c# - 如何在 C# 中获得与在 PHP 单元测试中相同的 HMAC256 结果？

Question

我想我会尝试将新的签名请求逻辑添加到我的 facebook canvas 应用程序中，为了让自己“轻松”完成此操作，我去了 GitHub 上的 facebook PHP sdk 并查看了 unit tests .

我的实际问题是，我无法获取请求中包含的哈希值来匹配我使用应用程序 secret 计算的哈希值，以及在请求中发送的数据。

这意味着如何工作在 Facebook's authentication page 中有描述。 .

private string VALID_SIGNED_REQUEST = "ZcZocIFknCpcTLhwsRwwH5nL6oq7OmKWJx41xRTi59E.eyJhbGdvcml0aG0iOiJITUFDLVNIQTI1NiIsImV4cGlyZXMiOiIxMjczMzU5NjAwIiwib2F1dGhfdG9rZW4iOiIyNTQ3NTIwNzMxNTJ8Mi5JX2VURmtjVEtTelg1bm8zakk0cjFRX18uMzYwMC4xMjczMzU5NjAwLTE2Nzc4NDYzODV8dUk3R3dybUJVZWQ4c2VaWjA1SmJkekdGVXBrLiIsInNlc3Npb25fa2V5IjoiMi5JX2VURmtjVEtTelg1bm8zakk0cjFRX18uMzYwMC4xMjczMzU5NjAwLTE2Nzc4NDYzODUiLCJ1c2VyX2lkIjoiMTY3Nzg0NjM4NSJ9";

private string NON_TOSSED_SIGNED_REQUEST = "laEjO-az9kzgFOUldy1G7EyaP6tMQEsbFIDrB1RUamE.eyJhbGdvcml0aG0iOiJITUFDLVNIQTI1NiJ9";

public void SignedRequestExample()
{
 var Encoding = new UTF8Encoding();

 string ApplicationSecret = "904270b68a2cc3d54485323652da4d14"; 

 string SignedRequest = VALID_SIGNED_REQUEST;
 string ExpectedSignature = SignedRequest.Substring(0, SignedRequest.IndexOf('.'));
 string Payload = SignedRequest.Substring(SignedRequest.IndexOf('.') + 1);

 // Back & Forth with Signature
 byte[] ActualSignature = FromUrlBase64String(ExpectedSignature);
 string TestSignature = ToUrlBase64String(ActualSignature);

 // Back & Forth With Data
 byte[] ActualPayload = FromUrlBase64String(Payload);
 string Json = Encoding.GetString(ActualPayload);
 string TestPayload = ToUrlBase64String(ActualPayload);

 // Attempt to get same hash
 var Hmac = SignWithHMAC(ActualPayload, Encoding.GetBytes(ApplicationSecret));
 var HmacBase64 = ToUrlBase64String(Hmac);            
 var HmacHex = BytesToHex(Hmac);

 if (HmacBase64 != ExpectedSignature)
 {
  // YAY
 }
 else
 {
  // BOO
 }
}

private static string BytesToHex(byte[] input)
{
 StringBuilder sb = new StringBuilder();

 foreach (byte b in input)
 {
  sb.Append(string.Format("{0:x2}", b));
 }
 return sb.ToString();
}
private string ToUrlBase64String(byte[] Input)
{
 return Convert.ToBase64String(Input).Replace("=", String.Empty).Replace('+', '-').Replace('/', '_');
}

// http://tools.ietf.org/html/rfc4648#section-5            
private byte[] FromUrlBase64String(string Base64UrlSafe)
{
 Base64UrlSafe = Base64UrlSafe.PadRight(Base64UrlSafe.Length + (4 - Base64UrlSafe.Length % 4) % 4, '=');
 Base64UrlSafe = Base64UrlSafe.Replace('-', '+').Replace('_', '/');
 return Convert.FromBase64String(Base64UrlSafe);
}

private byte[] SignWithHMAC(byte[] dataToSign, byte[] keyBody)
{
 using (var hmac = new HMACSHA256(keyBody))
 {
  hmac.ComputeHash(dataToSign);
  /*
  CryptoStream cs = new CryptoStream(System.IO.Stream.Null, hmac, CryptoStreamMode.Write);
  cs.Write(dataToSign, 0, dataToSign.Length);
  cs.Flush();
  cs.Close();
  byte[] hashResult = hmac.Hash;
  */
  return hmac.Hash;
 }
}

public string Base64ToHex(string input)
{
 StringBuilder sb = new StringBuilder();
 byte[] inputBytes = Convert.FromBase64String(input);
 foreach (byte b in inputBytes)
 {
  sb.Append(string.Format("{0:x2}", b));
 }
 return sb.ToString();
}

感谢下面的 Rasmus 回答，为了帮助这里的其他人，更新了(清理代码):

/// Example signed_request variable from PHPSDK Unit Testing
private string VALID_SIGNED_REQUEST = "ZcZocIFknCpcTLhwsRwwH5nL6oq7OmKWJx41xRTi59E.eyJhbGdvcml0aG0iOiJITUFDLVNIQTI1NiIsImV4cGlyZXMiOiIxMjczMzU5NjAwIiwib2F1dGhfdG9rZW4iOiIyNTQ3NTIwNzMxNTJ8Mi5JX2VURmtjVEtTelg1bm8zakk0cjFRX18uMzYwMC4xMjczMzU5NjAwLTE2Nzc4NDYzODV8dUk3R3dybUJVZWQ4c2VaWjA1SmJkekdGVXBrLiIsInNlc3Npb25fa2V5IjoiMi5JX2VURmtjVEtTelg1bm8zakk0cjFRX18uMzYwMC4xMjczMzU5NjAwLTE2Nzc4NDYzODUiLCJ1c2VyX2lkIjoiMTY3Nzg0NjM4NSJ9";

public bool ValidateSignedRequest()
{            
    string applicationSecret = "904270b68a2cc3d54485323652da4d14";
    string[] signedRequest = VALID_SIGNED_REQUEST.Split('.');            
    string expectedSignature = signedRequest[0];
    string payload = signedRequest[1];

    // Attempt to get same hash
    var Hmac = SignWithHmac(UTF8Encoding.UTF8.GetBytes(payload), UTF8Encoding.UTF8.GetBytes(applicationSecret));
    var HmacBase64 = ToUrlBase64String(Hmac);

    return (HmacBase64 == expectedSignature);           
}


private string ToUrlBase64String(byte[] Input)
{
    return Convert.ToBase64String(Input).Replace("=", String.Empty)
                                        .Replace('+', '-')
                                        .Replace('/', '_');
}

private byte[] SignWithHmac(byte[] dataToSign, byte[] keyBody)
{
    using (var hmacAlgorithm = new HMACSHA256(keyBody))
    {
        hmacAlgorithm.ComputeHash(dataToSign);
        return hmacAlgorithm.Hash;
    }
}

Answer 1

您不应该在计算 HMAC 之前对有效负载进行 base64 解码。

使用这一行:

var Hmac = SignWithHMAC(Encoding.GetBytes(Payload), Encoding.GetBytes(ApplicationSecret));

它应该可以工作。

还有一些提示:

• 与其摆弄 Substring() 和 IndexOf()，不如尝试使用 String.Split()
• 你已经调换了 YAY 和 BOO 的评论
• 如果您遵循以小写开头的局部变量名称的通用规则(例如:var applicationSecret = "...";)，C# 代码将更具可读性