Use AES-128 dynamic encryption and the key delivery service

Note

No new features or functionality are being added to Media Services v2.
Check out the latest version, Media Services v3. Also, see migration guidance from v2 to v3

You can use Media Services to deliver HTTP Live Streaming (HLS) and Smooth Streaming encrypted with the AES by using 128-bit encryption keys. Media Services also provides the key delivery service that delivers encryption keys to authorized users. If you want Media Services to encrypt an asset, you associate an encryption key with the asset and also configure authorization policies for the key. When a stream is requested by a player, Media Services uses the specified key to dynamically encrypt your content by using AES encryption. To decrypt the stream, the player requests the key from the key delivery service. To determine whether the user is authorized to get the key, the service evaluates the authorization policies that you specified for the key.

Media Services supports multiple ways of authenticating users who make key requests. The content key authorization policy can have one or more authorization restrictions, either open or token restrictions. The token-restricted policy must be accompanied by a token issued by a security token service (STS). Media Services supports tokens in the simple web token (SWT) and JSON Web Token (JWT) formats. For more information, see Configure the content key's authorization policy.

To take advantage of dynamic encryption, you need to have an asset that contains a set of multi-bitrate MP4 files or multi-bitrate Smooth Streaming source files. You also need to configure the delivery policy for the asset (described later in this article). Then, based on the format specified in the streaming URL, the on-demand streaming server ensures that the stream is delivered in the protocol you selected. As a result, you need to store and pay only for the files in single storage format. Media Services builds and serves the appropriate response based on requests from a client.

This article is useful to developers who work on applications that deliver protected media. The article shows you how to configure the key delivery service with authorization policies so that only authorized clients can receive encryption keys. It also shows how to use dynamic encryption.

For information on how to encrypt content with the Advanced Encryption Standard (AES) for delivery to Safari on macOS, see this blog post. For an overview of how to protect your media content with AES encryption, see this video.

AES-128 dynamic encryption and key delivery service workflow

Perform the following general steps when you encrypt your assets with AES by using the Media Services key delivery service and also by using dynamic encryption:

  1. Create an asset, and upload files into the asset.

  2. Encode the asset that contains the file to the adaptive bitrate MP4 set.

  3. Create a content key, and associate it with the encoded asset. In Media Services, the content key contains the asset's encryption key.

  4. Configure the content key's authorization policy. You must configure the content key authorization policy. The client must meet the policy before the content key is delivered to the client.

  5. Configure the delivery policy for an asset. The delivery policy configuration includes the key acquisition URL and an initialization vector (IV). (AES-128 requires the same IV for encryption and decryption.) The configuration also includes the delivery protocol (for example, MPEG-DASH, HLS, Smooth Streaming, or all) and the type of dynamic encryption (for example, envelope or no dynamic encryption).

    You can apply a different policy to each protocol on the same asset. For example, you can apply PlayReady encryption to Smooth/DASH and an AES envelope to HLS. Any protocols that aren't defined in a delivery policy are blocked from streaming. (An example is if you add a single policy that specifies only HLS as the protocol.) The exception is if you have no asset delivery policy defined at all. Then, all protocols are allowed in the clear.

  6. Create an OnDemand locator to get a streaming URL.

The article also shows how a client application can request a key from the key delivery service.

You can find a complete .NET example at the end of the article.

The following image demonstrates the workflow previously described. Here, the token is used for authentication.

Protect with AES-128

The remainder of this article provides explanations, code examples, and links to topics that show you how to achieve the tasks previously described.

Current limitations

If you add or update your asset's delivery policy, you must delete any existing locator and create a new locator.

Create an asset and upload files into the asset

To manage, encode, and stream your videos, you must first upload your content into Media Services. After it's uploaded, your content is stored securely in the cloud for further processing and streaming.

For more information, see Upload files into a Media Services account.

Encode the asset that contains the file to the adaptive bitrate MP4 set

With dynamic encryption, you create an asset that contains a set of multi-bitrate MP4 files or multi-bitrate Smooth Streaming source files. Then, based on the specified format in the manifest or fragment request, the on-demand streaming server ensures that you receive the stream in the protocol you selected. Then, you only need to store and pay for the files in single storage format. Media Services builds and serves the appropriate response based on requests from a client. For more information, see Dynamic packaging overview.

Note

When your Media Services account is created, a default streaming endpoint is added to your account in the "Stopped" state. To start streaming your content and take advantage of dynamic packaging and dynamic encryption, the streaming endpoint from which you want to stream content must be in the "Running" state.

