如何使用 BouncyCastle Blowfish 实现解密数据？答案

【问题标题】：How to decrypt data using the BouncyCastle Blowfish implementation?如何使用 BouncyCastle Blowfish 实现解密数据？
【发布时间】：2021-05-27 22:16:04
【问题描述】：

我正在使用一个外部 API，它返回一个 Blowfish 加密 JSON 数组。首先，我尝试根据这篇文章c# Bouncy Castle Blowfish Decryption - Pad block corrupted 使用 BountyCastle 包实现 Blowfish 加密/解密方法。

internal class Program
{
    private static void Main(string[] args)
    {
        string key = "KgKnVRujrgAv4XjD4bKCqdQVN5De0DCw8zpu1URnPw8="; // random
        string content = "[{'id':1},{'id':2}]";

        string encryptedContent = Encrypt(content, key);
        string decryptedContent = Decrypt(encryptedContent, key);

        /*
         
            decryptedContent returns 
        
                [{'id':1},{'id':2}]\0\0\0\0\0

            so I think this should be fine
         
         */
    }

    private static string Encrypt(string content, string encryptionKey)
    {
        byte[] contentBytes = Encoding.UTF8.GetBytes(content);

        return SharedCode(
            contentBytes,
            encryptionKey,
            true,
            encryptedContentBytes => BitConverter
                .ToString(encryptedContentBytes)
                .Replace("-", ""));
    }

    private static string Decrypt(string encryptedContent, string decryptionKey)
    {
        byte[] contentBytes = Hex.Decode(encryptedContent);

        return SharedCode(contentBytes, decryptionKey, false, decryptedContentBytes =>
        {
            string decryptedContentString = BitConverter
                .ToString(decryptedContentBytes)
                .Replace("-", "");

            byte[] hexBytes = new byte[decryptedContentString.Length / 2];
            
            for (int i = 0; i < hexBytes.Length; i++)
            {
                string currentHexString = decryptedContentString.Substring(i * 2, 2);
                hexBytes[i] = Convert.ToByte(currentHexString, 16);
            }

            return Encoding.UTF8.GetString(hexBytes);
        });
    }

    private static string SharedCode(byte[] contentBytes, string key, bool forceEncryption, Func<byte[], string> processor)
    {
        BlowfishEngine blowfishEngine = new BlowfishEngine();
        PaddedBufferedBlockCipher paddedBufferedBlockCipher = new PaddedBufferedBlockCipher(blowfishEngine);
        byte[] keyBytes = Encoding.UTF8.GetBytes(key);
        KeyParameter keyParameter = new KeyParameter(keyBytes);
        paddedBufferedBlockCipher.Init(forceEncryption, keyParameter);
        int outputLength = paddedBufferedBlockCipher.GetOutputSize(contentBytes.Length);
        byte[] outputBytes = new byte[outputLength];
        int processedBytes = paddedBufferedBlockCipher.ProcessBytes(contentBytes, 0, contentBytes.Length, outputBytes, 0);
        paddedBufferedBlockCipher.DoFinal(outputBytes, processedBytes);

        return processor(outputBytes);
    }
}

现在我想解密 API 响应。 Api 向我返回以下 Blowfish 加密的 JSON 正文内容

$ - 1 $ $ cb8ba9e30b19ff2a d1157421764fe503d1fa9810fb9e6c3b424a1e8d014a321f5a2fb47ec6ebc8287d4d6236448d3623be42cf927fb883ca48810037c1a62bd229f937727c272c76420eb1f630bb2856c27d10c955220a1539f64e07c5708db90787ac470cad8372ea086501981c7a53ca69740c7ccfced856e234a6801efcf1f71178e75646441ba2716ea75a75ff3e6e002ba08ad18efeef95a909c9a5c68087cc63ed138a63c6788b9bbc43f3c04d2a496660f84ac98f011d3930c61ce9d5565131d2cba65db7c9bef824dd9a6594 P>

