JAVA rsa解密cipher.dofinal返回0大小数组

Question

Here is my encryption code...

private static boolean RsaEncrypt() throws CertificateException, FileNotFoundException, NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException {
    // TODO encrypt input file ans write output file
    String plainText="";
    Scanner sc=new Scanner(mTargetFile);
    while(sc.hasNextLine()){
        plainText+=sc.nextLine();
    }

    FileInputStream fin=new FileInputStream(mKeyFile);
    CertificateFactory factory=CertificateFactory.getInstance("X.509");
    X509Certificate cert=(X509Certificate) factory.generateCertificate(fin);
    PublicKey pk=cert.getPublicKey();

    Cipher cipher=Cipher.getInstance("RSA");
    cipher.init(Cipher.ENCRYPT_MODE, pk);

    byte[] bytePlain= cipher.doFinal(plainText.getBytes(StandardCharsets.UTF_8));
    String encrypted=Base64.getEncoder().encodeToString(bytePlain);
    writeFile(encrypted, mTargetFile.getName()+"_enc.txt");

    return false;
}

and here is my decryption code. It is weird cause it works well when plaintext only contains 'English'. If I put Korean in plain text, it returns 0 size array.

I have no idea what happens...

private static <privateKey> boolean RsaDecrypt() throws KeyStoreException, IOException, UnrecoverableEntryException, NoSuchAlgorithmException, CertificateException, NoSuchPaddingException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, NoSuchProviderException {
    char[] password = getPassword();
    String alias="alice";

    byte[] cipherText=Files.readAllBytes(mTargetFile.toPath());
    String cipherString=new String(cipherText, StandardCharsets.UTF_8);
    System.err.println(cipherString.length());
    // TODO decrypt input file and write output file
    KeyStore keystore=KeyStore.getInstance("PKCS12");
    FileInputStream fin=new FileInputStream(mKeyFile);
    keystore.load(fin, password);
    PrivateKey privateKey=(PrivateKey)keystore.getKey(alias, password);
    //KeyStore.PrivateKeyEntry privateKeyEntry= (KeyStore.PrivateKeyEntry) keystore.getEntry(alias, new KeyStore.PasswordProtection(password));

    Cipher cipher=Cipher.getInstance("RSA");
    byte[] encryptedByte= Base64.getDecoder().decode(cipherString.getBytes(StandardCharsets.UTF_8));
    System.err.println(encryptedByte.length);
    cipher.init(Cipher.DECRYPT_MODE, privateKey);
    byte[] decryptedByte=cipher.doFinal(encryptedByte);
    System.err.println(decryptedByte.length);

    writeFile(decryptedByte, mTargetFile.getName()+"_dec.txt");
    return false;
}

Answer 1

Your encryption/decryption code looks good. Not sure about KeyStore or file handling, but Cipher usage is ok. I did test it, and got proper result even with Korean letters. Are you sure you didn't hide some crucial stack trace errors?

I could guess you are trying to encrypt too long plain message. Using raw RSA you can encrypt only limited short messages. With 1024 bits RSA key you can encrypt only 117 bytes of data. If you need to encrypt longer messages you should use symmetric encryption like AES. Usually you encrypt message with AES, and then encrypt AES key with RSA key.