Also, to use dynamic packaging and dynamic encryption, your asset must contain a set of adaptive bitrate MP4s or adaptive bitrate Smooth Streaming files.

For instructions on how to encode, see Encode an asset by using Media Encoder Standard.

Create a content key and associate it with the encoded asset

In Media Services, the content key contains the key that you want to encrypt an asset with.

For more information, see Create a content key.

Configure the content key's authorization policy

Media Services supports multiple ways of authenticating users who make key requests. You must configure the content key authorization policy. The client (player) must meet the policy before the key can be delivered to the client. The content key authorization policy can have one or more authorization restrictions, either open, token restriction, or IP restriction.

For more information, see Configure a content key authorization policy.

Configure an asset delivery policy

Configure the delivery policy for your asset. Some things that the asset delivery policy configuration includes are:

  • The key acquisition URL.
  • The initialization vector (IV) to use for the envelope encryption. AES-128 requires the same IV for encryption and decryption.
  • The asset delivery protocol (for example, MPEG-DASH, HLS, Smooth Streaming, or all).
  • The type of dynamic encryption (for example, AES envelope) or no dynamic encryption.

For more information, see Configure an asset delivery policy.

Create an OnDemand streaming locator to get a streaming URL

You need to provide your user with the streaming URL for Smooth Streaming, DASH, or HLS.

Note

If you add or update your asset's delivery policy, you must delete any existing locator and create a new locator.

For instructions on how to publish an asset and build a streaming URL, see Build a streaming URL.

Get a test token

Get a test token based on the token restriction that was used for the key authorization policy.

    // Deserializes a string containing an Xml representation of a TokenRestrictionTemplate
    // back into a TokenRestrictionTemplate class instance.
    TokenRestrictionTemplate tokenTemplate = 
        TokenRestrictionTemplateSerializer.Deserialize(tokenTemplateString);

    // Generate a test token based on the data in the given TokenRestrictionTemplate.
    //The GenerateTestToken method returns the token without the word "Bearer" in front
    //so you have to add it in front of the token string. 
    string testToken = TokenRestrictionTemplateSerializer.GenerateTestToken(tokenTemplate);
    Console.WriteLine("The authorization token is:\nBearer {0}", testToken);

You can use the Azure Media Services Player to test your stream.

How can your client request a key from the key delivery service?

In the previous step, you constructed the URL that points to a manifest file. Your client needs to extract the necessary information from the streaming manifest files to make a request to the key delivery service.

Manifest files

The client needs to extract the URL (that also contains content key ID [kid]) value from the manifest file. The client then tries to get the encryption key from the key delivery service. The client also needs to extract the IV value and use it to decrypt the stream. The following snippet shows the <Protection> element of the Smooth Streaming manifest:

    <Protection>
      <ProtectionHeader SystemID="B47B251A-2409-4B42-958E-08DBAE7B4EE9">
        <ContentProtection xmlns:sea="urn:mpeg:dash:schema:sea:2012" schemeIdUri="urn:mpeg:dash:sea:2012">
          <sea:SegmentEncryption schemeIdUri="urn:mpeg:dash:sea:aes128-cbc:2013"/>
          <sea:KeySystem keySystemUri="urn:mpeg:dash:sea:keysys:http:2013"/>
          <sea:CryptoPeriod IV="0xD7D7D7D7D7D7D7D7D7D7D7D7D7D7D7D7" 
                            keyUriTemplate="https://wamsbayclus001kd-hs.cloudapp.net/HlsHandler.ashx?
                                            kid=da3813af-55e6-48e7-aa9f-a4d6031f7b4d"/>
        </ContentProtection>
      </ProtectionHeader>
    </Protection>

In the case of HLS, the root manifest is broken into segment files.

For example, the root manifest is: http://test001.origin.mediaservices.windows.net/8bfe7d6f-34e3-4d1a-b289-3e48a8762490/BigBuckBunny.ism/manifest(format=m3u8-aapl). It contains a list of segment file names.

. . . 
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=630133,RESOLUTION=424x240,CODECS="avc1.4d4015,mp4a.40.2",AUDIO="audio"
QualityLevels(514369)/Manifest(video,format=m3u8-aapl)
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=965441,RESOLUTION=636x356,CODECS="avc1.4d401e,mp4a.40.2",AUDIO="audio"
QualityLevels(842459)/Manifest(video,format=m3u8-aapl)
…

If you open one of the segment files in a text editor (for example, http://test001.origin.mediaservices.windows.net/8bfe7d6f-34e3-4d1a-b289-3e48a8762490/BigBuckBunny.ism/QualityLevels(514369)/Manifest(video,format=m3u8-aapl), it contains #EXT-X-KEY, which indicates that the file is encrypted.