我收到了一个解密密钥和这个 PHP 代码示例作为“文档”。响应本身包含三个组

switch 语句的字符串（例如 -1）
表示盐的十六进制字符串
表示内容的十六进制字符串

<?php
function decryptData(string $data, string $key): string{
    $matches = [];
    if(!preg_match('|^\$([^$]{2,4})\$([a-f0-9]{16,64})\$|i', $data, $matches)){
        return '';
    }
    $data = (string) substr($data, strlen($matches[0]));
    switch($matches[1]){
        default:
            return '';
        case '-1':
            $data = (string) hex2bin($data);
        case '-1a':
            $algo = 'blowfish';
            return (string) openssl_decrypt($data, $algo, (string) base64_decode($key), OPENSSL_RAW_DATA, (string) hex2bin($matches[2]));
    }
}

我个人不知道盐的用途是什么，因为我的实现不需要它，但我尝试将我的代码更新为此

internal class Program
{
    private static void Main(string[] args)
    {
        string key = "KgKnVRujrgAv4XjD4bKCqdQVN5De0DCw8zpu1URnPw8"; // this decryption key is not the correct one to use
        string apiResponse = "$-1$cb8ba9e30b19ff2a$d1157421764fe503d1fa9810fb9e6c3b424a1e8d014a321f5a2fb47ec6ebc8287d4d6236448d3623be42cf927fb883ca48810037c1a62bd229f937727c272c76420eb1f630bb2856c27d10c955220a1539f64e07c5708db90787ac470cad8372ea086501981c7a53ca69740c7ccfced856e234a6801efcf1f71178e75646441ba2716ea75a75ff3e6e002ba08ad18efeef95a909c9a5c68087cc63ed138a63c6788b9bbc43f3c04d2a496660f84ac98f011d3930c61ce9d5565131d2cba65db7c9bef824dd9a6594";

        Match matches = Regex.Match(apiResponse, @"^\$([^$]{2,4})\$([a-f0-9]{16,64})\$([a-f0-9]*)");
        Group algorithm = matches.Groups[1];
        Group salt = matches.Groups[2];
        Group content = matches.Groups[3];
        string encryptedContent = content.ToString();
        string decryptedContent = Decrypt(encryptedContent, key);
    }

    private static string Decrypt(string encryptedContent, string decryptionKey)
    {
        byte[] contentBytes = Hex.Decode(encryptedContent);
        BlowfishEngine blowfishEngine = new BlowfishEngine();
        PaddedBufferedBlockCipher paddedBufferedBlockCipher = new PaddedBufferedBlockCipher(blowfishEngine);
        byte[] keyBytes = Encoding.UTF8.GetBytes(decryptionKey);
        KeyParameter keyParameter = new KeyParameter(keyBytes);
        paddedBufferedBlockCipher.Init(false, keyParameter);
        int outputLength = paddedBufferedBlockCipher.GetOutputSize(contentBytes.Length);
        byte[] outputBytes = new byte[outputLength];
        int processedBytes = paddedBufferedBlockCipher.ProcessBytes(contentBytes, 0, contentBytes.Length, outputBytes, 0);
        paddedBufferedBlockCipher.DoFinal(outputBytes, processedBytes); // throws Org.BouncyCastle.Crypto.InvalidCipherTextException: 'pad block corrupted'

        string decryptedContentString = BitConverter
            .ToString(outputBytes)
            .Replace("-", "");

        byte[] hexBytes = new byte[decryptedContentString.Length / 2];

        for (int i = 0; i < hexBytes.Length; i++)
        {
            string currentHexString = decryptedContentString.Substring(i * 2, 2);
            hexBytes[i] = Convert.ToByte(currentHexString, 16);
        }

        return Encoding.UTF8.GetString(hexBytes);
    }
}

不幸的是代码在

paddedBufferedBlockCipher.DoFinal(outputBytes, processedBytes);

抛出一个

Org.BouncyCastle.Crypto.InvalidCipherTextException：“垫块损坏”

异常。有人知道如何解密这个 Api 响应吗？

【问题讨论】：

可能仍然与编码有关。可能内容不是 UTF8。
我也尝试了Encoding.ASCII.GetBytes(content);，但得到了同样的错误......
数据是十六进制编码的，所以对它进行十六进制解码。 $ 表示一种特殊的格式，让我想起了密码的 Unix crypt 格式。在这种情况下，它不是加密，而是散列
@PresidentJamesK.Polk 抱歉，我不明白。我已经在尝试使用Hex.Decode(content) 对其进行解码
好的，对。 Hex.Decode() 需要有效的十六进制字符，“$”和“-”无效。但重点是您需要查阅“外部 API”的文档以了解这种特定的数据格式。 “-1”算法究竟是什么意思？

