Question

我正在研究AES算法，我有这个我无法解决的例外。

javax.crypto.BadPaddingException: Given final block not properly padded
at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
at com.sun.crypto.provider.AESCipher.engineDoFinal(DashoA13*..)
at javax.crypto.Cipher.doFinal(DashoA13*..)

解密部分发生异常。我在与解密算法

的不同位置初始化密钥

KeyGenerator kgen = KeyGenerator.getInstance("AES");//key generation for AES
kgen.init(128); // 192 and 256 bits may not be available

然后我将其从文件中读取的密文传递给以下方法

 public String decrypt(String message, SecretKey skey) {

    byte[] raw = skey.getEncoded();
    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
    // Instantiate the cipher
    Cipher cipher;

    byte[] original = null;
    try {
        cipher = Cipher.getInstance("AES");

        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
        System.out.println("Original string: "
                + message);
        original = cipher.doFinal(message.trim().getBytes());  //here where I got the exception
        String originalString = new String(original);
       }
 //catches

修改这是加密方法。

public String encrypt(String message, SecretKey skey) {
    byte[] raw = skey.getEncoded();
    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");

    // Instantiate the cipher

    Cipher cipher;
    byte[] encrypted = null;
    try {
        cipher = Cipher.getInstance("AES");

        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

        encrypted = cipher.doFinal(message.getBytes());
        System.out.println("raw is " + encrypted);

    } catches
    return asHex(encrypted);
}

这是asHex方法

  public static String asHex(byte buf[]) {
    StringBuffer strbuf = new StringBuffer(buf.length * 2);
    int i;

    for (i = 0; i < buf.length; i++) {
        if (((int) buf[i] & 0xff) < 0x10) {
            strbuf.append("0");
        }

        strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
    }

    return strbuf.toString();
}

这是我从文件

中读取密文的地方

static public String readFile(String filePath) {
    StringBuilder file = new StringBuilder();
    String line = null;
    try {
        FileReader reader = new FileReader(filePath);
        BufferedReader br = new BufferedReader(reader);
        if (br != null) {
            line = br.readLine();
            while (line != null) {
                file.append(line);
                //      System.out.println("line is " + line);
                line = br.readLine();

            }
        }
        br.close();
        reader.close();
    } catch (IOException ex) {
        Logger.getLogger(FileManagement.class.getName()).log(Level.SEVERE, null, ex);
    }
    System.out.println("line is " + file.toString());
    return String.valueOf(file);

}

有人可以帮忙吗？

Answer 1

好的，问题是您正在将加密的字节转换为十六进制字符串（使用asHex方法），但是没有正确地将十六进制字符串转换回字节数组以进行解密。您无法使用getBytes。

您可以使用以下method将十六进制字符串转换为字节数组：

public static byte[] fromHexString(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                             + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

然后更改您的解密方法：

original = cipher.doFinal(fromHexString(message));

Answer 2

我确实有一个Bad Padding Exception并且无法在互联网上找到我的问题的解决方案。自从我在一些艰苦的工作时间后发现它，我在这里给它。

我的问题是，我正在读取硬盘上的文件，并通过缓冲区加密，始终调用doFinal（）方法而不是update（）方法。所以在解密时，我有填充错误

    input = new FileInputStream(file);
    output = new FileOutputStream(newFile);

    Cipher cipher = Cipher.getInstance("DES");
    cipher.init(Cipher.ENCRYPT_MODE, mySecretKey);

    byte[] buf = new byte[1024];

    count = input.read(buf);
    while (count >= 0) {
        output.write(cipher.update(buf, 0, count)); // HERE I WAS DOING doFinal() method
        count = input.read(buf);
    }
    output.write(cipher.doFinal()); // AND I DID NOT HAD THIS LINE BEFORE
    output.flush();

使用相同的方法解密时，但使用带有DECRYPT_MODE的Cipher init

    input = new FileInputStream(file);
    output = new FileOutputStream(newFile);

    Cipher cipher = Cipher.getInstance("DES");
    cipher.init(Cipher.DECRYPT_MODE, mySecretKey);

    byte[] buf = new byte[1024];

    count = input.read(buf);

    while (count >= 0) {
        output.write(cipher.update(buf, 0, count)); // HERE I WAS DOING doFinal() method

        //AND HERE WAS THE BadPaddingExceotion -- the first pass in the while structure

        count = input.read(buf);
    }
    output.write(cipher.doFinal()); // AND I DID NOT HAD THIS LINE BEFORE
    output.flush();

编写代码后，我不再有任何BadPaddingException。

我可能确切地说，只有当原始清除文件长度（通过file.length（）获得）大于缓冲区时才会出现此异常。否则，我们不需要在while结构中多次传递，并且我们可以通过doFinal（）调用在一次传递中加密。这证明了在您尝试加密的文件大小之后的异常的随机特性。

我希望你读得好！

Answer 3

我猜表达式message.trim().getBytes()不会返回加密邮件时生成的相同字节。特别是trim()方法可以删除在加密消息中添加为填充的字节。

验证加密过程中返回的doFinal()方法数组和返回的message.trim().getBytes()数组：

获得相同的字节数（数组长度）
在数组中获得相同的字节

Answer 4

KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(512);
KeyPair rsaKeyPair = kpg.genKeyPair();
byte[] txt = "This is a secret message.".getBytes();
System.out.println("Original clear message: " + new String(txt));

// encrypt
Cipher cipher;
try
{
    cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
    cipher.init(Cipher.ENCRYPT_MODE, rsaKeyPair.getPublic());
    txt = cipher.doFinal(txt);
}
catch (Throwable e)
{
    e.printStackTrace();
    return;
}
System.out.println("Encrypted message: " + new String(txt));

// decrypt
try
{
    cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
    cipher.init(Cipher.DECRYPT_MODE, rsaKeyPair.getPrivate());
    txt = cipher.doFinal(txt);
}
catch (Throwable e)
{
    e.printStackTrace();
    return;
}
System.out.println("Decrypted message: " + new String(txt));

Answer 5

这是一个我可以使用带有RSA加密的jks密钥库拼凑起来的解决方案

import javax.crypto.Cipher;
import javax.xml.bind.DatatypeConverter;
import java.security.Key;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.KeyStore;
import java.security.cert.Certificate;

public class Main {

    public static void main(String[] args) {

        byte[] txt = "This is a secret message for your own eyes only".getBytes();
        byte[] encText;
        try{

            // Load the keystore
            KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
            char[] password = "keystorePassword".toCharArray();
            java.io.FileInputStream fis = new java.io.FileInputStream("/path/to/keystore/myKeyStore.jks");
            ks.load(fis, password);
            fis.close();

            Key rsakey = ks.getKey("mykeyalias", password);
            Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");

            // Encrypt
            Certificate cert = ks.getCertificate("mykeyalias");
            try
            {
                cipher.init(Cipher.ENCRYPT_MODE, cert.getPublicKey());
                encText = cipher.doFinal(txt);
                System.out.println(encText.toString());
            }
            catch (Throwable e)
            {
                e.printStackTrace();
                return;
            }

            // Decrypt
            cipher.init(Cipher.DECRYPT_MODE, rsakey);
            String decrypted = new String(cipher.doFinal(encText));
            System.out.println(decrypted);


        } catch (Exception e) {
            System.out.println("error" + e);
        }
}

javax.crypto.BadPaddingException

5 个答案: