbSingleBlockEncryption.encrypt(secret, PLAINTEXT);
+ assertThat(encrypted).isNotEqualTo(PLAINTEXT);
+ byte[] decrypted = AesEcbSingleBlockEncryption.decrypt(secret, encrypted);
+ assertThat(decrypted).isEqualTo(PLAINTEXT);
+ }
+
+ @Test(expected = IllegalArgumentException.class)
+ public void encryptionSizeLimitationEnforced() throws Exception {
+ byte[] secret = AesEcbSingleBlockEncryption.generateKey();
+ byte[] largePacket = Bytes.concat(PLAINTEXT, PLAINTEXT);
+ AesEcbSingleBlockEncryption.encrypt(secret, largePacket);
+ }
+
+ @Test(expected = IllegalArgumentException.class)
+ public void decryptionSizeLimitationEnforced() throws Exception {
+ byte[] secret = AesEcbSingleBlockEncryption.generateKey();
+ byte[] largePacket = Bytes.concat(PLAINTEXT, PLAINTEXT);
+ AesEcbSingleBlockEncryption.decrypt(secret, largePacket);
+ }
+}