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Use Automatic Client-Side Field Level Encryption with Azure

Overview

This guide shows you how to build a Client-Side Field Level Encryption (CSFLE)-enabled application using Azure Key Vault.

After you complete the steps in this guide, you should have:

  • A Customer Master Key hosted on an Azure Key Vault instance.

  • A working client application that inserts documents with encrypted fields using your Customer Master Key.

Before You Get Started

To complete and run the code in this guide, you need to set up your development environment as shown in the Installation Requirements page.

Throughout this guide, code examples use placeholder text. Before you run the examples, substitute your own values for these placeholders.

For example:

dek_id := "<Your Base64 DEK ID>"

You would replace everything between quotes with your DEK ID.

dek_id := "abc123"

Select the programming language for which you want to see code examples for from the Select your language dropdown menu on the right side of the page.

Tip

See: Full Application

To view the complete runnable application code for this tutorial, go to the following link:

Set Up the KMS

// You are viewing the .NET/C# driver code examples.
// Use the dropdown menu to select a different driver.
1

Register your Application with Azure

Log in to Azure.
Register your Application with Azure Active Directory

To register an application on Azure Active Directory, follow Microsoft's official Register an application with the Microsoft identity platform Quick Start.

Important

Record your Credentials

Ensure you record the following credentials:

  • Tenant ID

  • Client ID

  • Client secret

You need these credentials to construct your kmsProviders object later in this tutorial. You can also authenticate by using an access token or automatic credential fetching. To learn about all available credential forms for Azure, see kmsProviders Object.

2

Create the Customer Master Key

Create your Azure Key Vault and Customer Master Key

To create a new Azure Key Vault instance and Customer Master Key, follow Microsoft's official Set and retrieve a key from Azure Key Vault using the Azure portal Quick Start.

Note

The Customer Master Key should have an RSA key size of 2048 or 4096 bits.

Important

Record your Credentials

Ensure you record the following credentials:

  • Key Name

  • Key Identifier (referred to as keyVaultEndpoint later in this guide)

  • Key Version

You will need them to construct your dataKeyOpts object later in this tutorial.

Grant Permissions

Grant your client application wrap and unwrap permissions to the key.

Create the Application

1

Create a Unique Index on your Key Vault collection

Create a unique index on the keyAltNames field in your encryption.__keyVault namespace.

Select the tab corresponding to your preferred MongoDB driver:

var connectionString = "<Your MongoDB URI>";
var keyVaultNamespace = CollectionNamespace.FromFullName("encryption.__keyVault");
var keyVaultClient = new MongoClient(connectionString);
var indexOptions = new CreateIndexOptions<BsonDocument>();
indexOptions.Unique = true;
indexOptions.PartialFilterExpression = new BsonDocument { { "keyAltNames", new BsonDocument { { "$exists", new BsonBoolean(true) } } } };
var builder = Builders<BsonDocument>.IndexKeys;
var indexKeysDocument = builder.Ascending("keyAltNames");
var indexModel = new CreateIndexModel<BsonDocument>(indexKeysDocument, indexOptions);
var keyVaultDatabase = keyVaultClient.GetDatabase(keyVaultNamespace.DatabaseNamespace.ToString());
// Drop the Key Vault Collection in case you created this collection
// in a previous run of this application.  
keyVaultDatabase.DropCollection(keyVaultNamespace.CollectionName);
// Drop the database storing your encrypted fields as all
// the DEKs encrypting those fields were deleted in the preceding line.
keyVaultClient.GetDatabase("medicalRecords").DropCollection("patients");
var keyVaultCollection = keyVaultDatabase.GetCollection<BsonDocument>(keyVaultNamespace.CollectionName.ToString());
keyVaultCollection.Indexes.CreateOne(indexModel);
2

Create a New Data Encryption Key

Add your Azure Key Vault Credentials

Add the service account credentials to your CSFLE-enabled client code.

var kmsProviders = new Dictionary<string, IReadOnlyDictionary<string, object>>();
var provider = "azure";
var azureKmsOptions = new Dictionary<string, object>
{
   { "tenantId", "<Your Azure Tenant ID>" },
   { "clientId", "<Your Azure Client ID>" },
   { "clientSecret", "<Your Azure Client Secret>" },
};
Add Your Key Information

Update the following code to specify your Customer Master Key:

Tip

You recorded your Customer Master Key's ARN and Region in the Create a Customer Master Key step of this guide.

kmsProviders.Add(provider, azureKmsOptions);
var dataKeyOptions = new DataKeyOptions(
masterKey: new BsonDocument
{
   { "keyName", "<Your Azure Key Name>" },
   { "keyVaultEndpoint", "<Your Azure Key Vault Endpoint>" },
});
Generate your Data Encryption Key

Generate your Data Encryption Key using the variables declared in step one of this tutorial.

var clientEncryptionOptions = new ClientEncryptionOptions(
    keyVaultClient: keyVaultClient,
    keyVaultNamespace: keyVaultNamespace,
    kmsProviders: kmsProviders
    );
var clientEncryption = new ClientEncryption(clientEncryptionOptions);
var dataKeyId = clientEncryption.CreateDataKey(provider, dataKeyOptions, CancellationToken.None);
var dataKeyIdBase64 = Convert.ToBase64String(GuidConverter.ToBytes(dataKeyId, GuidRepresentation.Standard));
Console.WriteLine($"DataKeyId [base64]: {dataKeyIdBase64}");

Tip

Learn More

To view a diagram showing how your client application creates your Data Encryption Key when using an Azure Key Vault, see Architecture.

