OWASP 类别：MASVS-CRYPTO：加密
概览
开发者会利用加密技术，通过可靠的算法保护数据的机密性和完整性。然而密钥存储的使用偏少，并且通常通过代码或资源文件（如 strings.xml）以字符串或字节数组的形式硬编码到应用中。如果在应用的任何文件中公开 Secret，就会违反 Kerchoff 的原则，并且安全模型可能会被视为已损坏。
影响
掌握逆向工程工具的攻击者可以非常轻松地检索硬编码的 Secret。具体影响可能会因情况而异，但在很多情况下，此漏洞可能会导致重大的安全问题，例如对敏感数据的不当访问。
缓解措施
您可以通过以下方法缓解此问题：如果您希望采用系统级凭据，可考虑使用 KeyChain API；如果您想让单个应用可以存储自己的凭据，并且只有该应用本身可以访问相应凭据，可使用 Android 密钥库提供程序。
以下代码段展示了如何利用 KeyStore 存储和使用对称密钥：
Kotlin
private val ANDROID_KEY_STORE_PROVIDER = "AndroidKeyStore"
private val ANDROID_KEY_STORE_ALIAS = "AES_KEY_DEMO"
@Throws(
KeyStoreException::class,
NoSuchAlgorithmException::class,
NoSuchProviderException::class,
InvalidAlgorithmParameterException::class
)
private fun createAndStoreSecretKey() {
val builder: KeyGenParameterSpec.Builder = KeyGenParameterSpec.Builder(
ANDROID_KEY_STORE_ALIAS,
KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT
)
val keySpec: KeyGenParameterSpec = builder
.setKeySize(256)
.setBlockModes(KeyProperties.BLOCK_MODE_GCM)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
.setRandomizedEncryptionRequired(true)
.build()
val aesKeyGenerator: KeyGenerator =
KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, ANDROID_KEY_STORE_PROVIDER)
aesKeyGenerator.init(keySpec)
val key: SecretKey = aesKeyGenerator.generateKey()
}
@Throws(
KeyStoreException::class,
UnrecoverableEntryException::class,
NoSuchAlgorithmException::class,
CertificateException::class,
IOException::class,
NoSuchPaddingException::class,
InvalidKeyException::class,
IllegalBlockSizeException::class,
BadPaddingException::class
)
private fun encryptWithKeyStore(plainText: String): ByteArray? {
// Initialize KeyStore
val keyStore: KeyStore = KeyStore.getInstance(ANDROID_KEY_STORE_PROVIDER)
keyStore.load(null)
// Retrieve the key with alias androidKeyStoreAlias created before
val keyEntry: KeyStore.SecretKeyEntry =
keyStore.getEntry(ANDROID_KEY_STORE_ALIAS, null) as KeyStore.SecretKeyEntry
val key: SecretKey = keyEntry.secretKey
// Use the secret key at your convenience
val cipher: Cipher = Cipher.getInstance("AES/GCM/NoPadding")
cipher.init(Cipher.ENCRYPT_MODE, key)
return cipher.doFinal(plainText.toByteArray())
}
Java
static private final String ANDROID_KEY_STORE_PROVIDER = "AndroidKeyStore";
static private final String ANDROID_KEY_STORE_ALIAS = "AES_KEY_DEMO";
private void createAndStoreSecretKey() throws KeyStoreException, NoSuchAlgorithmException, NoSuchProviderException, InvalidAlgorithmParameterException {
KeyGenParameterSpec.Builder builder = new KeyGenParameterSpec.Builder(
ANDROID_KEY_STORE_ALIAS,
KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT);
KeyGenParameterSpec keySpec = builder
.setKeySize(256)
.setBlockModes(KeyProperties.BLOCK_MODE_GCM)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
.setRandomizedEncryptionRequired(true)
.build();
KeyGenerator aesKeyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, ANDROID_KEY_STORE_PROVIDER);
aesKeyGenerator.init(keySpec);
SecretKey key = aesKeyGenerator.generateKey();
}
private byte[] encryptWithKeyStore(final String plainText) throws KeyStoreException, UnrecoverableEntryException, NoSuchAlgorithmException, CertificateException, IOException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
// Initialize KeyStore
KeyStore keyStore = KeyStore.getInstance(ANDROID_KEY_STORE_PROVIDER);
keyStore.load(null);
// Retrieve the key with alias ANDROID_KEY_STORE_ALIAS created before
KeyStore.SecretKeyEntry keyEntry = (KeyStore.SecretKeyEntry) keyStore.getEntry(ANDROID_KEY_STORE_ALIAS, null);
SecretKey key = keyEntry.getSecretKey();
// Use the secret key at your convenience
final Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
cipher.init(Cipher.ENCRYPT_MODE, key);
return cipher.doFinal(plainText.getBytes());
}