Using AWS KMS keys for Amazon S3 encryption in the AWS SDK for .NET - AWS SDK for .NET
Create encryption materialsCreate and encrypt an Amazon S3 objectComplete codeAdditional considerations

Using AWS KMS keys for Amazon S3 encryption in the AWS SDK for .NET

This example shows you how to use AWS Key Management Service keys to encrypt Amazon S3 objects. The application creates a customer master key (CMK) and uses it to create an AmazonS3EncryptionClientV2 object for client-side encryption. The application uses that client to create an encrypted object from a given text file in an existing Amazon S3 bucket. It then decrypts the object and displays its contents.

Warning

A similar class called AmazonS3EncryptionClient is deprecated and is less secure than the AmazonS3EncryptionClientV2 class. To migrate existing code that uses AmazonS3EncryptionClient, see S3 Encryption Client Migration.

Create encryption materials

The following snippet creates an EncryptionMaterials object that contains a KMS key ID.

The example at the end of this topic shows this snippet in use.

      // Create a customer master key (CMK) and store the result
      CreateKeyResponse createKeyResponse =
        await new AmazonKeyManagementServiceClient().CreateKeyAsync(new CreateKeyRequest());
      var kmsEncryptionContext = new Dictionary<string, string>();
      var kmsEncryptionMaterials = new EncryptionMaterialsV2(
        createKeyResponse.KeyMetadata.KeyId, KmsType.KmsContext, kmsEncryptionContext);

Create and encrypt an Amazon S3 object

The following snippet creates an AmazonS3EncryptionClientV2 object that uses the encryption materials created earlier. It then uses the client to create and encrypt a new Amazon S3 object.

The example at the end of this topic shows this snippet in use.

    //
    // Method to create and encrypt an object in an S3 bucket
    static async Task<GetObjectResponse> CreateAndRetrieveObjectAsync(
      EncryptionMaterialsV2 materials, string bucketName,
      string fileName, string itemName)
    {
      // CryptoStorageMode.ObjectMetadata is required for KMS EncryptionMaterials
      var config = new AmazonS3CryptoConfigurationV2(SecurityProfile.V2AndLegacy)
      {
        StorageMode = CryptoStorageMode.ObjectMetadata
      };
      var s3EncClient = new AmazonS3EncryptionClientV2(config, materials);

      // Create, encrypt, and put the object
      await s3EncClient.PutObjectAsync(new PutObjectRequest
      {
        BucketName = bucketName,
        Key = itemName,
        ContentBody = File.ReadAllText(fileName)
      });

      // Get, decrypt, and return the object
      return await s3EncClient.GetObjectAsync(new GetObjectRequest
      {
        BucketName = bucketName,
        Key = itemName
      });
    }

Complete code

This section shows relevant references and the complete code for this example.

NuGet packages:

Programming elements:

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading.Tasks;
using Amazon.Extensions.S3.Encryption;
using Amazon.Extensions.S3.Encryption.Primitives;
using Amazon.S3.Model;
using Amazon.KeyManagementService;
using Amazon.KeyManagementService.Model;

namespace KmsS3Encryption
{
  // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  // Class to store text in an encrypted S3 object.
  class Program
  {
    private const int MaxArgs = 3;

    public static async Task Main(string[] args)
    {
      // Parse the command line and show help if necessary
      var parsedArgs = CommandLine.Parse(args);
      if((parsedArgs.Count == 0) || (parsedArgs.Count > MaxArgs))
      {
        PrintHelp();
        return;
      }

      // Get the application arguments from the parsed list
      string bucketName =
        CommandLine.GetArgument(parsedArgs, null, "-b", "--bucket-name");
      string fileName =
        CommandLine.GetArgument(parsedArgs, null, "-f", "--file-name");
      string itemName =
        CommandLine.GetArgument(parsedArgs, null, "-i", "--item-name");
      if(string.IsNullOrEmpty(bucketName) || (string.IsNullOrEmpty(fileName)))
        CommandLine.ErrorExit(
          "\nOne or more of the required arguments is missing or incorrect." +
          "\nRun the command with no arguments to see help.");
      if(!File.Exists(fileName))
        CommandLine.ErrorExit($"\nThe given file {fileName} doesn't exist.");
      if(string.IsNullOrEmpty(itemName))
        itemName = Path.GetFileName(fileName);

      // Create a customer master key (CMK) and store the result
      CreateKeyResponse createKeyResponse =
        await new AmazonKeyManagementServiceClient().CreateKeyAsync(new CreateKeyRequest());
      var kmsEncryptionContext = new Dictionary<string, string>();
      var kmsEncryptionMaterials = new EncryptionMaterialsV2(
        createKeyResponse.KeyMetadata.KeyId, KmsType.KmsContext, kmsEncryptionContext);

      // Create the object in the bucket, then display the content of the object
      var putObjectResponse =
        await CreateAndRetrieveObjectAsync(kmsEncryptionMaterials, bucketName, fileName, itemName);
      Stream stream = putObjectResponse.ResponseStream;
      StreamReader reader = new StreamReader(stream);
      Console.WriteLine(reader.ReadToEnd());
    }


