java - 对字符串字节执行 RSA 时出现 IllegalBlockSize 异常

Question

我正在尝试用 Java 为服务器编写 RSA 加密和解密类，客户端将在服务器上来回传递字符串。我有以下类代码:

public class RSAEncryption {
public static final String KEYGENALGORITHM = "RSA";
public static final String ALGORITHM = "RSA/ECB/PKCS1Padding";

public static KeyPairContainer generateKey() {
      KeyPairGenerator keyGen;
      KeyPair key;
    try {
        keyGen = KeyPairGenerator.getInstance(KEYGENALGORITHM);
        keyGen.initialize(1024);
        key = keyGen.generateKeyPair();
        return new KeyPairContainer(key.getPublic(), key.getPrivate());
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
        System.out.println("Error: No such algorithm");
    }
    return null;
 }

public static String pubkeyToString(PublicKey key){
    byte[] array = key.getEncoded();
    BASE64Encoder encoder = new BASE64Encoder();
    String tempstring = encoder.encode(array);
    return tempstring;
}

public static PublicKey stringToPubKey(String string){
    BASE64Decoder decoder = new BASE64Decoder();
    try {
        byte[] array = decoder.decodeBuffer(string);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(array);
        KeyFactory keyFact = KeyFactory.getInstance(KEYGENALGORITHM);
        PublicKey pubKey = keyFact.generatePublic(x509KeySpec);
        return pubKey;
    } catch (IOException | NoSuchAlgorithmException | InvalidKeySpecException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } return null;
}

public static byte[] rSAencrypt(byte[] plaintext, String keystring) {
    Cipher cipher;
    try {
        PublicKey key = stringToPubKey(keystring);
        cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, key);
        byte[] cipherText = cipher.doFinal(plaintext);
        //String cipherText = new String(cipherTextbytes);
        return cipherText;
    } catch (NoSuchAlgorithmException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (NoSuchPaddingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (InvalidKeyException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IllegalBlockSizeException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (BadPaddingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return null;

}

public static byte[] rSAdecrypt(byte[] ciphertext, PrivateKey key){
    Cipher cipher;
    try {
        //byte[] ciphertext = ciphertextstring.getBytes();
        cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, key);
        byte[] decryptedText = cipher.doFinal(ciphertext);
        return decryptedText;
    } catch (NoSuchAlgorithmException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (NoSuchPaddingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (InvalidKeyException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IllegalBlockSizeException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (BadPaddingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return null;
}
}

我有以下测试类代码:

public class RSAEncryptionKeyDemo {
public static void main(String[] args){
    KeyPairContainer keyPair = RSAEncryption.generateKey();
    PublicKey pubKey = keyPair.getPublicKey();
    String pubKeytext = RSAEncryption.pubkeyToString(pubKey);
    System.out.println(pubKeytext);

    String plaintext = "Hello world!";
    byte[] ciphertext = RSAEncryption.rSAencrypt(plaintext.getBytes(), pubKeytext);
    String ciphertextString = new String(ciphertext);
    System.out.println(ciphertextString);

    PrivateKey privkey = keyPair.getPrivateKey();
    byte[] decryptedText = RSAEncryption.rSAdecrypt(ciphertextString.getBytes(), privkey);

    String decryptedTextstring = new String(decryptedText);

    System.out.println(decryptedTextstring);


}
}

但是，当我尝试运行测试类时， key 生成和加密工作正常，但当我尝试解密时会抛出错误。错误是javax.crypto.IllegalBlockSizeException:数据不能长于128字节，但是我的数据肯定小于128字节。

我可以确认将公钥转换为字符串并返回会返回相同的公钥。我也尝试过仅使用字节来测试代码，效果很好。该错误显然是在尝试解密从字符串中获取的字节时发生的。

是否有某种方法可以解密从字符串中获取的字节而不引发此错误？预先感谢，非常感谢。

编辑:我想我可能已经隔离了这个问题。我试图将加密的字节数组转换为字符串，然后从中提取字节，但是加密的字节数组无论如何都无法正确转换为字符串，因此当我获取字节时，它不会提取原始加密字节数组的内容。这是正确的吗？如果是，我如何正确地将字节数组转换为字符串以便我们可以交换它？

Answer 1

如果你这样做

byte[] ciphertext = RSAEncryption.rSAencrypt(plaintext.getBytes(), pubKeytext);
//String ciphertextString = new String(ciphertext);
//System.out.println(ciphertextString);

PrivateKey privkey = keyPair.getPrivateKey();
byte[] decryptedText = RSAEncryption.rSAdecrypt(ciphertext, privkey);

代码运行得很好。您无法将字节数组转换为字符串，因为字节会转换为字符并返回字节(使用 getBytes()) - 取决于您的默认字符集。 new String(ciphertext) 删除不可打印的字符，从而更改密文，从而使明文无法恢复。 (感谢 Artjom B. 指出了这一点。)

只需使用 Base64 或二进制来传输您的密文，例如:

byte[] ciphertext = RSAEncryption.rSAencrypt(plaintext.getBytes(), pubKeytext);
String ciphertextString = Base64.toBase64String(ciphertext);
System.out.println(ciphertextString);

PrivateKey privkey = keyPair.getPrivateKey();
byte[] decryptedText = RSAEncryption.rSAdecrypt(Base64.decode(ciphertextString), privkey);

(我在这里使用 BouncyCaSTLe Base64 编码器。)