在Android中使用AES方法解密文件

Question

我在php中用AES加密法加密了文件，代码如下。

$ALGORITHM = 'AES-128-CBC';
$IV = '12dasdq3g5b2434b';
$password = '123';
openssl_encrypt($contenuto, $ALGORITHM, $password, 0, $IV);

现在我正在尝试在Android中解密它，但我总是面临InvalidKey异常：密钥长度不是128/192/256位错误。这是Android代码：

String initializationVector = "12dasdq3g5b2434b";
String password = "123";
FileInputStream fis = new FileInputStream(cryptFilepath);
FileOutputStream fos = new FileOutputStream(outputFilePath);
byte[] key = (password).getBytes("UTF-8");
MessageDigest sha = MessageDigest.getInstance("SHA-1");
key = sha.digest(key);
key = Arrays.copyOf(key,16);
SecretKeySpec sks = new SecretKeySpec(key, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, sks, new IvParameterSpec(initializationVector.getBytes()));
CipherInputStream cis = new CipherInputStream(fis, cipher);
int b;
byte[] d = new byte[16];
while((b = cis.read(d)) != -1) {
fos.write(d, 0, b);
}
fos.flush();
fos.close();
cis.close();

有人能建议我怎么做吗？任何帮助都将不胜感激。

Answer 1

在迈克尔的回答的帮助下，我写下了成功解密文件的代码。

在应用级别build.gradle文件中添加以下依赖项：

implementation 'commons-io:commons-io:2.7'
implementation 'commons-codec:commons-codec:1.13'

Java代码:

public static void decrypt(String path, String outPath) throws Exception {
    String password = "123";
    String initializationVector = "12dasdq3g5b2434b";
    byte[] key = new byte[16]; // 16 bytes for aes cbc 128
    System.arraycopy(password.getBytes(StandardCharsets.UTF_8), 0, key, 0, password.getBytes(StandardCharsets.UTF_8).length);
    SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
    IvParameterSpec ivParameterSpec = new IvParameterSpec(initializationVector.getBytes(StandardCharsets.UTF_8));

    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);

    byte[] input_file;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        input_file = Files.readAllBytes(Paths.get(path));
    } else {
        input_file = org.apache.commons.io.FileUtils.readFileToByteArray(new File(path));
    }

    byte[] decodedBytes;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        decodedBytes = Base64.getDecoder().decode(input_file);
    } else {
        decodedBytes = org.apache.commons.codec.binary.Base64.decodeBase64(input_file);
    }

    byte[] decryptedtext = cipher.doFinal(decodedBytes);
    FileOutputStream fos = new FileOutputStream(outPath);
    fos.write(decryptedtext);
    fos.flush();
    fos.close();
}

我希望这会有所帮助。

Answer 2

以下完整的工作示例展示了如何处理密码问题和进行Base64解码，这些示例只处理字符串而不是文件。请记住@Topaco所说的openssl以Base64编码输出，需要转换为字节格式，然后文件才能与CipherInputStream一起用于解密！

第三点（不是真正的错误）是，在Java/Android端，您不需要为字符串到字节数组的转换设置字符集，只需添加StandardCharset即可。UTF_8和你对这一点很满意。

当心没有适当的异常处理！

这是我的PHP代码示例:

<?php
// https://stackoverflow.com/questions/63113746/decrypt-file-using-aes-method-in-android
$ALGORITHM = 'AES-128-CBC';
$IV = '12dasdq3g5b2434b';
$password = '123';
$plaintext = "my content to encrypt";
echo 'plaintext: ' . $plaintext . PHP_EOL;
$ciphertext = openssl_encrypt($plaintext, $ALGORITHM, $password, 0, $IV);
echo 'ciphertext: ' . $ciphertext . PHP_EOL;
$decryptedtext = openssl_decrypt($ciphertext, $ALGORITHM, $password, 0, $IV);
echo 'decryptedtext: ' . $decryptedtext . PHP_EOL;
?>

PHP端的输出:

plaintext: my content to encrypt
ciphertext: DElx3eON2WX0MCj2GS8MnD+kn5NOu1i5IOTcrpKegG4=
decryptedtext: my content to encrypt

样本Java代码:

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

public class DecryptInJava {
    public static void main(String[] args) throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
        System.out.println("https://stackoverflow.com/questions/63113746/decrypt-file-using-aes-method-in-android");
        String password = "123";
        String initializationVector = "12dasdq3g5b2434b";
        String ciphertext = "DElx3eON2WX0MCj2GS8MnD+kn5NOu1i5IOTcrpKegG4="; // password 123 in openssl
        // openssl encodes the output in base64 encoding, so first we have to decode it
        byte[] ciphertextByte = Base64.getDecoder().decode(ciphertext);
        // creating a key filled with 16 'x0'
        byte[] key = new byte[16]; // 16 bytes for aes cbc 128
        // copying the password to the key, leaving the x0 at the end
        System.arraycopy(password.getBytes(StandardCharsets.UTF_8), 0, key, 0, password.getBytes(StandardCharsets.UTF_8).length);
        SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
        IvParameterSpec ivParameterSpec = new IvParameterSpec(initializationVector.getBytes(StandardCharsets.UTF_8));
        // don't use just AES because that defaults to AES/ECB...
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);
        byte[] decryptedtext = cipher.doFinal(ciphertextByte);
        System.out.println("decryptedtext: " + new String(decryptedtext));
    }
}

Java端的输出:

decryptedtext: my content to encrypt

Answer 3

问题中发布的原始代码使用流来读取、解密和写入相应的文件。这样就可以处理大于可用内存的文件。

然而，最初发布的代码缺少Base64解码，这是必要的，因为PHP代码的密文是Base64编码的。

使用Apache Commons编解码器的< code>Base64InputStream类可以轻松实现Base64解码，该类在< code>FileInputStream和< code>CipherInputStream之间运行，因此易于集成:

import org.apache.commons.codec.binary.Base64InputStream;

...

public static void decrypt(String ciphertextFilepath, String decryptedFilePath) throws Exception {
    
    String password = "123";
    String initializationVector = "12dasdq3g5b2434b";

    byte[] key = new byte[16];
    byte[] passwordBytes = password.getBytes(StandardCharsets.UTF_8);
    System.arraycopy(passwordBytes, 0, key, 0, passwordBytes.length);
    SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
    IvParameterSpec ivParameterSpec = new IvParameterSpec(initializationVector.getBytes(StandardCharsets.UTF_8));
    
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);
    
    try (FileInputStream fis = new FileInputStream(ciphertextFilepath);
         Base64InputStream b64is = new Base64InputStream(fis);
         CipherInputStream cis = new CipherInputStream(b64is, cipher);
         FileOutputStream fos = new FileOutputStream(decryptedFilePath)) {
            
        int read;
        byte[] buffer = new byte[16]; // 16 bytes for testing, in practice use a suitable size (depending on your RAM size), e.g. 64 Mi
        while((read = cis.read(buffer)) != -1) {
            fos.write(buffer, 0, read);
        }
    }
}

其他修复的错误/优化点是（另请参阅其他答案/评论）：

• 使用类似于PHP代码的CBC模式
• 使用PHP代码中的密钥
• 使用的编码的显式规范

编辑：考虑IV，参见@Michael Fehr的评论。

通常为每次加密生成新的随机IV。IV不是秘密的，通常放在密文之前，结果是Base64编码。接受者可以将两部分分开，因为静脉注射的大小是已知的（对应于块大小）。此构造还可以与Base64InputStream类结合使用，其中IV必须在Base64InputStream实例化和

...
try (FileInputStream fis = new FileInputStream(ciphertextFilepath);
     Base64InputStream b64is = new Base64InputStream(fis)){
        
    byte[] iv = b64is.readNBytes(16); // 16 bytes for AES
    IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
    
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);
            
    try (CipherInputStream cis = new CipherInputStream(b64is, cipher);
         FileOutputStream fos = new FileOutputStream(decryptedFilePath)) {
        ...

如果在加密过程中IV和密文分别进行Base64编码，然后连接，用分隔符分隔（参见@Michael Fehr的评论），则IV的确定必须在FileInpuStream和Base64InpuStream实例化之间完成（分隔符也必须刷新）。