如何在C#中实现PHP的AES-256-CBC加密（openssl_encrypt）

对接第三方API时，要求按照以下PHP示例实现POST请求payload的加密，但只能使用C#开发：

class RESTfulAPI {
        
    function __construct($DomainOrIP, $Key, $Secret) {
        $this->BaseUri = $DomainOrIP ."/api/v2/";
        $this->ApiKey = $Key;
        $this->ApiSecret = $Secret;
        // Encryption vector initialization
        $this->SecretIV = substr(hash("SHA256", $this->ApiKey, true), 0, 16);
    }
    
    function base64Url_Encode($data) {
        return rtrim(strtr(base64_encode($data), '+/', '-_'), '=');
    }
    
    // Encryption for properties
    function APIEncryptData($Data) {
        $output = openssl_encrypt(
            $Data, 
            "AES-256-CBC", 
            md5($this->ApiSecret),
            OPENSSL_RAW_DATA, 
            $this->SecretIV);
        return $this->base64Url_Encode($output);
    }
}

加密逻辑说明 #

该PHP示例的核心加密规则：

• 加密模式：AES-256-CBC
• 密钥：ApiSecret的MD5哈希值
• IV向量：ApiKey经SHA256哈希后取前16位字节
• 输出：加密后的原始字节做Base64Url编码（替换+为-、/为_，去除末尾=）

已实现的C#辅助方法 #

已完成与PHP等效的SHA256、MD5哈希及Base64Url编码方法：

private static byte[] Sha256(string input)
{
    using (SHA256 sha = SHA256.Create())
    {
        return sha.ComputeHash(System.Text.Encoding.UTF8.GetBytes(input));
    }
}

private static byte[] Md5(string input)
{
    using (MD5 md5 = MD5.Create())
    {
        return md5.ComputeHash(System.Text.Encoding.UTF8.GetBytes(input));
    }
}

private string Base64UrlEncode(byte[] data)
{
    var base64 = Convert.ToBase64String(data);
    base64 = base64.Replace("+", "-").Replace("/", "_").TrimEnd('=');
    return base64;
}

尝试的C#加密实现 #

已尝试原生AES和BouncyCastle两种方式，但结果均与PHP不一致：

// 初始化参数
_secretIV = Sha256(Key).Take(16).ToArray();
_hashedApiKey = Md5(Secret);

// 原生AES实现
private string APIEncryptDataV1(string data)
{
    using (var aes = Aes.Create())
    {
        aes.Key = _hashedApiKey;
        aes.IV = _secretIV;
        aes.Mode = CipherMode.CBC;

        using (var encryptor = aes.CreateEncryptor())
        {
            using (var msEncrypt = new MemoryStream())
            {
                using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    using (var swEncrypt = new StreamWriter(csEncrypt))
                    {
                        swEncrypt.Write(data);
                    }
                    return Base64UrlEncode(msEncrypt.ToArray());
                }
            }
        }
    }
}

// BouncyCastle实现
public string APIEncryptDataV2(string data)
{
    var dataBytes = Encoding.UTF8.GetBytes(data);
    
    // Create AES Engine
    AesEngine engine = new AesEngine();

    // Create CBC Mode
    CbcBlockCipher blockCipher = new CbcBlockCipher(engine);

    // Create Padding
    Pkcs7Padding padding = new Pkcs7Padding();

    // Create BufferedBlockCipher
    BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(blockCipher, padding);

    // Create Key Parameter
    KeyParameter keyParam = new KeyParameter(_hashedApiKey);

    // Create IV Parameter
    ParametersWithIV ivParam = new ParametersWithIV(keyParam, _secretIV);

    // Init Cipher
    cipher.Init(true, ivParam);

    // Encrypt Data
    var output = new byte[cipher.GetOutputSize(dataBytes.Length)];
    int outputLength = cipher.ProcessBytes(dataBytes, output, 0);
    cipher.DoFinal(output, outputLength);
    
    return Base64UrlEncode(output);
}

测试样本及结果 #

Key: Q8ZHQ8P5RH5V1RVYS29S3XHDV4PTS7XX
Secret: 527L1MDDQ7WDNDZ13ZHWLNY2D7JV5LXX
Data: Test123

PHP APIEncryptData result: xwMzbdEVqer8Py-c9hapFQ
C# APIEncryptDataV1 result: fcklnK82vuNT3DlLJF8h1A
C# APIEncryptDataV2 result: fcklnK82vuNT3DlLJF8h1A

两种C#实现的结果一致，但均与PHP的加密结果不符，缺乏密码学经验无法定位问题，请求排查错误。

内容的提问来源于stack exchange，提问作者Francesco Bonizzi