Add a CipherManager for en/decryption using AndroidCrypto

CipherManager can be used to exchange the Android version with the
remote device.

Bug: 253307662

Test: Manually tested encrypt() then descrypt() and checked the output
string matches the original string

Change-Id: I08efe8fa831ddae3fd5adb11b82c3b8803d1f4e5

services/companion/java/com/android/server/companion/transport/CryptoManager.java

@@ -0,0 +1,143 @@
+/*
+ * Copyright (C) 2023 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.companion.transport;
+
+import android.security.keystore.KeyGenParameterSpec;
+import android.security.keystore.KeyProperties;
+import android.util.Slog;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.KeyStore;
+import java.security.KeyStoreException;
+import java.security.NoSuchAlgorithmException;
+import java.security.UnrecoverableEntryException;
+import java.security.cert.CertificateException;
+
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.KeyGenerator;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.SecretKey;
+import javax.crypto.spec.IvParameterSpec;
+
+/**
+ * This class can be used to encrypt and decrypt bytes using Android Cryptography
+ */
+public class CryptoManager {
+
+    private static final String TAG = "CDM_CryptoManager";
+
+    private static final String KEY_STORE_ALIAS = "cdm_secret";
+    private static final String ALGORITHM = KeyProperties.KEY_ALGORITHM_AES;
+    private static final String BLOCK_MODE = KeyProperties.BLOCK_MODE_CBC;
+    private static final String PADDING = KeyProperties.ENCRYPTION_PADDING_PKCS7;
+    private static final String TRANSFORMATION = ALGORITHM + "/" + BLOCK_MODE + "/" + PADDING;
+
+    private final KeyStore mKeyStore;
+
+    public CryptoManager() {
+        // Initialize KeyStore
+        try {
+            mKeyStore = KeyStore.getInstance("AndroidKeyStore");
+            mKeyStore.load(null);
+        } catch (KeyStoreException | IOException | NoSuchAlgorithmException
+                 | CertificateException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * Output format: | iv length (int) | iv | encrypted bytes length (int) | encrypted bytes |
+     */
+    public byte[] encrypt(byte[] input) {
+        try {
+            // Encrypt using Cipher
+            Cipher encryptCipher = Cipher.getInstance(TRANSFORMATION);
+            encryptCipher.init(Cipher.ENCRYPT_MODE, getKey());
+            byte[] encryptedBytes = encryptCipher.doFinal(input);
+
+            // Write to bytes
+            ByteBuffer buffer = ByteBuffer.allocate(
+                            4 + encryptCipher.getIV().length + 4 + encryptedBytes.length)
+                    .putInt(encryptCipher.getIV().length)
+                    .put(encryptCipher.getIV())
+                    .putInt(encryptedBytes.length)
+                    .put(encryptedBytes);
+            return buffer.array();
+        } catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException
+                 | IllegalBlockSizeException | BadPaddingException e) {
+            Slog.e(TAG, e.getMessage());
+            return null;
+        }
+    }
+
+    /**
+     * Input format: | iv length (int) | iv | encrypted bytes length (int) | encrypted bytes |
+     */
+    public byte[] decrypt(byte[] input) {
+        ByteBuffer buffer = ByteBuffer.wrap(input);
+        byte[] iv = new byte[buffer.getInt()];
+        buffer.get(iv);
+        byte[] encryptedBytes = new byte[buffer.getInt()];
+        buffer.get(encryptedBytes);
+        try {
+            Cipher decryptCipher = Cipher.getInstance(TRANSFORMATION);
+            decryptCipher.init(Cipher.DECRYPT_MODE, getKey(), new IvParameterSpec(iv));
+            return decryptCipher.doFinal(encryptedBytes);
+        } catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException
+                 | InvalidAlgorithmParameterException | IllegalBlockSizeException
+                 | BadPaddingException e) {
+            Slog.e(TAG, e.getMessage());
+            return null;
+        }
+    }
+
+    private SecretKey getKey() {
+        try {
+            KeyStore.Entry keyEntry = mKeyStore.getEntry(KEY_STORE_ALIAS, null);
+            if (keyEntry instanceof KeyStore.SecretKeyEntry
+                    && ((KeyStore.SecretKeyEntry) keyEntry).getSecretKey() != null) {
+                return ((KeyStore.SecretKeyEntry) keyEntry).getSecretKey();
+            } else {
+                return createKey();
+            }
+        } catch (NoSuchAlgorithmException | UnrecoverableEntryException | KeyStoreException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private SecretKey createKey() {
+        try {
+            KeyGenerator keyGenerator = KeyGenerator.getInstance(ALGORITHM);
+            keyGenerator.init(
+                    new KeyGenParameterSpec.Builder(KEY_STORE_ALIAS,
+                            KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
+                            .setBlockModes(BLOCK_MODE)
+                            .setEncryptionPaddings(PADDING)
+                            .setUserAuthenticationRequired(false)
+                            .setRandomizedEncryptionRequired(true)
+                            .build());
+            return keyGenerator.generateKey();
+        } catch (NoSuchAlgorithmException | InvalidAlgorithmParameterException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}