在Android设备上加密文件的关键在于不要存储密钥。为此,您已经添加了一个限制条件,即加密图片不需要密码。最后,由于非对称加密很慢,您需要使用AES来完成重量级工作。
这适用于RSA或任何其他非对称算法。
初始运行
1. 第一次运行时,生成密钥对并要求用户输入密码。
2. 将公钥以明文形式存储。使用从密码生成的AES密钥加密私钥。
加密
5. 为每个图片生成一个不同的AES密钥,并使用它来加密图像。使用公钥加密AES密钥,然后将其与图片一起存储。
解密
6. 要求用户输入密码。从中生成第一个AES密钥。使用它来解密私钥。使用私钥解密此图像的AES密钥。使用AES密钥解密文件并显示它。
(实际上我们有4个密钥。我们需要密钥对才能允许我们无需密码进行加密。我们需要第一个AES密钥来安全地存储私钥。我们需要第二个和可变的AES密钥来加密文件。)
我认为这应该是安全的,除了诸如键盘记录之类的攻击。Java代码应该非常简单明了。希望这很清楚。
完整示例使用AES和RSA。对于Curve,请仅更改RSA代码,尽管它不支持开箱即用,因此您需要外部库。此外,为了节省时间和简洁起见,代码比应该更安全。例如,我使用了ECB而不是CBC。
package il.co.falk;
import javax.crypto.*;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.*;
import java.security.spec.KeySpec;
import java.security.spec.PKCS8EncodedKeySpec;
public class SecureFile {
private PublicKey publicKey;
private byte[] privateKeyArray;
private byte[] salt = {1,2,3,4,5,6,7,8};
public static void main(String[] args) {
String password = "PASSWORD";
SecureFile secureFile = new SecureFile(password);
secureFile.test();
}
public void test() {
String password = "PASSWORD";
String imageFile = "348756348975634897562398479623896";
ImageAndKey imageAndKey = encryptImage(imageFile.getBytes());
byte[] decryptedImage = decryptImage(imageAndKey, password);
System.out.println(new String(imageFile));
System.out.println(new String(decryptedImage));
}
public SecureFile(String password) {
try {
generateRSAKeys(password);
} catch (Exception e) {
e.printStackTrace();
}
}
public ImageAndKey encryptImage(byte[] imageBytes) {
try {
byte[] secretKeyBytes = generateAESKey();
byte[] encryptedFile = aesEncrypt(imageBytes, secretKeyBytes);
byte[] encryptedKey = rsaEncrypt(secretKeyBytes);
return new ImageAndKey(encryptedFile, encryptedKey);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
public byte[] decryptImage(ImageAndKey imageAndKey, String password) {
try {
byte[] secretKeyBytes = generateAESKey(password);
byte[] decryptedPrivateKey = aesDecrypt(privateKeyArray, secretKeyBytes);
byte[] decryptedKey = rsaDecrypt(imageAndKey.aesKey, decryptedPrivateKey);
SecretKey secretKey = new SecretKeySpec(decryptedKey, "AES");
secretKeyBytes = secretKey.getEncoded();
byte[] decryptedBytes = aesDecrypt(imageAndKey.imageBytes, secretKeyBytes);
return decryptedBytes;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
private void generateRSAKeys(String password) throws Exception {
final KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
keyGen.initialize(512);
final KeyPair keyPair = keyGen.generateKeyPair();
publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();
byte[] secretKeyBytes = generateAESKey(password);
byte[] privateKeyBytes = privateKey.getEncoded();
privateKeyArray = aesEncrypt(privateKeyBytes, secretKeyBytes);
}
public byte[] rsaEncrypt(byte[] plainText) throws Exception {
final Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] cipherText = cipher.doFinal(plainText);
return cipherText;
}
public byte[] rsaDecrypt(byte[] cipherText, byte[] decryptedPrivateKeyArray) throws Exception {
PrivateKey privateKey = KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(decryptedPrivateKeyArray));
final Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] plainText = cipher.doFinal(cipherText);
return plainText;
}
private byte[] aesEncrypt(byte[] plainText, byte[] secretKeyBytes) throws Exception {
Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, getSecretKey(secretKeyBytes));
byte[] cipherText = cipher.doFinal(plainText);
return cipherText;
}
public byte[] aesDecrypt(byte[] cipherText, byte[] secretKeyBytes) throws Exception {
Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, getSecretKey(secretKeyBytes));
byte[] plainText = cipher.doFinal(cipherText);
return plainText;
}
private byte[] generateAESKey() throws Exception {
KeyGenerator keyGen = KeyGenerator.getInstance("AES");
keyGen.init(256);
SecretKey secretKey = keyGen.generateKey();
return secretKey.getEncoded();
}
private byte[] generateAESKey(String password) throws Exception {
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec spec = new PBEKeySpec(password.toCharArray(), salt, 65536, 256);
SecretKey tmp = factory.generateSecret(spec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
return secret.getEncoded();
}
private SecretKey getSecretKey(byte[] secretKeyBytes) throws Exception {
SecretKey secretKey = new SecretKeySpec(secretKeyBytes, "AES");
return secretKey;
}
class ImageAndKey {
public byte[] imageBytes;
public byte[] aesKey;
public ImageAndKey(byte[] imageBytes, byte[] aesKey) {
this.imageBytes = imageBytes;
this.aesKey = aesKey;
}
}
}