Field Level Encryption from the .NET SDK

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    A practical guide for getting started with Field-Level Encryption, showing how to encrypt and decrypt JSON fields using the .NET SDK.

    For a high-level overview of this feature, see the Field-Level Encryption discussion doc.

    Packaging

    The Couchbase .NET SDK works together with the .NET Couchbase Encryption library to provide support for encryption and decryption of JSON fields. This library includes cryptographic algorithms and keyrings you can use out of the box, and provides a framework for implementing your own crypto components.

    The encryption code is packaged as an optional library because it is released under a different license from the Couchbase .NET SDK. To use the encryption library, you have to explicitly include this dependency in your project configuration. Refer to the dependencies section.

    Requirements

    • Couchbase .NET SDK version 3.1.3 or later.

    • .NET Couchbase Encryption version 2.0.0-dp.1 or later.

    NuGet Package

    <PackageReference Include="Couchbase.Extensions.Encryption" Version="2.0.0-dp.1" />

    See the NuGet Package Page for the latest version.

    Configuration

    To enable Field-Level Encryption, create a CryptoManager and supply EncryptedFieldTranscoder as an Options on the K/V operation.

    var provider =
        new AeadAes256CbcHmacSha512Provider(
            new AeadAes256CbcHmacSha512Cipher(), new Keyring(new IKey[]
            {
                new Key("test-key", GetFakeKey(64))
            }));
    
    var cryptoManager = DefaultCryptoManager.Builder()
        .Decrypter(provider.Decrypter())
        .DefaultEncrypter(provider.Encrypter("test-key"))
        .Build();
    
    var encryptedTranscoder = new EncryptedFieldTranscoder(cryptoManager);
    
    var clusterOptions = new ClusterOptions()
        .WithTranscoder(encryptedTranscoder)
        .WithConnectionString("couchbase://localhost")
        .WithCredentials("Administrator", "password");
    
    var cluster = await Cluster.ConnectAsync(clusterOptions);
    var bucket = await cluster.BucketAsync("travel-sample");

    Usage

    Two modes of operation are available:

    • Transparent encryption/decryption using EncryptedFieldAttribute on POCOs on deserialization/serialization.

    • Manual field editing using JObjectExtensions and the CryptoManager itself.

    Data Binding Example

    Sensitive fields of your data classes can be annotated with EncryptedField. Let’s use this class as an example:

    public class Employee
    {
        [EncryptedField(KeyName = "test-key")]
        public bool IsReplicant { get; set; }
    }

    Now let’s create an employee record and save it to Couchbase:

    var collection = await bucket.DefaultCollectionAsync();
    
    await collection.UpsertAsync(id, employee, options => { options.Expiry(TimeSpan.FromSeconds(10)); })
        .ConfigureAwait(false); //encrypts the IsReplicant field

    You can get the document as a JsonObject to verify the field was encrypted:

    var getResult1 = await collection.GetAsync(id, options => options.Transcoder(encryptedTranscoder))
        .ConfigureAwait(false);
    
    var encrypted = getResult1.ContentAs<JObject>();
    Console.WriteLine(encrypted);

    Because contentAsObject() does not decrypt anything, the expected output is something like:

    {
      "encrypted$replicant": {
        "alg": "AEAD_AES_256_CBC_HMAC_SHA512",
        "ciphertext": "xwcxyUyZ.....",
        "kid": "myKey"
      }
    }

    Now let’s read the employee record using data binding:

    var getResult2 = await collection.GetAsync(id, options => options.Transcoder(encryptedTranscoder))
        .ConfigureAwait(false);
    
    var readItBack = getResult2.ContentAs<Employee>();
    Console.WriteLine(readItBack.IsReplicant);

    This prints true.

    Creating Encryption Keys

    The AEAD_AES_256_CBC_HMAC_SHA512 algorithm included in this library uses encryption keys that are 64 bytes long.

    Here’s an example that shows how to create a suitable encryption key:

    var keyBytes = new Span<byte>(new byte[64]);
    RandomNumberGenerator.Fill(keyBytes);
    
    var keyRing = new Keyring(new IKey[]
    {
        new Key("my-key", keyBytes.ToArray())
    });

    And here’s how to use it to create a Keyring for use with Couchbase Field-Level Encryption:

    var provider =
        new AeadAes256CbcHmacSha512Provider(
            new AeadAes256CbcHmacSha512Cipher(), new Keyring(new IKey[]
            {
                new Key("test-key", GetFakeKey(64))
            }));
    
    var cryptoManager = DefaultCryptoManager.Builder()
        .Decrypter(provider.Decrypter())
        .DefaultEncrypter(provider.Encrypter("test-key"))
        .Build();

    Migrating from SDK 2

    SDK 2 cannot read fields encrypted by SDK 3.

    It’s inadvisable to have both the old and new versions of your application active at the same time. The simplest way to migrate is to do an offline upgrade during a scheduled a maintenance window. For an online upgrade without downtime, consider a blue-green deployment.

    SDK 3 requires additional configuration to read fields encrypted by SDK 2. The rest of this section describes how to configure Field-Level Encryption in SDK 3 for backwards compatibility with SDK 2.

    Changing the field name prefix

    In SDK 2, the default prefix for encrypted field names was __crypt_. This caused problems for Couchbase Sync Gateway, which does not like field names to begin with an underscore. In SDK 3, the default prefix is encrypted$.

    For compatibility with SDK 2, you can configure the CryptoManager to use the old __crypt_ prefix:

    var cryptoManager = DefaultCryptoManager.Builder()
        .EncryptedFieldNamePrefix("__crypt_")
        //other config
        .Build();
    In SDK 2, only top-level fields could be encrypted. SDK 3 allows encrypting fields at any depth. If you decide to rename the existing fields, make sure to do so before writing any encrypted fields below the top level, otherwise it may be difficult to rename the nested fields using a generic N1QL statement.

    Enabling decrypters for legacy algorithms

    The encryption algorithms used by SDK 2 are deprecated, and are no longer used for encrypting new data. To enable decrypting fields written by SDK 2, register the legacy decrypters when configuring the CryptoManager:

    var cryptoManager = DefaultCryptoManager.Builder()
        .LegacyAesDecrypters(keyring, "hmacKey")
        .DefaultEncrypter(provider.Encrypter("upgrade-key"))
        .Decrypter(provider.Decrypter())
        .Build();
    The legacy decrypters require a mapping function. For AES, this function accepts an encryption key name and returns the corresponding signing key name. For RSA, this function accepts a public key name and returns the corresponding private key name.