Create content keys with REST

Media Services enables you to deliver encrypted assets. A ContentKey provides secure access to your Assets.

When you create a new asset (for example, before you upload files), you can specify the following encryption options: StorageEncrypted, CommonEncryptionProtected, or EnvelopeEncryptionProtected.

When you deliver assets to your clients, you can configure for assets to be dynamically encrypted with one of the following two encryptions: DynamicEnvelopeEncryption or DynamicCommonEncryption.

Encrypted assets have to be associated with ContentKeys. This article describes how to create a content key.

The following are general steps for generating content keys that you associate with assets that you want to be encrypted.

  1. Randomly generate a 16-byte AES key (for common and envelope encryption) or a 32-byte AES key (for storage encryption).

    This is the content key for your asset, which means all files associated with that asset need to use the same content key during decryption.

  2. Call the GetProtectionKeyId and GetProtectionKey methods to get the correct X.509 Certificate that must be used to encrypt your content key.
  3. Encrypt your content key with the public key of the X.509 Certificate.

    Media Services .NET SDK uses RSA with OAEP when doing the encryption. You can see an example in the EncryptSymmetricKeyData function.

  4. Create a checksum value (based on the PlayReady AES key checksum algorithm) calculated using the key identifier and content key. For more information, see the “PlayReady AES Key Checksum Algorithm” section of the PlayReady Header Object document located here.

    The following .NET example calculates the checksum using the GUID part of the key identifier and the clear content key.

     public static string CalculateChecksum(byte[] contentKey, Guid keyId)
      {
    
          byte[] array = null;
          using (AesCryptoServiceProvider aesCryptoServiceProvider = new AesCryptoServiceProvider())
          {
              aesCryptoServiceProvider.Mode = CipherMode.ECB;
              aesCryptoServiceProvider.Key = contentKey;
              aesCryptoServiceProvider.Padding = PaddingMode.None;
              ICryptoTransform cryptoTransform = aesCryptoServiceProvider.CreateEncryptor();
              array = new byte[16];
              cryptoTransform.TransformBlock(keyId.ToByteArray(), 0, 16, array, 0);
          }
          byte[] array2 = new byte[8];
          Array.Copy(array, array2, 8);
          return Convert.ToBase64String(array2);
      }
    
  5. Create the Content key with the EncryptedContentKey (converted to base64-encoded string), ProtectionKeyId, ProtectionKeyType, ContentKeyType, and Checksum values you have received in previous steps.
  6. Associate the ContentKey entity with your Asset entity through the $links operation.

This article does not show how to generate an AES key, encrypt the key, and calculate the checksum.

Note

When accessing entities in Media Services, you must set specific header fields and values in your HTTP requests. For more information, see Setup for Media Services REST API Development.

Connect to Media Services

For information on how to connect to the AMS API, see Access the Azure Media Services API with Azure AD authentication.

Retrieve the ProtectionKeyId

The following example shows how to retrieve the ProtectionKeyId, a certificate thumbprint, for the certificate you must use when encrypting your content key. Do this step to make sure that you already have the appropriate certificate on your machine.

Request:

GET https://media.windows.net/api/GetProtectionKeyId?contentKeyType=0 HTTP/1.1
MaxDataServiceVersion: 3.0;NetFx
Accept: application/json
Accept-Charset: UTF-8
User-Agent: Microsoft ADO.NET Data Services
Authorization: Bearer <ENCODED JWT TOKEN> 
x-ms-version: 2.17
Host: media.windows.net

Response:

HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Length: 139
Content-Type: application/json;odata=minimalmetadata;streaming=true;charset=utf-8
Server: Microsoft-IIS/8.5
request-id: 2b6aa7a4-3a09-4b08-b581-26b55667f817
x-ms-request-id: 2b6aa7a4-3a09-4b08-b581-26b55667f817
X-Content-Type-Options: nosniff
DataServiceVersion: 3.0;
X-Powered-By: ASP.NET
Strict-Transport-Security: max-age=31536000; includeSubDomains
Date: Wed, 04 Feb 2015 02:42:52 GMT

{"odata.metadata":"https://wamsbayclus001rest-hs.cloudapp.net/api/$metadata#Edm.String","value":"7D9BB04D9D0A4A24800CADBFEF232689E048F69C"}

Retrieve the ProtectionKey for the ProtectionKeyId

The following example shows how to retrieve the X.509 certificate using the ProtectionKeyId you received in the previous step.

