# 使用 C\$1 和 .NET Framework 创建 URL 签名


本节中的 C\$1 示例实现了一个示例应用程序，该程序演示了如何使用标准和自定义策略声明为 CloudFront 私有分配创建签名。此示例包括基于 [适用于 .NET 的 Amazon SDK](https://www.amazonaws.cn/sdkfornet) 的实用工具函数，这些函数在 .NET 应用程序中非常有用。

还可以通过使用 适用于 .NET 的 Amazon SDK 创建签名 URL 和签名 Cookie。在 *适用于 .NET 的 Amazon SDK API 参考*中，请参阅以下主题：
+ **签名 URL** – [AmazonCloudFrontUrlSigner](https://docs.amazonaws.cn/sdkfornet/v3/apidocs/items/CloudFront/TCloudFrontUrlSigner.html) 
+ **签名 Cookie** – [AmazonCloudFrontCookieSigner](https://docs.amazonaws.cn/sdkfornet/v3/apidocs/items/CloudFront/TCloudFrontCookieSigner.html) 

要下载代码，请转到 [C\$1 签名代码](https://docs.amazonaws.cn/AmazonCloudFront/latest/DeveloperGuide/samples/AWS_PrivateCF_Distributions.zip)。

**备注**  
`AmazonCloudFrontUrlSigner` 和 `AmazonCloudFrontCookieSigner` 类已移至单独的包。有关使用它们的更多信息，请参阅《适用于 .NET 的 Amazon SDK (V4) Developer Guide》**中的 [CookieSigner and UrlSigner](https://docs.amazonaws.cn/sdk-for-net/v4/developer-guide/net-dg-v4.html#net-dg-v4-CookieSigner-UrlSigner)。
创建 URL 签名只是使用签名 URL 提供私有内容过程的一部分。有关更多信息，请参阅 [使用签名 URL](private-content-signed-urls.md)。有关使用签名 Cookie 的更多信息，请参阅[使用签名 Cookie](private-content-signed-cookies.md)。

## 在 .NET 框架中使用 RSA 密钥


要在 .NET 框架中使用 RSA 密钥，您必须将 Amazon 提供的 .pem 文件转换为 .NET 框架使用的 XML 格式。

转换之后，RSA 私有密钥文件是以下格式：

**Example ：XML .NET 框架格式的 RSA 私有密钥**  <a name="RSAPrivateKeyXML.NETFrameworkFormat"></a>

```
<RSAKeyValue>
  <Modulus>
    wO5IvYCP5UcoCKDo1dcspoMehWBZcyfs9QEzGi6Oe5y+ewGr1oW+vB2GPB
    ANBiVPcUHTFWhwaIBd3oglmF0lGQljP/jOfmXHUK2kUUnLnJp+oOBL2NiuFtqcW6h/L5lIpD8Yq+NRHg
    Ty4zDsyr2880MvXv88yEFURCkqEXAMPLE=
  </Modulus>
  <Exponent>AQAB</Exponent>
  <P>
    5bmKDaTz
    npENGVqz4Cea8XPH+sxt+2VaAwYnsarVUoSBeVt8WLloVuZGG9IZYmH5KteXEu7fZveYd9UEXAMPLE==
  </P>
  <Q>
    1v9l/WN1a1N3rOK4VGoCokx7kR2SyTMSbZgF9IWJNOugR/WZw7HTnjipO3c9dy1Ms9pUKwUF4
    6d7049EXAMPLE==
  </Q>
  <DP>
    RgrSKuLWXMyBH+/l1Dx/I4tXuAJIrlPyo+VmiOc7b5NzHptkSHEPfR9s1
    OK0VqjknclqCJ3Ig86OMEtEXAMPLE==
  </DP>
  <DQ>
    pjPjvSFw+RoaTu0pgCA/jwW/FGyfN6iim1RFbkT4
    z49DZb2IM885f3vf35eLTaEYRYUHQgZtChNEV0TEXAMPLE==
  </DQ>
  <InverseQ>
    nkvOJTg5QtGNgWb9i
    cVtzrL/1pFEOHbJXwEJdU99N+7sMK+1066DL/HSBUCD63qD4USpnf0myc24in0EXAMPLE==</InverseQ>
  <D>
      Bc7mp7XYHynuPZxChjWNJZIq+A73gm0ASDv6At7F8Vi9r0xUlQe/v0AQS3ycN8QlyR4XMbzMLYk
      3yjxFDXo4ZKQtOGzLGteCU2srANiLv26/imXA8FVidZftTAtLviWQZBVPTeYIA69ATUYPEq0a5u5wjGy
      UOij9OWyuEXAMPLE=
   </D>
</RSAKeyValue>
```