To learn more about the options for creating a Data Encryption Key encrypted with a Customer Master Key hosted in Azure Key Vault, see kmsProviders Object and dataKeyOpts Object.

Tip

See: Complete Code

To view the complete code for making a Data Encryption Key, see our Github repository

3

Configure the MongoClient

Tip

Follow the remaining steps in this tutorial in a separate file from the one created in the previous steps.

To view the complete code for this file, see our Github repository

Specify the Key Vault Collection Namespace

Specify encryption.__keyVault as the Key Vault collection namespace.

var keyVaultNamespace = CollectionNamespace.FromFullName("encryption.__keyVault");
Specify your Azure Credentials

Specify the azure KMS provider and your Azure credentials:

var kmsProviders = new Dictionary<string, IReadOnlyDictionary<string, object>>();
var provider = "azure";
var azureKmsOptions = new Dictionary<string, object>
{
   { "tenantId", "<Your Azure Tenant ID>" },
   { "clientId", "<Your Azure Client ID>" },
   { "clientSecret", "<Your Azure Client Secret>" },
};
kmsProviders.Add(provider, azureKmsOptions);
Create an Encryption Schema For Your Collection

Tip

Add Your Data Encryption Key Base64 ID

Make sure to update the following code to include your Base64 DEK ID. You received this value in the Generate your Data Encryption Key step of this guide.

var keyId = "<Your base64 DEK ID here>";
var schema = new BsonDocument
{
   { "bsonType", "object" },
   {
       "encryptMetadata",
       new BsonDocument("keyId", new BsonArray(new[] { new BsonBinaryData(Convert.FromBase64String(keyId), BsonBinarySubType.UuidStandard) }))
   },
   {
       "properties",
       new BsonDocument
       {
           {
               "ssn", new BsonDocument
               {
                   {
                       "encrypt", new BsonDocument
                       {
                           { "bsonType", "int" },
                           { "algorithm", "AEAD_AES_256_CBC_HMAC_SHA_512-Deterministic" }
                       }
                   }
               }
           },
           {
               "bloodType", new BsonDocument
               {
                   {
                       "encrypt", new BsonDocument
                       {
                           { "bsonType", "string" },
                           { "algorithm", "AEAD_AES_256_CBC_HMAC_SHA_512-Random" }
                       }
                   }
               }
           },
           {
               "medicalRecords", new BsonDocument
               {
                   {
                       "encrypt", new BsonDocument
                       {
                           { "bsonType", "array" },
                           { "algorithm", "AEAD_AES_256_CBC_HMAC_SHA_512-Random" }
                       }
                   }
               }
           },
           {
               "insurance", new BsonDocument
               {
                   { "bsonType", "object" },
                   {
                       "properties", new BsonDocument
                       {
                           {
                               "policyNumber", new BsonDocument
                               {
                                   {
                                       "encrypt", new BsonDocument
                                       {
                                           { "bsonType", "int" },
                                           { "algorithm", "AEAD_AES_256_CBC_HMAC_SHA_512-Deterministic" }
                                       }
                                   }
                               }
                           }
                       }
                   }
               }
           }
       }
   }
};
var schemaMap = new Dictionary<string, BsonDocument>();
schemaMap.Add(dbNamespace, schema);
Specify the Location of the Automatic Encryption Shared Library
var mongoBinariesPath = "<Full path to your Automatic Encryption Shared Library>";
var extraOptions = new Dictionary<string, object>()
{
   { "cryptSharedLibPath", mongoBinariesPath },
};

Note

Automatic Encryption Options

The automatic encryption options provide configuration information to the Automatic Encryption Shared Library, which modifies the application's behavior when accessing encrypted fields.

To learn more about the Automatic Encryption Shared Library, see the Automatic Encryption Shared Library for CSFLE page.

