将 JavaScript 解密重构为 C# - AES 128

Question

我需要使用可工作的 JavaScript 来解密消息并将其转换为 C#。我有解密信息（下面的“解密”变量），如下所示：AES-128:<salt>:<iv>:<key>。这是 JavaScript：

function decodeString(message, decrypt) {
    var parts = decrypt.split(':', 4);
    var salt = CryptoJS.enc.Hex.parse(parts[1]);
    var iv = CryptoJS.enc.Hex.parse(parts[2]);
    var key = CryptoJS.PBKDF2(parts[3], salt, { keySize: 128/32, iterations: 100 });
    try {
        message = message.replace(/\s+/g, '');
        var d = CryptoJS.AES.decrypt(message, key, { iv: iv, mode: CryptoJS.mode.CBC, padding: CryptoJS.pad.Pkcs7 });
        message = d.toString(CryptoJS.enc.Utf8);
    } catch (e) {
        console.error("Encountered a problem decrypting and encrypted page!");
        console.log(e);
    }
    
    return(message);       
}

这是我在 C# 中的内容，但在 CreateDecryptor 调用中出现异常。

using System.Security.Cryptography;

private string DecodeString(string message, string decrypt)
{
    string[] parts = decrypt.ToString().Split(':');
    byte[] salt = Encoding.UTF8.GetBytes(parts[1]);
    byte[] iv = Encoding.UTF8.GetBytes(parts[2]);
    var pbkdf2 = new Rfc2898DeriveBytes(parts[3], salt, 100);
    int numKeyBytes = 128;  // Not sure this is correct
    byte[] key = pbkdf2.GetBytes(numKeyBytes);

    string plainText = null;
    using (AesManaged aes = new AesManaged())
    {
        aes.KeySize = numKeyBytes;  // Not sure if this is correct
        aes.BlockSize = 128;    // Defaults to 128, but not sure this is correct
        aes.Mode = CipherMode.CBC;
        aes.Padding = PaddingMode.PKCS7;

        try
        {
            // The below line has the following exception:
            //    The specified key is not a valid size for this algorithm.
            //    Parameter name: key
            using (var decrypter = aes.CreateDecryptor(key, iv))
            using (var plainTextStream = new MemoryStream())
            {
                using (var decrypterStream = new CryptoStream(plainTextStream, decrypter, CryptoStreamMode.Write))
                using (var binaryWriter = new BinaryWriter(decrypterStream))
                {
                    string encryptedText = Regex.Replace(message, @"\s+", "");
                    binaryWriter.Write(encryptedText);
                }
                byte[] plainTextBytes = plainTextStream.ToArray();
                plainText = Encoding.UTF8.GetString(plainTextBytes);
            }
        }
        catch (Exception ex)
        {
            log.Error("Unable to decrypt message.", ex);
        }

        return plainText;
    }
}

任何建议将不胜感激！

Answer 1

在C#代码中存在以下问题：

• Salt 和 IV 必须经过十六进制解码（而不是 UTF8 编码）。
• numKeyBytes 以字节为单位指定密钥大小，因此对于 AES-128 为 16（而不是 128）。
• aes.KeySize 以位为单位指定密钥大小，因此是 numKeyBytes * 8（而不是 numKeyBytes），但也可以省略。
• 对于aes.BlockSize、aes.Mode 和aes.Padding，使用默认值（128、CBC、PKCS7），因此无需明确指定。
• encryptedText 必须经过 Base64 解码。

一个可能的实现是：

private string Decrypt(string message, string decrypt)
{
    string[] parts = decrypt.ToString().Split(':');
    byte[] salt = StringToByteArray(parts[1]);                                                              // Hex decode salt                                            
    byte[] iv = StringToByteArray(parts[2]);                                                                // Hex dedoce IV                                           
    var pbkdf2 = new Rfc2898DeriveBytes(parts[3], salt, 100);
    int numKeyBytes = 16;                                                                                   // AES-128 key size in bytes: 16
    byte[] key = pbkdf2.GetBytes(numKeyBytes);

    string plainText = null;
    using (AesManaged aes = new AesManaged())
    {
        aes.KeySize = 192;
        try
        {
            string encryptedText = Regex.Replace(message, @"\s+", "");
            using (var decrypter = aes.CreateDecryptor(key, iv))
            using (MemoryStream msDecrypt = new MemoryStream(Convert.FromBase64String(encryptedText)))      // Base64 decode ciphertext
            {
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decrypter, CryptoStreamMode.Read))
                {
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {
                        plainText = srDecrypt.ReadToEnd();
                    }
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Unable to decrypt message.", ex);
        }

        return plainText;
    }
}

StringToByteArray() 来自here。

我将 Stream 部分更改为类似于 this example，但原始实现也可以正常工作，因此此更改是可选的。

测试：两个代码都返回数据

message = "YhyXEjjNAnRUUONwVzlha59tRoWkeEwTkOtSKOicRd/iBKkGgIp+DeWmvEXxAU53";
decrypt = "AES-128:30313233343536373839303132333435:35343332313039383736353433323130:my passphrase";

明文：

The quick brown fox jumps over the lazy dog