我的前提是我可以使用 AndroidKeyStore 来保护任意数据块，并将它们称为“密钥”。但是，我越深入研究，就越清楚 KeyStore API 与安全相关的对象纠缠不清：证书、KeySpecs、提供程序等。它不是为存储任意数据而设计的，而且我看不到一个简单的将它弯曲到那个目的的路径。
但是，AndroidKeyStore 可用于帮助我保护敏感数据。我可以使用它来管理我将用来加密应用程序本地数据的加密密钥。通过结合使用 AndroidKeyStore、CipherOutputStream 和 CipherInputStream，我们可以：
- 在设备上生成、安全存储和检索加密密钥
- 加密任意数据并将其保存在设备上（在应用程序的目录中，将进一步受到文件系统权限的保护）
- 访问和解密数据以供后续使用。
这里是一些示例代码，演示了如何实现这一点。
try {
KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
keyStore.load(null);
String alias = "key3";
int nBefore = keyStore.size();
// Create the keys if necessary
if (!keyStore.containsAlias(alias)) {
Calendar notBefore = Calendar.getInstance();
Calendar notAfter = Calendar.getInstance();
notAfter.add(Calendar.YEAR, 1);
KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(this)
.setAlias(alias)
.setKeyType("RSA")
.setKeySize(2048)
.setSubject(new X500Principal("CN=test"))
.setSerialNumber(BigInteger.ONE)
.setStartDate(notBefore.getTime())
.setEndDate(notAfter.getTime())
.build();
KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
generator.initialize(spec);
KeyPair keyPair = generator.generateKeyPair();
}
int nAfter = keyStore.size();
Log.v(TAG, "Before = " + nBefore + " After = " + nAfter);
// Retrieve the keys
KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry)keyStore.getEntry(alias, null);
RSAPrivateKey privateKey = (RSAPrivateKey) privateKeyEntry.getPrivateKey();
RSAPublicKey publicKey = (RSAPublicKey) privateKeyEntry.getCertificate().getPublicKey();
Log.v(TAG, "private key = " + privateKey.toString());
Log.v(TAG, "public key = " + publicKey.toString());
// Encrypt the text
String plainText = "This text is supposed to be a secret!";
String dataDirectory = getApplicationInfo().dataDir;
String filesDirectory = getFilesDir().getAbsolutePath();
String encryptedDataFilePath = filesDirectory + File.separator + "keep_yer_secrets_here";
Log.v(TAG, "plainText = " + plainText);
Log.v(TAG, "dataDirectory = " + dataDirectory);
Log.v(TAG, "filesDirectory = " + filesDirectory);
Log.v(TAG, "encryptedDataFilePath = " + encryptedDataFilePath);
Cipher inCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
inCipher.init(Cipher.ENCRYPT_MODE, publicKey);
Cipher outCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
outCipher.init(Cipher.DECRYPT_MODE, privateKey);
CipherOutputStream cipherOutputStream =
new CipherOutputStream(
new FileOutputStream(encryptedDataFilePath), inCipher);
cipherOutputStream.write(plainText.getBytes("UTF-8"));
cipherOutputStream.close();
CipherInputStream cipherInputStream =
new CipherInputStream(new FileInputStream(encryptedDataFilePath),
outCipher);
byte [] roundTrippedBytes = new byte[1000]; // TODO: dynamically resize as we get more data
int index = 0;
int nextByte;
while ((nextByte = cipherInputStream.read()) != -1) {
roundTrippedBytes[index] = (byte)nextByte;
index++;
}
String roundTrippedString = new String(roundTrippedBytes, 0, index, "UTF-8");
Log.v(TAG, "round tripped string = " + roundTrippedString);
} catch (NoSuchAlgorithmException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (NoSuchProviderException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (InvalidAlgorithmParameterException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (KeyStoreException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (CertificateException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (IOException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (UnrecoverableEntryException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (NoSuchPaddingException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (InvalidKeyException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (BadPaddingException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (IllegalBlockSizeException e) {
Log.e(TAG, Log.getStackTraceString(e));
} catch (UnsupportedOperationException e) {
Log.e(TAG, Log.getStackTraceString(e));
}