## C\$1 中的标准策略签名方法


以下 C\$1 代码通过执行以下步骤创建使用标准策略的签名 URL：
+ 创建策略声明。
+ 使用 SHA1 对策略声明进行哈希处理，并使用 RSA 和其相应公有密钥位于可信密钥组中的私有密钥对结果进行签名。
+ 对经过哈希及签署的策略声明进行 Base64 编码，并替换使字符串能够安全地用作 URL 请求参数的特殊字符。
+ 联接值。

有关完整实现，请参阅 [C\$1 签名代码](https://docs.amazonaws.cn/AmazonCloudFront/latest/DeveloperGuide/samples/AWS_PrivateCF_Distributions.zip)中的示例。

**注意**  
当您将公有密钥上传到 CloudFront 时，会返回 `keyId`。有关更多信息，请参阅 ![\[6\]](http://docs.amazonaws.cn/AmazonCloudFront/latest/DeveloperGuide/images/callouts/6.png)[ &Key-Pair-Id](private-content-creating-signed-url-canned-policy.md)。

**Example ：C\$1 中的标准策略签名方法**  <a name="ExampleCannedPolicySigningMethod-CSharp"></a>

```
public static string ToUrlSafeBase64String(byte[] bytes)
{
    return System.Convert.ToBase64String(bytes)
        .Replace('+', '-')
        .Replace('=', '_')
        .Replace('/', '~');
}

public static string CreateCannedPrivateURL(string urlString, 
    string durationUnits, string durationNumber, string pathToPolicyStmnt, 
    string pathToPrivateKey, string keyId)
{
    // args[] 0-thisMethod, 1-resourceUrl, 2-seconds-minutes-hours-days 
    // to expiration, 3-numberOfPreviousUnits, 4-pathToPolicyStmnt, 
    // 5-pathToPrivateKey, 6-keyId

    TimeSpan timeSpanInterval = GetDuration(durationUnits, durationNumber);

    // Create the policy statement.
    string strPolicy = CreatePolicyStatement(pathToPolicyStmnt,
        urlString, 
        DateTime.Now, 
        DateTime.Now.Add(timeSpanInterval), 
        "0.0.0.0/0");
    if ("Error!" == strPolicy) return "Invalid time frame." + 
        "Start time cannot be greater than end time.";

    // Copy the expiration time defined by policy statement.
    string strExpiration = CopyExpirationTimeFromPolicy(strPolicy);

    // Read the policy into a byte buffer.
    byte[] bufferPolicy = Encoding.ASCII.GetBytes(strPolicy);

    // Initialize the SHA1CryptoServiceProvider object and hash the policy data.
    using (SHA1CryptoServiceProvider 
        cryptoSHA1 = new SHA1CryptoServiceProvider())
    {
        bufferPolicy = cryptoSHA1.ComputeHash(bufferPolicy);

        // Initialize the RSACryptoServiceProvider object.
        RSACryptoServiceProvider providerRSA = new RSACryptoServiceProvider();
        XmlDocument xmlPrivateKey = new XmlDocument();

        // Load your private key, which you created by converting your 
        // .pem file to the XML format that the .NET framework uses.  
        // Several tools are available. 
        xmlPrivateKey.Load(pathToPrivateKey);

        // Format the RSACryptoServiceProvider providerRSA and 
        // create the signature.
        providerRSA.FromXmlString(xmlPrivateKey.InnerXml);
        RSAPKCS1SignatureFormatter rsaFormatter = 
            new RSAPKCS1SignatureFormatter(providerRSA);
        rsaFormatter.SetHashAlgorithm("SHA1");
        byte[] signedPolicyHash = rsaFormatter.CreateSignature(bufferPolicy);

        // Convert the signed policy to URL-safe base64 encoding and 
        // replace unsafe characters + = / with the safe characters - _ ~
        string strSignedPolicy = ToUrlSafeBase64String(signedPolicyHash);

        // Concatenate the URL, the timestamp, the signature, 
        // and the key pair ID to form the signed URL.
        return urlString + 
            "?Expires=" + 
            strExpiration + 
            "&Signature=" + 
            strSignedPolicy + 
            "&Key-Pair-Id=" + 
            keyId;
    }
}
```

