SAML RSA和AES解密-末尾的随机垃圾字节

Question

public static void main(String[] args) throws Exception {
    Path p = Paths.get("C:\\Users\\jj\\Desktop\\myPrivateKey.key");
    String encryptedAESKey = "FUZLPtkLSUgOo0bETQ5hwP1OWNggGlWhG+Z......wF1G6twRjg=="; // from XML
    byte[] aesKey = decryptWithPem("RSA/ECB/OAEPwithSHA1andMGF1Padding", "RSA", Util.base64DecodeAsBytes(encryptedAESKey), p);
    String encryptedXML = "YfJu7h4Id09hpuoqthl3Ks/JqhIXm.....amb24JZu7cJZT3cEO2a2U6qi0VCyoXQ=";
    byte[] decryptedData = decrypt("AES/CBC/NoPadding", "AES", Util.base64DecodeAsBytes(encryptedXML), aesKey);
    for(int i = decryptedData.length - 20; i < decryptedData.length; i++) {
        System.out.println("i: " + i + " -> " + decryptedData[i]); // print last 20 bytes
    }
    System.out.println(new String(decryptedData)); // prints <saml2:Assertion xmlns:saml2="urn:oasis:names:........</saml2:Assertion>�G{A

}

g{a

我意识到消息中的前16个字节是IV，所以我从消息中去掉了它们（从消息开始就去掉了垃圾）。但是现在我在消息的末尾得到了随机的5个字节。这些字节是：

i: 1931 -> -120
i: 1932 -> 71
i: 1933 -> 123
i: 1934 -> 65
i: 1935 -> 5

其他职能：

public static byte[] decryptWithPem(String alg, String pemAlg, byte[] encryptedData, Path pemPath) {
    try {
        Cipher cipher = Cipher.getInstance(alg, "BC");
        cipher.init(Cipher.DECRYPT_MODE, loadPrivateKey(pemPath, pemAlg));
        return cipher.doFinal(encryptedData);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

private static PrivateKey loadPrivateKey(Path keyPath, String alg) {
    try {
        byte[] keyData = Util.base64DecodeAsBytes(IOUtil.fileToString(keyPath).replaceAll("\\s", ""));
        KeyFactory keyFactory = KeyFactory.getInstance(alg);
        EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(keyData);
        return keyFactory.generatePrivate(privateKeySpec);
    } catch(NoSuchAlgorithmException | InvalidKeySpecException e) {
        throw new RuntimeException(e);
    }
}

private static SecretKeySpec getSecretKeySpec(String alg, byte[] key) {
    return new SecretKeySpec(key, alg);
}

public static byte[] decrypt(String alg, String keyAlg, byte[] dataToDecrypt, byte[] key) {
    try {
        Cipher cipher = Cipher.getInstance(alg, "BC");
        cipher.init(Cipher.DECRYPT_MODE, getSecretKeySpec(keyAlg, key), new IvParameterSpec(dataToDecrypt, 0, 16));
        return cipher.doFinal(Arrays.copyOfRange(dataToDecrypt, 16, dataToDecrypt.length));
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

消息有没有可能是随机填充的？

-----编辑-----

看来规范使用的是ISO10126填充，用“AES/CBC/ISO10126Padding”代替“AES/CBC/NOPadding”。

Answer 1

消息有没有可能是随机填充的？

是的，正如填充部分所详述的，它使用随机填充，表示问号可以是任何值，但最后一个字节表示填充的长度。他们的示例:0x2122232425262728？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？08。

这实际上是ISO10126填充,您可以通过查看最后一个字节轻松地将其删除：

byte[] pp = cipher.doFinal(Arrays.copyOfRange(dataToDecrypt, 16, dataToDecrypt.length));
return Arrays.copyOf(pp, pp.length - pp[pp.length-1]);