#EXTM3U
#EXT-X-VERSION:4
#EXT-X-ALLOW-CACHE:NO
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-TARGETDURATION:9
#EXT-X-KEY:METHOD=AES-128,
URI="https://wamsbayclus001kd-hs.cloudapp.net/HlsHandler.ashx?
     kid=da3813af-55e6-48e7-aa9f-a4d6031f7b4d",
        IV=0XD7D7D7D7D7D7D7D7D7D7D7D7D7D7D7D7
#EXT-X-PROGRAM-DATE-TIME:1970-01-01T00:00:00.000+00:00
#EXTINF:8.425708,no-desc
Fragments(video=0,format=m3u8-aapl)
#EXT-X-ENDLIST

Note

If you plan to play an AES-encrypted HLS in Safari, see this blog.

Request the key from the key delivery service

The following code shows how to send a request to the Media Services key delivery service by using a key delivery Uri (that was extracted from the manifest) and a token. (This article doesn't explain how to get SWTs from an STS.)

    private byte[] GetDeliveryKey(Uri keyDeliveryUri, string token)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(keyDeliveryUri);

        request.Method = "POST";
        request.ContentType = "text/xml";
        if (!string.IsNullOrEmpty(token))
        {
            request.Headers[AuthorizationHeader] = token;
        }
        request.ContentLength = 0;

        var response = request.GetResponse();

        var stream = response.GetResponseStream();
        if (stream == null)
        {
            throw new NullReferenceException("Response stream is null");
        }

        var buffer = new byte[256];
        var length = 0;
        while (stream.CanRead && length <= buffer.Length)
        {
            var nexByte = stream.ReadByte();
            if (nexByte == -1)
            {
                break;
            }
            buffer[length] = (byte)nexByte;
            length++;
        }
        response.Close();

        // AES keys must be exactly 16 bytes (128 bits).
        var key = new byte[length];
        Array.Copy(buffer, key, length);
        return key;
    }

Protect your content with AES-128 by using .NET

Create and configure a Visual Studio project

  1. Set up your development environment, and populate the app.config file with connection information, as described in Media Services development with .NET.

  2. Add the following elements to appSettings, as defined in your app.config file:

    <add key="Issuer" value="http://testissuer.com"/>
    <add key="Audience" value="urn:test"/>
    

Example

Overwrite the code in your Program.cs file with the code shown in this section.

Note

There is a limit of 1,000,000 policies for different Media Services policies (for example, for Locator policy or ContentKeyAuthorizationPolicy). Use the same policy ID if you always use the same days/access permissions. An example is policies for locators that are intended to remain in place for a long time (non-upload policies). For more information, see the "Limit access policies" section in Manage assets and related entities with the Media Services .NET SDK.

Make sure to update variables to point to folders where your input files are located.

using System;
using System.Collections.Generic;
using System.Configuration;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using Microsoft.WindowsAzure.MediaServices.Client;
using System.Threading;
using Microsoft.WindowsAzure.MediaServices.Client.ContentKeyAuthorization;
using Microsoft.WindowsAzure.MediaServices.Client.DynamicEncryption;

namespace DynamicEncryptionWithAES
{
    class Program
    {
        // Read values from the App.config file.
        static string _AADTenantDomain =
            ConfigurationManager.AppSettings["AMSAADTenantDomain"];
        static string _RESTAPIEndpoint =
            ConfigurationManager.AppSettings["AMSRESTAPIEndpoint"];
        static string _AMSClientId =
            ConfigurationManager.AppSettings["AMSClientId"];
        static string _AMSClientSecret =
            ConfigurationManager.AppSettings["AMSClientSecret"];

        // A Uri describing the issuer of the token.  
        // Must match the value in the token for the token to be considered valid.
        private static readonly Uri _sampleIssuer =
            new Uri(ConfigurationManager.AppSettings["Issuer"]);
        // The Audience or Scope of the token.  
        // Must match the value in the token for the token to be considered valid.
        private static readonly Uri _sampleAudience =
            new Uri(ConfigurationManager.AppSettings["Audience"]);

