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

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);
    }
  }

}