标签： c# encryption bouncycastle blowfish

【解决方案1】：

PHP 代码首先将这三个部分分开。第二部分是 IV，它是十六进制解码的，因此大小为 8 个字节。第三部分是数据，由于第一部分中的 -1，首先进行十六进制解码，然后使用密钥和 IV 在 CBC 模式下应用 Blowfish 和 PKCS7 填充进行解密。

要检查 C# 实现，测试数据很有用：

作为 20 字节密钥，应用以下 Base64 解码密钥：

  MDEyMzQ1Njc4OTAxMjM0NTY3ODk=

由于使用密文：

  $-1$cb8ba9e30b19ff2a$1cb8430f6b9c109e4334874408dbd26be36b0c9600383d63afd70669efcec38bea1290dfbe6b71519b1f48b514957845

如果您在 PHP 代码中使用此数据，decryptData() 将返回：

The quick brown fox jumps over the lazy dog

必须在 C# 代码中进行以下更改：

考虑静脉输液
使用 CBC 模式和 PKCS7 填充
密钥的 Base64 解码

这个结果例如在下面的实现中：

private static void Main(string[] args)
{
    //string key = "KgKnVRujrgAv4XjD4bKCqdQVN5De0DCw8zpu1URnPw8"; // this decryption key is not the correct one to use
    //string apiResponse = "$-1$cb8ba9e30b19ff2a$d1157421764fe503d1fa9810fb9e6c3b424a1e8d014a321f5a2fb47ec6ebc8287d4d6236448d3623be42cf927fb883ca48810037c1a62bd229f937727c272c76420eb1f630bb2856c27d10c955220a1539f64e07c5708db90787ac470cad8372ea086501981c7a53ca69740c7ccfced856e234a6801efcf1f71178e75646441ba2716ea75a75ff3e6e002ba08ad18efeef95a909c9a5c68087cc63ed138a63c6788b9bbc43f3c04d2a496660f84ac98f011d3930c61ce9d5565131d2cba65db7c9bef824dd9a6594";

    string key = "MDEyMzQ1Njc4OTAxMjM0NTY3ODk=";
    string apiResponse = "$-1$cb8ba9e30b19ff2a$1cb8430f6b9c109e4334874408dbd26be36b0c9600383d63afd70669efcec38bea1290dfbe6b71519b1f48b514957845";

    Match matches = Regex.Match(apiResponse, @"^\$([^$]{2,4})\$([a-f0-9]{16,64})\$([a-f0-9]*)");
    Group algorithm = matches.Groups[1];
    Group iv = matches.Groups[2];                                                               // 2nd part is the IV
    Group content = matches.Groups[3];      

    string decryptedContent = Decrypt(content.ToString(), key, iv.ToString());                  // Pass additionally the IV
    Console.WriteLine(decryptedContent);
}

private static string Decrypt(string encryptedContent, string decryptionKey, string iv)
{
    byte[] contentBytes = Hex.Decode(encryptedContent);

    byte[] keyBytes = Convert.FromBase64String(decryptionKey);                                  // Base64 decode the key
    KeyParameter keyParameter = new KeyParameter(keyBytes);
    ParametersWithIV keyParamWithIv = new ParametersWithIV(keyParameter, Hex.Decode(iv));       // Consider the IV

    BlowfishEngine blowfishEngine = new BlowfishEngine(); 
    PaddedBufferedBlockCipher paddedBufferedBlockCipher = new PaddedBufferedBlockCipher(new CbcBlockCipher(blowfishEngine), new Pkcs7Padding()); // Consider CBC mode and PKCS7 padding
    paddedBufferedBlockCipher.Init(false, keyParamWithIv);
    int outputLength = paddedBufferedBlockCipher.GetOutputSize(contentBytes.Length);
    byte[] outputBytes = new byte[outputLength];
    int processedBytes = paddedBufferedBlockCipher.ProcessBytes(contentBytes, 0, contentBytes.Length, outputBytes, 0);
    processedBytes += paddedBufferedBlockCipher.DoFinal(outputBytes, processedBytes); 
    
    return Encoding.UTF8.GetString(outputBytes, 0, processedBytes); // The quick brown fox jumps over the lazy dog
}

如果执行此代码，则测试明文结果。因此，使用此代码，您的密文应该可以使用您的密钥解密。

【讨论】：