        // Field for service context.
        private static CloudMediaContext _context = null;

        private static readonly string _mediaFiles =
            Path.GetFullPath(@"../..\Media");

        private static readonly string _singleMP4File =
            Path.Combine(_mediaFiles, @"BigBuckBunny.mp4");

        static void Main(string[] args)
        {
            AzureAdTokenCredentials tokenCredentials =
                new AzureAdTokenCredentials(_AADTenantDomain,
                    new AzureAdClientSymmetricKey(_AMSClientId, _AMSClientSecret),
                    AzureEnvironments.AzureCloudEnvironment);

            var tokenProvider = new AzureAdTokenProvider(tokenCredentials);

            _context = new CloudMediaContext(new Uri(_RESTAPIEndpoint), tokenProvider);
            
            bool tokenRestriction = true;
            string tokenTemplateString = null;

            IAsset asset = UploadFileAndCreateAsset(_singleMP4File);
            Console.WriteLine("Uploaded asset: {0}", asset.Id);

            IAsset encodedAsset = EncodeToAdaptiveBitrateMP4Set(asset);
            Console.WriteLine("Encoded asset: {0}", encodedAsset.Id);

            IContentKey key = CreateEnvelopeTypeContentKey(encodedAsset);
            Console.WriteLine("Created key {0} for the asset {1} ", key.Id, encodedAsset.Id);
            Console.WriteLine();

            if (tokenRestriction)
                tokenTemplateString = AddTokenRestrictedAuthorizationPolicy(key);
            else
                AddOpenAuthorizationPolicy(key);

            Console.WriteLine("Added authorization policy: {0}", key.AuthorizationPolicyId);
            Console.WriteLine();

            CreateAssetDeliveryPolicy(encodedAsset, key);
            Console.WriteLine("Created asset delivery policy. \n");
            Console.WriteLine();

            if (tokenRestriction && !String.IsNullOrEmpty(tokenTemplateString))
            {
                // Deserializes a string containing an Xml representation of a TokenRestrictionTemplate
                // back into a TokenRestrictionTemplate class instance.
                TokenRestrictionTemplate tokenTemplate =
                    TokenRestrictionTemplateSerializer.Deserialize(tokenTemplateString);

                // Generate a test token based on the data in the given TokenRestrictionTemplate.
                // Note, you need to pass the key id Guid because we specified 
                // TokenClaim.ContentKeyIdentifierClaim in during the creation of TokenRestrictionTemplate.
                Guid rawkey = EncryptionUtils.GetKeyIdAsGuid(key.Id);

                //The GenerateTestToken method returns the token without the word “Bearer” in front
                //so you have to add it in front of the token string. 
                string testToken = TokenRestrictionTemplateSerializer.GenerateTestToken(tokenTemplate, null, rawkey, DateTime.UtcNow.AddDays(365));

                Console.WriteLine("The authorization token is:\nBearer {0}", testToken);
                Console.WriteLine();
            }

            // You can use the bit.ly/aesplayer Flash player to test the URL 
            // (with open authorization policy). 
            // Paste the URL and click the Update button to play the video. 
            //
            string URL = GetStreamingOriginLocator(encodedAsset);
            Console.WriteLine("Smooth Streaming Url: {0}/manifest", URL);
            Console.WriteLine();
            Console.WriteLine("HLS Url: {0}/manifest(format=m3u8-aapl)", URL);
            Console.WriteLine();

            Console.ReadLine();
        }

        static public IAsset UploadFileAndCreateAsset(string singleFilePath)
        {
            if (!File.Exists(singleFilePath))
            {
                Console.WriteLine("File does not exist.");
                return null;
            }

            var assetName = Path.GetFileNameWithoutExtension(singleFilePath);
            IAsset inputAsset = _context.Assets.Create(assetName, AssetCreationOptions.StorageEncrypted);

            var assetFile = inputAsset.AssetFiles.Create(Path.GetFileName(singleFilePath));

            Console.WriteLine("Created assetFile {0}", assetFile.Name);

            var policy = _context.AccessPolicies.Create(
                                    assetName,
                                    TimeSpan.FromDays(30),
                                    AccessPermissions.Write | AccessPermissions.List);

            var locator = _context.Locators.CreateLocator(LocatorType.Sas, inputAsset, policy);

