在Android应用程序中存储凭据
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内容图文
我们如何安全地存储凭据数据以访问Android应用程序中的smtp服务器？这些数据是常量,只有开发人员才能知道.目前将它们存储在代码中,但这并不安全,因为可以通过反编译应用程序来查看它们.
是否可以为此目的使用Android Keystore System？如何使用？最重要的是,Android Keystore在植根设备上是否有效？
解决方法:
在android应用程序中,您可以将数据存储在SharedPreferences中,但由于此数据实际上存储在文件中,因此具有手机根权限的任何人都可以访问它.如果您要存储凭据或任何其他敏感数据,则意味着安全漏洞.
为了避免其他人看到纯文本格式的数据,一种解决方案是在存储数据之前对其进行加密. Android从API 18开始引入了KeyStore,它可以存储用于加密和解密数据的密钥.
在API 23之前的问题是您无法将AES密钥存储在KeyStore中,因此用于加密的最可靠的密钥是带有私钥和公钥的RSA.
所以我想出的解决方案是：
对于23以下的API
>您将生成RSA私钥和公钥,并将其保存在KeyStore中,生成AES密钥,使用RSA公钥对其进行加密,然后将其保存到SharedPreferences中.
>每次需要使用AES密钥将加密的数据保存在SharedPreferences中时,都会从SharedPreferences获得加密的AES密钥,使用RSA私钥对其进行解密,并使用已经解密的AES密钥对要保存到SharedPreferences的数据进行加密.
>要解密数据,过程几乎相同,从SharedPreferences获取加密的AES密钥,使用RSA私钥解密,从要解密的SharedPreferences获取加密的数据,然后使用解密的AES密钥解密.
适用于API 23以上
>只需生成一个AES密钥并将其存储在KeyStore中,并在需要进行数据加密/解密时随时访问它.
还添加了用于加密的生成的IV.
码：
public class KeyHelper{
private static final String RSA_MODE = "RSA/ECB/PKCS1Padding";
private static final String AES_MODE_M = "AES/GCM/NoPadding";
private static final String KEY_ALIAS = "KEY";
private static final String AndroidKeyStore = "AndroidKeyStore";
public static final String SHARED_PREFENCE_NAME = "SAVED_TO_SHARED";
public static final String ENCRYPTED_KEY = "ENCRYPTED_KEY";
public static final String PUBLIC_IV = "PUBLIC_IV";
private KeyStore keyStore;
private static KeyHelper keyHelper;
public static KeyHelper getInstance(Context ctx){
if(keyHelper == null){
try{
keyHelper = new KeyHelper(ctx);
} catch (NoSuchPaddingException | NoSuchProviderException | NoSuchAlgorithmException | InvalidAlgorithmParameterException | KeyStoreException | CertificateException | IOException e){
e.printStackTrace();
}
}
return keyHelper;
}
public KeyHelper(Context ctx) throws NoSuchPaddingException,NoSuchProviderException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, KeyStoreException, CertificateException, IOException {
this.generateEncryptKey(ctx);
this.generateRandomIV(ctx);
if(android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.M){
try{
this.generateAESKey(ctx);
} catch(Exception e){
e.printStackTrace();
}
}
}
private void generateEncryptKey(Context ctx) throws NoSuchProviderException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, KeyStoreException, CertificateException, IOException {
keyStore = KeyStore.getInstance(AndroidKeyStore);
keyStore.load(null);
if(android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M){
if (!keyStore.containsAlias(KEY_ALIAS)) {
KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, AndroidKeyStore);
keyGenerator.init(
new KeyGenParameterSpec.Builder(KEY_ALIAS,
KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
.setBlockModes(KeyProperties.BLOCK_MODE_GCM)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
.setRandomizedEncryptionRequired(false)
.build());
keyGenerator.generateKey();
}
} else{
if (!keyStore.containsAlias(KEY_ALIAS)) {
// Generate a key pair for encryption
Calendar start = Calendar.getInstance();
Calendar end = Calendar.getInstance();
end.add(Calendar.YEAR, 30);
KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(ctx)
.setAlias(KEY_ALIAS)
.setSubject(new X500Principal("CN=" + KEY_ALIAS))
.setSerialNumber(BigInteger.TEN)
.setStartDate(start.getTime())
.setEndDate(end.getTime())
.build();
KeyPairGenerator kpg = KeyPairGenerator.getInstance(KeyProperties.KEY_ALGORITHM_RSA, AndroidKeyStore);
kpg.initialize(spec);
kpg.generateKeyPair();
}
}
}
private byte[] rsaEncrypt(byte[] secret) throws Exception{
KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry) keyStore.getEntry(KEY_ALIAS, null);
// Encrypt the text
Cipher inputCipher = Cipher.getInstance(RSA_MODE, "AndroidOpenSSL");
inputCipher.init(Cipher.ENCRYPT_MODE, privateKeyEntry.getCertificate().getPublicKey());
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
CipherOutputStream cipherOutputStream = new CipherOutputStream(outputStream, inputCipher);
cipherOutputStream.write(secret);
cipherOutputStream.close();
return outputStream.toByteArray();
}
private byte[] rsaDecrypt(byte[] encrypted) throws Exception {
KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry)keyStore.getEntry(KEY_ALIAS, null);
Cipher output = Cipher.getInstance(RSA_MODE, "AndroidOpenSSL");
output.init(Cipher.DECRYPT_MODE, privateKeyEntry.getPrivateKey());