## C\$1 中自定义策略签名方法


以下 C\$1 代码通过执行以下步骤创建使用自定义策略的签名 URL：

1. 创建策略声明。

1. 对策略声明进行 Base64 编码，并替换使字符串能够安全地用作 URL 请求参数的特殊字符。

1. 使用 SHA1 对策略声明进行哈希处理，并使用 RSA 和其相应公有密钥位于可信密钥组中的私有密钥对结果进行加密。

1. 对经过哈希的策略声明进行 Base64 编码，并替换使字符串能够安全地用作 URL 请求参数的特殊字符。

1. 联接值。

有关完整实现，请参阅 [C\$1 签名代码](https://docs.amazonaws.cn/AmazonCloudFront/latest/DeveloperGuide/samples/AWS_PrivateCF_Distributions.zip)中的示例。

**注意**  
当您将公有密钥上传到 CloudFront 时，会返回 `keyId`。有关更多信息，请参阅 ![\[6\]](http://docs.amazonaws.cn/AmazonCloudFront/latest/DeveloperGuide/images/callouts/6.png)[ &Key-Pair-Id](private-content-creating-signed-url-canned-policy.md)。

**Example ：C\$1 中的自定义策略签名方法**  <a name="ExampleCustomPolicySigningMethod-CSharp"></a>

```
public static string ToUrlSafeBase64String(byte[] bytes)
{
    return System.Convert.ToBase64String(bytes)
        .Replace('+', '-')
        .Replace('=', '_')
        .Replace('/', '~');
}

public static string CreateCustomPrivateURL(string urlString, 
    string durationUnits, string durationNumber, string startIntervalFromNow, 
    string ipaddress, string pathToPolicyStmnt, string pathToPrivateKey, 
    string keyId)
{
    // args[] 0-thisMethod, 1-resourceUrl, 2-seconds-minutes-hours-days 
    // to expiration, 3-numberOfPreviousUnits, 4-starttimeFromNow, 
    // 5-ip_address, 6-pathToPolicyStmt, 7-pathToPrivateKey, 8-keyId

    TimeSpan timeSpanInterval = GetDuration(durationUnits, durationNumber);
    TimeSpan timeSpanToStart = GetDurationByUnits(durationUnits, 
        startIntervalFromNow);
    if (null == timeSpanToStart) 
        return "Invalid duration units." + 
            "Valid options: seconds, minutes, hours, or days";
            
    string strPolicy = CreatePolicyStatement(
        pathToPolicyStmnt, urlString, DateTime.Now.Add(timeSpanToStart), 
        DateTime.Now.Add(timeSpanInterval), ipaddress);

    // Read the policy into a byte buffer.
    byte[] bufferPolicy = Encoding.ASCII.GetBytes(strPolicy);

    // Convert the policy statement to URL-safe base64 encoding and 
    // replace unsafe characters + = / with the safe characters - _ ~

    string urlSafePolicy = ToUrlSafeBase64String(bufferPolicy);

    // Initialize the SHA1CryptoServiceProvider object and hash the policy data.
    byte[] bufferPolicyHash;
    using (SHA1CryptoServiceProvider cryptoSHA1 = 
        new SHA1CryptoServiceProvider())
    {
        bufferPolicyHash = cryptoSHA1.ComputeHash(bufferPolicy);

        // Initialize the RSACryptoServiceProvider object.
        RSACryptoServiceProvider providerRSA = new RSACryptoServiceProvider();
        XmlDocument xmlPrivateKey = new XmlDocument();

        // Load your private key, which you created by converting your 
        // .pem file to the XML format that the .NET framework uses.  
        // Several tools are available. 
        xmlPrivateKey.Load(pathToPrivateKey);

        // Format the RSACryptoServiceProvider providerRSA 
        // and create the signature.
        providerRSA.FromXmlString(xmlPrivateKey.InnerXml);
        RSAPKCS1SignatureFormatter RSAFormatter = 
            new RSAPKCS1SignatureFormatter(providerRSA);
        RSAFormatter.SetHashAlgorithm("SHA1");
        byte[] signedHash = RSAFormatter.CreateSignature(bufferPolicyHash);

        // Convert the signed policy to URL-safe base64 encoding and 
        // replace unsafe characters + = / with the safe characters - _ ~
        string strSignedPolicy = ToUrlSafeBase64String(signedHash);

        return urlString + 
            "?Policy=" + 
            urlSafePolicy + 
            "&Signature=" + 
            strSignedPolicy + 
            "&Key-Pair-Id=" + 
            keyId;
    }
}
```