Request:

GET https://media.windows.net/api/GetProtectionKey?ProtectionKeyId='7D9BB04D9D0A4A24800CADBFEF232689E048F69C' HTTP/1.1
MaxDataServiceVersion: 3.0;NetFx
Accept: application/json
Accept-Charset: UTF-8
User-Agent: Microsoft ADO.NET Data Services
Authorization: Bearer <ENCODED JWT TOKEN> 
x-ms-version: 2.17
x-ms-client-request-id: 78d1247a-58d7-40e5-96cc-70ff0dfa7382
Host: media.windows.net

Response:

HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Length: 1227
Content-Type: application/json;odata=minimalmetadata;streaming=true;charset=utf-8
Server: Microsoft-IIS/8.5
x-ms-client-request-id: 78d1247a-58d7-40e5-96cc-70ff0dfa7382
request-id: 1523e8f3-8ed2-40fe-8a9a-5d81eb572cc8
x-ms-request-id: 1523e8f3-8ed2-40fe-8a9a-5d81eb572cc8
X-Content-Type-Options: nosniff
DataServiceVersion: 3.0;
X-Powered-By: ASP.NET
Strict-Transport-Security: max-age=31536000; includeSubDomains
Date: Thu, 05 Feb 2015 07:52:30 GMT

{"odata.metadata":"https://wamsbayclus001rest-hs.cloudapp.net/api/$metadata#Edm.String",
"value":"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"}

Create the ContentKey

After you have retrieved the X.509 certificate and used its public key to encrypt your content key, create a ContentKey entity and set its property values accordingly.

One of the values that you must set when create the content key is the type. Choose from one of the following values:

public enum ContentKeyType
{
    /// <summary>
    /// Specifies a content key for common encryption.
    /// </summary>
    /// <remarks>This is the default value.</remarks>
    CommonEncryption = 0,

    /// <summary>
    /// Specifies a content key for storage encryption.
    /// </summary>
    StorageEncryption = 1,

    /// <summary>
    /// Specifies a content key for configuration encryption.
    /// </summary>
    ConfigurationEncryption = 2,

    /// <summary>
    /// Specifies a content key for Envelope encryption.  Only used internally.
    /// </summary>
    EnvelopeEncryption = 4
}

The following example shows how to create a ContentKey with a ContentKeyType set for storage encryption ("1") and the ProtectionKeyType set to "0" to indicate that the protection key ID is the X.509 certificate thumbprint.

Request

POST https://media.windows.net/api/ContentKeys HTTP/1.1
Content-Type: application/json
DataServiceVersion: 1.0;NetFx
MaxDataServiceVersion: 3.0;NetFx
Accept: application/json
Accept-Charset: UTF-8
User-Agent: Microsoft ADO.NET Data Services
Authorization: Bearer <ENCODED JWT TOKEN> 
x-ms-version: 2.17
Host: media.windows.net
{
"Name":"ContentKey",
"ProtectionKeyId":"7D9BB04D9D0A4A24800CADBFEF232689E048F69C", 
"ContentKeyType":"1", 
"ProtectionKeyType":"0",
"EncryptedContentKey":"your encrypted content key",
"Checksum":"calculated checksum"
}

Response:

HTTP/1.1 201 Created
Cache-Control: no-cache
Content-Length: 777
Content-Type: application/json;odata=minimalmetadata;streaming=true;charset=utf-8
Location: https://media.windows.net/api/ContentKeys('nb%3Akid%3AUUID%3A9c8ea9c6-52bd-4232-8a43-8e43d8564a99')
Server: Microsoft-IIS/8.5
request-id: 76e85e0f-5cf1-44cb-b689-b3455888682c
x-ms-request-id: 76e85e0f-5cf1-44cb-b689-b3455888682c
X-Content-Type-Options: nosniff
DataServiceVersion: 3.0;
X-Powered-By: ASP.NET
Strict-Transport-Security: max-age=31536000; includeSubDomains
Date: Wed, 04 Feb 2015 02:37:46 GMT

{"odata.metadata":"https://wamsbayclus001rest-hs.cloudapp.net/api/$metadata#ContentKeys/@Element",
"Id":"nb:kid:UUID:9c8ea9c6-52bd-4232-8a43-8e43d8564a99","Created":"2015-02-04T02:37:46.9684379Z",
"LastModified":"2015-02-04T02:37:46.9684379Z",
"ContentKeyType":1,
"EncryptedContentKey":"your encrypted content key",
"Name":"ContentKey",
"ProtectionKeyId":"7D9BB04D9D0A4A24800CADBFEF232689E048F69C",
"ProtectionKeyType":0,
"Checksum":"calculated checksum"}

Associate the ContentKey with an Asset

After creating the ContentKey, associate it with your Asset using the $links operation, as shown in the following example:

Request:

POST https://media.windows.net/api/Assets('nb%3Acid%3AUUID%3Afbd7ce05-1087-401b-aaae-29f16383c801')/$links/ContentKeys HTTP/1.1
DataServiceVersion: 1.0;NetFx
MaxDataServiceVersion: 3.0;NetFx
Accept: application/json
Accept-Charset: UTF-8
Content-Type: application/json
Authorization: Bearer <ENCODED JWT TOKEN> 
x-ms-version: 2.17
Host: media.windows.net


{"uri":"https://wamsbayclus001rest-hs.cloudapp.net/api/ContentKeys('nb%3Akid%3AUUID%3A01e6ea36-2285-4562-91f1-82c45736047c')"}

Response:

HTTP/1.1 204 No Content 

Media Services learning paths

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