    //
    // Method to create and encrypt an object in an S3 bucket
    static async Task<GetObjectResponse> CreateAndRetrieveObjectAsync(
      EncryptionMaterialsV2 materials, string bucketName,
      string fileName, string itemName)
    {
      // CryptoStorageMode.ObjectMetadata is required for KMS EncryptionMaterials
      var config = new AmazonS3CryptoConfigurationV2(SecurityProfile.V2AndLegacy)
      {
        StorageMode = CryptoStorageMode.ObjectMetadata
      };
      var s3EncClient = new AmazonS3EncryptionClientV2(config, materials);

      // Create, encrypt, and put the object
      await s3EncClient.PutObjectAsync(new PutObjectRequest
      {
        BucketName = bucketName,
        Key = itemName,
        ContentBody = File.ReadAllText(fileName)
      });

      // Get, decrypt, and return the object
      return await s3EncClient.GetObjectAsync(new GetObjectRequest
      {
        BucketName = bucketName,
        Key = itemName
      });
    }


    //
    // Command-line help
    private static void PrintHelp()
    {
      Console.WriteLine(
        "\nUsage: KmsS3Encryption -b <bucket-name> -f <file-name> [-i <item-name>]" +
        "\n  -b, --bucket-name: The name of an existing S3 bucket." +
        "\n  -f, --file-name: The name of a text file with content to encrypt and store in S3." +
        "\n  -i, --item-name: The name you want to use for the item." +
        "\n      If item-name isn't given, file-name will be used.");
    }

  }

  // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  // Class that represents a command line on the console or terminal.
  // (This is the same for all examples. When you have seen it once, you can ignore it.)
  static class CommandLine
  {
    //
    // Method to parse a command line of the form: "--key value" or "-k value".
    //
    // Parameters:
    // - args: The command-line arguments passed into the application by the system.
    //
    // Returns:
    // A Dictionary with string Keys and Values.
    //
    // If a key is found without a matching value, Dictionary.Value is set to the key
    //  (including the dashes).
    // If a value is found without a matching key, Dictionary.Key is set to "--NoKeyN",
    //  where "N" represents sequential numbers.
    public static Dictionary<string,string> Parse(string[] args)
    {
      var parsedArgs = new Dictionary<string,string>();
      int i = 0, n = 0;
      while(i < args.Length)
      {
        // If the first argument in this iteration starts with a dash it's an option.
        if(args[i].StartsWith("-"))
        {
          var key = args[i++];
          var value = key;

          // Check to see if there's a value that goes with this option?
          if((i < args.Length) && (!args[i].StartsWith("-"))) value = args[i++];
          parsedArgs.Add(key, value);
        }

        // If the first argument in this iteration doesn't start with a dash, it's a value
        else
        {
          parsedArgs.Add("--NoKey" + n.ToString(), args[i++]);
          n++;
        }
      }

      return parsedArgs;
    }

    //
    // Method to get an argument from the parsed command-line arguments
    //
    // Parameters:
    // - parsedArgs: The Dictionary object returned from the Parse() method (shown above).
    // - defaultValue: The default string to return if the specified key isn't in parsedArgs.
    // - keys: An array of keys to look for in parsedArgs.
    public static string GetArgument(
      Dictionary<string,string> parsedArgs, string defaultReturn, params string[] keys)
    {
      string retval = null;
      foreach(var key in keys)
        if(parsedArgs.TryGetValue(key, out retval)) break;
      return retval ?? defaultReturn;
    }

    //
    // Method to exit the application with an error.
    public static void ErrorExit(string msg, int code=1)
    {
      Console.WriteLine("\nError");
      Console.WriteLine(msg);
      Environment.Exit(code);
    }
  }

}

Additional considerations

  • You can check the results of this example. To do so, go to the Amazon S3 console and open the bucket you provided to the application. Then find the new object, download it, and open it in a text editor.

  • The AmazonS3EncryptionClientV2 class implements the same interface as the standard AmazonS3Client class. This makes it easier to port your code to the AmazonS3EncryptionClientV2 class so that encryption and decryption happen automatically and transparently in the client.

  • One advantage of using an AWS KMS key as your master key is that you don't need to store and manage your own master keys; this is done by AWS. A second advantage is that the AmazonS3EncryptionClientV2 class of the AWS SDK for .NET is interoperable with the AmazonS3EncryptionClientV2 class of the AWS SDK for Java. This means you can encrypt with the AWS SDK for Java and decrypt with the AWS SDK for .NET, and vice versa.

    Note

    The AmazonS3EncryptionClientV2 class of the AWS SDK for .NET supports KMS master keys only when run in metadata mode. The instruction file mode of the AmazonS3EncryptionClientV2 class of the AWS SDK for .NET is incompatible with the AmazonS3EncryptionClientV2 class of the AWS SDK for Java.