            Console.WriteLine("Upload {0}", assetFile.Name);

            assetFile.Upload(singleFilePath);
            Console.WriteLine("Done uploading {0}", assetFile.Name);

            locator.Delete();
            policy.Delete();

            return inputAsset;
        }

        static public IAsset EncodeToAdaptiveBitrateMP4Set(IAsset asset)
        {
            // Declare a new job.
            IJob job = _context.Jobs.Create("Media Encoder Standard Job");
            // Get a media processor reference, and pass to it the name of the 
            // processor to use for the specific task.
            IMediaProcessor processor = GetLatestMediaProcessorByName("Media Encoder Standard");

            // Create a task with the encoding details, using a string preset.
            // In this case "H264 Multiple Bitrate 720p" preset is used.
            ITask task = job.Tasks.AddNew("My encoding task",
                processor,
                "H264 Multiple Bitrate 720p",
                TaskOptions.None);

            // Specify the input asset to be encoded.
            task.InputAssets.Add(asset);
            // Add an output asset to contain the results of the job. 
            // This output is specified as AssetCreationOptions.None, which 
            // means the output asset is not encrypted. 
            task.OutputAssets.AddNew("Output asset",
                AssetCreationOptions.None);

            job.StateChanged += new EventHandler<JobStateChangedEventArgs>(JobStateChanged);
            job.Submit();
            job.GetExecutionProgressTask(CancellationToken.None).Wait();

            return job.OutputMediaAssets[0];
        }

        private static IMediaProcessor GetLatestMediaProcessorByName(string mediaProcessorName)
        {
            var processor = _context.MediaProcessors.Where(p => p.Name == mediaProcessorName).
            ToList().OrderBy(p => new Version(p.Version)).LastOrDefault();

            if (processor == null)
                throw new ArgumentException(string.Format("Unknown media processor", mediaProcessorName));

            return processor;
        }

        static public IContentKey CreateEnvelopeTypeContentKey(IAsset asset)
        {
            // Create envelope encryption content key
            Guid keyId = Guid.NewGuid();
            byte[] contentKey = GetRandomBuffer(16);

            IContentKey key = _context.ContentKeys.Create(
                                    keyId,
                                    contentKey,
                                    "ContentKey",
                                    ContentKeyType.EnvelopeEncryption);

            // Associate the key with the asset.
            asset.ContentKeys.Add(key);

            return key;
        }

        static public void AddOpenAuthorizationPolicy(IContentKey contentKey)
        {
            // Create ContentKeyAuthorizationPolicy with Open restrictions 
            // and create authorization policy             
            IContentKeyAuthorizationPolicy policy = _context.
                                    ContentKeyAuthorizationPolicies.
                                    CreateAsync("Open Authorization Policy").Result;

            List<ContentKeyAuthorizationPolicyRestriction> restrictions =
                new List<ContentKeyAuthorizationPolicyRestriction>();

            ContentKeyAuthorizationPolicyRestriction restriction =
                new ContentKeyAuthorizationPolicyRestriction
                {
                    Name = "HLS Open Authorization Policy",
                    KeyRestrictionType = (int)ContentKeyRestrictionType.Open,
                    Requirements = null // no requirements needed for HLS
                };

            restrictions.Add(restriction);

            IContentKeyAuthorizationPolicyOption policyOption =
                _context.ContentKeyAuthorizationPolicyOptions.Create(
                "policy",
                ContentKeyDeliveryType.BaselineHttp,
                restrictions,
                "");

            policy.Options.Add(policyOption);

            // Add ContentKeyAutorizationPolicy to ContentKey
            contentKey.AuthorizationPolicyId = policy.Id;
            IContentKey updatedKey = contentKey.UpdateAsync().Result;
            Console.WriteLine("Adding Key to Asset: Key ID is " + updatedKey.Id);
        }

        public static string AddTokenRestrictedAuthorizationPolicy(IContentKey contentKey)
        {
            string tokenTemplateString = GenerateTokenRequirements();

            IContentKeyAuthorizationPolicy policy = _context.
                                    ContentKeyAuthorizationPolicies.
                                    CreateAsync("HLS token restricted authorization policy").Result;

            List<ContentKeyAuthorizationPolicyRestriction> restrictions =
                    new List<ContentKeyAuthorizationPolicyRestriction>();

            ContentKeyAuthorizationPolicyRestriction restriction =
                    new ContentKeyAuthorizationPolicyRestriction
                    {
                        Name = "Token Authorization Policy",
                        KeyRestrictionType = (int)ContentKeyRestrictionType.TokenRestricted,
                        Requirements = tokenTemplateString
                    };

            restrictions.Add(restriction);