CipherInputStream cipherInputStream = new CipherInputStream(
new ByteArrayInputStream(encrypted), output);
ArrayList<Byte> values = new ArrayList<>();
int nextByte;
while ((nextByte = cipherInputStream.read()) != -1) {
values.add((byte)nextByte);
}
byte[] bytes = new byte[values.size()];
for(int i = 0; i < bytes.length; i++) {
bytes[i] = values.get(i).byteValue();
}
return bytes;
}
private void generateAESKey(Context context) throws Exception{
SharedPreferences pref = context.getSharedPreferences(SHARED_PREFENCE_NAME, Context.MODE_PRIVATE);
String enryptedKeyB64 = pref.getString(ENCRYPTED_KEY, null);
if (enryptedKeyB64 == null) {
byte[] key = new byte[16];
SecureRandom secureRandom = new SecureRandom();
secureRandom.nextBytes(key);
byte[] encryptedKey = rsaEncrypt(key);
enryptedKeyB64 = Base64.encodeToString(encryptedKey, Base64.DEFAULT);
SharedPreferences.Editor edit = pref.edit();
edit.putString(ENCRYPTED_KEY, enryptedKeyB64);
edit.apply();
}
}
private Key getAESKeyFromKS() throws NoSuchProviderException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, KeyStoreException, CertificateException, IOException, UnrecoverableKeyException{
keyStore = KeyStore.getInstance(AndroidKeyStore);
keyStore.load(null);
SecretKey key = (SecretKey)keyStore.getKey(KEY_ALIAS,null);
return key;
}
private Key getSecretKey(Context context) throws Exception{
SharedPreferences pref = context.getSharedPreferences(SHARED_PREFENCE_NAME, Context.MODE_PRIVATE);
String enryptedKeyB64 = pref.getString(ENCRYPTED_KEY, null);
byte[] encryptedKey = Base64.decode(enryptedKeyB64, Base64.DEFAULT);
byte[] key = rsaDecrypt(encryptedKey);
return new SecretKeySpec(key, "AES");
}
public String encrypt(Context context, String input) throws NoSuchAlgorithmException, NoSuchPaddingException, NoSuchProviderException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException {
Cipher c;
SharedPreferences pref = context.getSharedPreferences(SHARED_PREFENCE_NAME, Context.MODE_PRIVATE);
String publicIV = pref.getString(PUBLIC_IV, null);
if(android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M){
c = Cipher.getInstance(AES_MODE_M);
try{
c.init(Cipher.ENCRYPT_MODE, getAESKeyFromKS(), new GCMParameterSpec(128,Base64.decode(publicIV, Base64.DEFAULT)));
} catch(Exception e){
e.printStackTrace();
}
} else{
c = Cipher.getInstance(AES_MODE_M);
try{
c.init(Cipher.ENCRYPT_MODE, getSecretKey(context),new GCMParameterSpec(128,Base64.decode(publicIV, Base64.DEFAULT)));
} catch (Exception e){
e.printStackTrace();
}
}
byte[] encodedBytes = c.doFinal(input.getBytes("UTF-8"));
return Base64.encodeToString(encodedBytes, Base64.DEFAULT);
}
public String decrypt(Context context, String encrypted) throws NoSuchAlgorithmException, NoSuchPaddingException, NoSuchProviderException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException {
Cipher c;
SharedPreferences pref = context.getSharedPreferences(SHARED_PREFENCE_NAME, Context.MODE_PRIVATE);
String publicIV = pref.getString(PUBLIC_IV, null);
if(android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M){
c = Cipher.getInstance(AES_MODE_M);
try{
c.init(Cipher.DECRYPT_MODE, getAESKeyFromKS(), new GCMParameterSpec(128,Base64.decode(publicIV, Base64.DEFAULT)));
} catch(Exception e){
e.printStackTrace();
}
} else{
c = Cipher.getInstance(AES_MODE_M);
try{
c.init(Cipher.DECRYPT_MODE, getSecretKey(context), new GCMParameterSpec(128,Base64.decode(publicIV, Base64.DEFAULT)));
} catch (Exception e){
e.printStackTrace();
}
}
byte[] decodedValue = Base64.decode(encrypted.getBytes("UTF-8"), Base64.DEFAULT);
byte[] decryptedVal = c.doFinal(decodedValue);
return new String(decryptedVal);
}
public void generateRandomIV(Context ctx){
SharedPreferences pref = ctx.getSharedPreferences(SHARED_PREFENCE_NAME, Context.MODE_PRIVATE);
String publicIV = pref.getString(PUBLIC_IV, null);
if(publicIV == null){
SecureRandom random = new SecureRandom();
byte[] generated = random.generateSeed(12);
String generatedIVstr = Base64.encodeToString(generated, Base64.DEFAULT);
SharedPreferences.Editor edit = pref.edit();
edit.putString(PUBLIC_IV_PERSONAL, generatedIVstr);
edit.apply();
}
}
private String getStringFromSharedPrefs(String key, Context ctx){
SharedPreferences prefs = ctx.getSharedPreferences(MyConstants.APP_SHAREDPREFS, 0);
return prefs.getString(key, null);
}
}
注意：这仅适用于API 18及更高版本
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