java - 解密加密消息摘要时出现非法 block 大小异常

Question

我想解密加密的消息摘要。我的java程序中有这段代码:

 String bobSignedMsg = SignedMsg;

    //At the receiving end, Bob extracts the msg 
    // length, the msg text, and the digital
    // signature from the signed msg.
    //Get the message length.
    int MsgLen = Integer.parseInt(bobSignedMsg.trim().substring(bobSignedMsg.length()-6));
    System.out.println(
               "\n12. Bob's calculated msg len: "
                                 + MsgLen);

    //Get the message text.
    String bobMsgText = bobSignedMsg.substring(
                                 0,MsgLen);
    System.out.println(
               "\n13. Bob's extracted msg text: "
                             + bobMsgText);

    //Bob knows that everything following the msg
    // text except for the four characters at the
    // end that indicate the message length is
    // the encoded and encrypted version of the
    // extended digital signature.  He extracts
    // it.
     String bobExtractedSignature =
          bobSignedMsg.substring(
            MsgLen,bobSignedMsg.length() - 6);
    System.out.println(
        "\n14. Bob's extracted extended digital "
                    + "signature: " 
                        + bobExtractedSignature);
    byte[] strtodecrypt=bobExtractedSignature.getBytes();

            byte[] decryptedCardNo = obj.rsaDecrypt(strtodecrypt,PbkeyPath);
         String decryptedform = obj.byteArrayToHexStr(decryptedCardNo);
         System.out.println("After Decryption: "+decryptedform);

在上面的代码行中

byte[] decryptedCardNo = obj.rsaDecrypt(strtodecrypt,PbkeyPath);

调用函数:

public byte[] rsaDecrypt(byte[] sampleText,String pbkeypath) {
    PublicKey pubKey = null;
    try {
        pubKey = readKeyFromFile(pbkeypath);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    Cipher cipher = null;
    try {
        cipher = Cipher.getInstance("RSA");
    } catch (NoSuchAlgorithmException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (NoSuchPaddingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {
        cipher.init(Cipher.DECRYPT_MODE, pubKey);
    } catch (InvalidKeyException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    byte[] cipherData = null;
    try {
        cipherData = cipher.doFinal(sampleText);
        // cipherData = cipher.
    } catch (IllegalBlockSizeException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (BadPaddingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return cipherData;
}

但它给出了以下错误:

javax.crypto.IllegalBlockSizeException: Data must not be longer than 128 bytes
at com.sun.crypto.provider.RSACipher.a(DashoA13*..)
at com.sun.crypto.provider.RSACipher.engineDoFinal(DashoA13*..)
at javax.crypto.Cipher.doFinal(DashoA13*..)

我不明白如何解决 block 大小异常的错误......如果有人可以帮助我一些想法，这将对我的项目有很大帮助。

Answer 1

分组密码(例如 RSA)只能加密不超过 blockSize 字节。如果您想使用相同的 key 加密任意大量的数据，您可以将其拆分为blockSize的部分，并单独加密每个 block 。这同样适用于解密。