## 用于签名生成的实用工具方法


以下方法从文件和签名生成解析时间间隔中获得策略声明。

**Example ：用于签名生成的实用工具方法**  <a name="UtilityMethodsForSignatureGeneration"></a>

```
public static string CreatePolicyStatement(string policyStmnt, 
   string resourceUrl, 
   DateTime startTime, 
   DateTime endTime, 
   string ipAddress)
   
{
   // Create the policy statement.
   FileStream streamPolicy = new FileStream(policyStmnt, FileMode.Open, FileAccess.Read);
   using (StreamReader reader = new StreamReader(streamPolicy))
   {
      string strPolicy = reader.ReadToEnd();

      TimeSpan startTimeSpanFromNow = (startTime - DateTime.Now);
      TimeSpan endTimeSpanFromNow = (endTime - DateTime.Now);
      TimeSpan intervalStart = 
         (DateTime.UtcNow.Add(startTimeSpanFromNow)) - 
         new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
      TimeSpan intervalEnd = 
         (DateTime.UtcNow.Add(endTimeSpanFromNow)) - 
         new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);

      int startTimestamp = (int)intervalStart.TotalSeconds; // START_TIME
      int endTimestamp = (int)intervalEnd.TotalSeconds;  // END_TIME

      if (startTimestamp > endTimestamp)
         return "Error!";

      // Replace variables in the policy statement.
      strPolicy = strPolicy.Replace("RESOURCE", resourceUrl);
      strPolicy = strPolicy.Replace("START_TIME", startTimestamp.ToString());
      strPolicy = strPolicy.Replace("END_TIME", endTimestamp.ToString());
      strPolicy = strPolicy.Replace("IP_ADDRESS", ipAddress);
      strPolicy = strPolicy.Replace("EXPIRES", endTimestamp.ToString());
      return strPolicy;
   }   
}

public static TimeSpan GetDuration(string units, string numUnits)
{
   TimeSpan timeSpanInterval = new TimeSpan();
   switch (units)
   {
      case "seconds":
         timeSpanInterval = new TimeSpan(0, 0, 0, int.Parse(numUnits));
         break;
      case "minutes":
         timeSpanInterval = new TimeSpan(0, 0, int.Parse(numUnits), 0);
         break;
      case "hours":
         timeSpanInterval = new TimeSpan(0, int.Parse(numUnits), 0 ,0);
         break;
      case "days":
         timeSpanInterval = new TimeSpan(int.Parse(numUnits),0 ,0 ,0);
         break;
      default:
         Console.WriteLine("Invalid time units;" + 
            "use seconds, minutes, hours, or days");
         break;
   }
   return timeSpanInterval;
}

private static TimeSpan GetDurationByUnits(string durationUnits, 
   string startIntervalFromNow)
{
   switch (durationUnits)
   {
      case "seconds":
         return new TimeSpan(0, 0, int.Parse(startIntervalFromNow));
      case "minutes":
         return new TimeSpan(0, int.Parse(startIntervalFromNow), 0);
      case "hours":
         return new TimeSpan(int.Parse(startIntervalFromNow), 0, 0);
      case "days":
         return new TimeSpan(int.Parse(startIntervalFromNow), 0, 0, 0);
      default:
         return new TimeSpan(0, 0, 0, 0);
   }
}

public static string CopyExpirationTimeFromPolicy(string policyStatement)
{
   int startExpiration = policyStatement.IndexOf("EpochTime");
   string strExpirationRough = policyStatement.Substring(startExpiration + 
      "EpochTime".Length);
   char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
         
   List<char> listDigits = new List<char>(digits);
   StringBuilder buildExpiration = new StringBuilder(20);
         
   foreach (char c in strExpirationRough)
   {
      if (listDigits.Contains(c))
         buildExpiration.Append(c);
   }
   return buildExpiration.ToString();   
}
```

另请参阅
+ [使用 Perl 创建 URL 签名](CreateURLPerl.md)
+ [使用 PHP 创建 URL 签名](CreateURL_PHP.md)
+ [使用 Java 创建 URL 签名](CFPrivateDistJavaDevelopment.md)