Create the MongoClient

Instantiate a MongoDB client object with the following automatic encryption settings that use the variables declared in the previous steps:

var clientSettings = MongoClientSettings.FromConnectionString(connectionString);
var autoEncryptionOptions = new AutoEncryptionOptions(
    keyVaultNamespace: keyVaultNamespace,
    kmsProviders: kmsProviders,
    schemaMap: schemaMap,
    extraOptions: extraOptions
    );
clientSettings.AutoEncryptionOptions = autoEncryptionOptions;
var secureClient = new MongoClient(clientSettings);
4

Insert a Document with Encrypted Fields

Use your CSFLE-enabled MongoClient instance to insert a document with encrypted fields into the medicalRecords.patients namespace using the following code snippet:

var sampleDocFields = new BsonDocument
{
    { "name", "Jon Doe" },
    { "ssn", 145014000 },
    { "bloodType", "AB-" },
    {
        "medicalRecords", new BsonArray
        {
            new BsonDocument("weight", 180),
            new BsonDocument("bloodPressure", "120/80")
        }
    },
    {
        "insurance", new BsonDocument
        {
            { "policyNumber", 123142 },
            { "provider", "MaestCare" }
        }
    }
};
// Construct an auto-encrypting client
var secureCollection = secureClient.GetDatabase(db).GetCollection<BsonDocument>(coll);
// Insert a document into the collection
secureCollection.InsertOne(sampleDocFields);

When you insert a document, your CSFLE-enabled client encrypts the fields of your document such that it resembles the following:

{
  "_id": { "$oid": "<_id of your document>" },
  "name": "Jon Doe",
  "ssn": {
    "$binary": "<cipher-text>",
    "$type": "6"
  },
  "bloodType": {
    "$binary": "<cipher-text>",
    "$type": "6"
  },
  "medicalRecords": {
    "$binary": "<cipher-text>",
    "$type": "6"
  },
  "insurance": {
    "provider": "MaestCare",
    "policyNumber": {
      "$binary": "<cipher-text>",
      "$type": "6"
    }
  }
}

Tip

See: Complete Code

To view the complete code for inserting a document with encrypted fields, see our Github repository

5

Retrieve Your Document with Encrypted Fields

Retrieve the document with encrypted fields you inserted in the Insert a Document with Encrypted Fields step of this guide.

To show the functionality of CSFLE, the following code snippet queries for your document with a client configured for automatic CSFLE as well as a client that is not configured for automatic CSFLE.

Console.WriteLine("Finding a document with regular (non-encrypted) client.");
var filter = Builders<BsonDocument>.Filter.Eq("name", "Jon Doe");
var regularResult = regularCollection.Find(filter).Limit(1).ToList()[0];
Console.WriteLine($"\n{regularResult}\n");
Console.WriteLine("Finding a document with encrypted client, searching on an encrypted field");
var ssnFilter = Builders<BsonDocument>.Filter.Eq("ssn", 145014000);
var secureResult = secureCollection.Find(ssnFilter).Limit(1).First();
Console.WriteLine($"\n{secureResult}\n");

The output of the preceding code snippet should look like this:

Finding a document with regular (non-encrypted) client.
{
  _id: new ObjectId("629a452e0861b3130887103a"),
  name: 'Jon Doe',
  ssn: new Binary(Buffer.from("0217482732d8014cdd9ffdd6e2966e5e7910c20697e5f4fa95710aafc9153f0a3dc769c8a132a604b468732ff1f4d8349ded3244b59cbfb41444a210f28b21ea1b6c737508d9d30e8baa30c1d8070c4d5e26", "hex"), 6),
  bloodType: new Binary(Buffer.from("0217482732d8014cdd9ffdd6e2966e5e79022e238536dfd8caadb4d7751ac940e0f195addd7e5c67b61022d02faa90283ab69e02303c7e4001d1996128428bf037dea8bbf59fbb20c583cbcff2bf3e2519b4", "hex"), 6),
  'key-id': 'demo-data-key',
  medicalRecords: new Binary(Buffer.from("0217482732d8014cdd9ffdd6e2966e5e790405163a3207cff175455106f57eef14e5610c49a99bcbd14a7db9c5284e45e3ee30c149354015f941440bf54725d6492fb3b8704bc7c411cff6c868e4e13c58233c3d5ed9593eca4e4d027d76d3705b6d1f3b3c9e2ceee195fd944b553eb27eee69e5e67c338f146f8445995664980bf0", "hex"), 6),
  insurance: {
    policyNumber: new Binary(Buffer.from("0217482732d8014cdd9ffdd6e2966e5e79108decd85c05be3fec099e015f9d26d9234605dc959cc1a19b63072f7ffda99db38c7b487de0572a03b2139ac3ee163bcc40c8508f366ce92a5dd36e38b3c742f7", "hex"), 6),
    provider: 'MaestCare'
  }
}
Finding a document with encrypted client, searching on an encrypted field
{
  _id: new ObjectId("629a452e0861b3130887103a"),
  name: 'Jon Doe',
  ssn: 241014209,
  bloodType: 'AB+',
  'key-id': 'demo-data-key',
  medicalRecords: [ { weight: 180, bloodPressure: '120/80' } ],
  insurance: { policyNumber: 123142, provider: 'MaestCare' }
}

Tip

See: Complete Code

To view the complete code for finding a document with encrypted fields, see our Github repository

Learn More

To learn how CSFLE works, see CSFLE Fundamentals.

To learn more about the topics mentioned in this guide, see the following links:

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