            //You could have multiple options 
            IContentKeyAuthorizationPolicyOption policyOption =
                _context.ContentKeyAuthorizationPolicyOptions.Create(
                    "Token option for HLS",
                    ContentKeyDeliveryType.BaselineHttp,
                    restrictions,
                    null  // no key delivery data is needed for HLS
                    );

            policy.Options.Add(policyOption);

            // Add ContentKeyAutorizationPolicy to ContentKey
            contentKey.AuthorizationPolicyId = policy.Id;
            IContentKey updatedKey = contentKey.UpdateAsync().Result;
            Console.WriteLine("Adding Key to Asset: Key ID is " + updatedKey.Id);

            return tokenTemplateString;
        }

        static public void CreateAssetDeliveryPolicy(IAsset asset, IContentKey key)
        {
            Uri keyAcquisitionUri = key.GetKeyDeliveryUrl(ContentKeyDeliveryType.BaselineHttp);

            string envelopeEncryptionIV = Convert.ToBase64String(GetRandomBuffer(16));

            // The following policy configuration specifies: 
            //   key url that will have KID=<Guid> appended to the envelope and
            //   the Initialization Vector (IV) to use for the envelope encryption.
            Dictionary<AssetDeliveryPolicyConfigurationKey, string> assetDeliveryPolicyConfiguration =
                new Dictionary<AssetDeliveryPolicyConfigurationKey, string>
            {
                        {AssetDeliveryPolicyConfigurationKey.EnvelopeKeyAcquisitionUrl, keyAcquisitionUri.ToString()}
            };

            IAssetDeliveryPolicy assetDeliveryPolicy =
                _context.AssetDeliveryPolicies.Create(
                            "AssetDeliveryPolicy",
                            AssetDeliveryPolicyType.DynamicEnvelopeEncryption,
                            AssetDeliveryProtocol.SmoothStreaming | AssetDeliveryProtocol.HLS | AssetDeliveryProtocol.Dash,
                            assetDeliveryPolicyConfiguration);

            // Add AssetDelivery Policy to the asset
            asset.DeliveryPolicies.Add(assetDeliveryPolicy);
            Console.WriteLine();
            Console.WriteLine("Adding Asset Delivery Policy: " +
                assetDeliveryPolicy.AssetDeliveryPolicyType);
        }

        static public string GetStreamingOriginLocator(IAsset asset)
        {

            // Get a reference to the streaming manifest file from the  
            // collection of files in the asset. 

            var assetFile = asset.AssetFiles.ToList().Where(f => f.Name.ToLower().
                                        EndsWith(".ism")).
                                        FirstOrDefault();

            // Create a 30-day readonly access policy. 
            // You cannot create a streaming locator using an AccessPolicy that includes write or delete permissions.            
            IAccessPolicy policy = _context.AccessPolicies.Create("Streaming policy",
                TimeSpan.FromDays(30),
                AccessPermissions.Read);

            // Create a locator to the streaming content on an origin. 
            ILocator originLocator = _context.Locators.CreateLocator(LocatorType.OnDemandOrigin, asset,
                policy,
                DateTime.UtcNow.AddMinutes(-5));

            // Create a URL to the manifest file. 
            return originLocator.Path + assetFile.Name;
        }

        static private string GenerateTokenRequirements()
        {
            TokenRestrictionTemplate template = new TokenRestrictionTemplate(TokenType.SWT);

            template.PrimaryVerificationKey = new SymmetricVerificationKey();
            template.AlternateVerificationKeys.Add(new SymmetricVerificationKey());
            template.Audience = _sampleAudience.ToString();
            template.Issuer = _sampleIssuer.ToString();

            template.RequiredClaims.Add(TokenClaim.ContentKeyIdentifierClaim);

            return TokenRestrictionTemplateSerializer.Serialize(template);
        }

        static private void JobStateChanged(object sender, JobStateChangedEventArgs e)
        {
            Console.WriteLine(string.Format("{0}\n  State: {1}\n  Time: {2}\n\n",
                ((IJob)sender).Name,
                e.CurrentState,
                DateTime.UtcNow.ToString(@"yyyy_M_d__hh_mm_ss")));
        }

        static private byte[] GetRandomBuffer(int size)
        {
            byte[] randomBytes = new byte[size];
            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
            {
                rng.GetBytes(randomBytes);
            }

            return randomBytes;
        }
    }
}

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