Encryption (CSFLE)

Client Side Encryption is a feature that encrypts data in your application before it is sent to MongoDB. We recommend you get familiar with the concepts, ideally from the MongoDB Documentation to learn more about its capabilities and restrictions before you continue applying Encryption through Spring Data.

Make sure to set the drivers com.mongodb.AutoEncryptionSettings to use client-side encryption. MongoDB does not support encryption for all field types. Specific data types require deterministic encryption to preserve equality comparison functionality.

Automatic Encryption

MongoDB supports Client-Side Field Level Encryption out of the box using the MongoDB driver with its Automatic Encryption feature. Automatic Encryption requires a JSON Schema that allows to perform encrypted read and write operations without the need to provide an explicit en-/decryption step.

Please refer to the JSON Schema section for more information on defining a JSON Schema that holds encryption information.

To make use of a the MongoJsonSchema it needs to be combined with AutoEncryptionSettings which can be done eg. via a MongoClientSettingsBuilderCustomizer.

@Bean
MongoClientSettingsBuilderCustomizer customizer(MappingContext mappingContext) {
    return (builder) -> {

        // ... keyVaultCollection, kmsProvider, ...

        MongoJsonSchemaCreator schemaCreator = MongoJsonSchemaCreator.create(mappingContext);
        MongoJsonSchema patientSchema = schemaCreator
            .filter(MongoJsonSchemaCreator.encryptedOnly())
            .createSchemaFor(Patient.class);

        AutoEncryptionSettings autoEncryptionSettings = AutoEncryptionSettings.builder()
            .keyVaultNamespace(keyVaultCollection)
            .kmsProviders(kmsProviders)
            .extraOptions(extraOpts)
            .schemaMap(Collections.singletonMap("db.patient", patientSchema.schemaDocument().toBsonDocument()))
            .build();

        builder.autoEncryptionSettings(autoEncryptionSettings);
    };
}

Explicit Encryption

Explicit encryption uses the MongoDB driver’s encryption library (org.mongodb:mongodb-crypt) to perform encryption and decryption tasks. The @ExplicitEncrypted annotation is a combination of the @Encrypted annotation used for JSON Schema creation and a Property Converter. In other words, @ExplicitEncrypted uses existing building blocks to combine them for simplified explicit encryption support.

Fields annotated with @ExplicitEncrypted are always encrypted as whole. Consider the following example:

@ExplicitEncrypted(…)
String simpleValue;        (1)

@ExplicitEncrypted(…)
Address address;           (2)

@ExplicitEncrypted(…)
List<...> list;            (3)

@ExplicitEncrypted(…)
Map<..., ...> mapOfString; (4)

1	Encrypts the value of the simple type such as a `String` if not `null`.
2	Encrypts the entire `Address` object and all its nested fields as `Document`. To only encrypt parts of the `Address`, like `Address#street` the `street` field within `Address` needs to be annotated with `@ExplicitEncrypted`.
3	`Collection`-like fields are encrypted as single value and not per entry.
4	`Map`-like fields are encrypted as single value and not as a key/value entry.

Client-Side Field Level Encryption allows you to choose between a deterministic and a randomized algorithm. Depending on the chosen algorithm, different operations may be supported. To pick a certain algorithm use @ExplicitEncrypted(algorithm), see EncryptionAlgorithms for algorithm constants. Please read the Encryption Types manual for more information on algorithms and their usage.

To perform the actual encryption we require a Data Encryption Key (DEK). Please refer to the MongoDB Documentation for more information on how to set up key management and create a Data Encryption Key. The DEK can be referenced directly via its id or a defined alternative name. The @EncryptedField annotation only allows referencing a DEK via an alternative name. It is possible to provide an EncryptionKeyResolver, which will be discussed later, to any DEK.

Example 1. Reference the Data Encryption Key

@EncryptedField(algorithm=…, altKeyName = "secret-key") (1)
String ssn;

@EncryptedField(algorithm=…, altKeyName = "/name")      (2)
String ssn;

1	Use the DEK stored with the alternative name `secret-key`.
2	Uses a field reference that will read the actual field value and use that for key lookup. Always requires the full document to be present for save operations. Fields cannot be used in queries/aggregations.

By default, the @ExplicitEncrypted(value=…) attribute references a MongoEncryptionConverter. It is possible to change the default implementation and exchange it with any PropertyValueConverter implementation by providing the according type reference. To learn more about custom PropertyValueConverters and the required configuration, please refer to the Property Converters - Mapping specific fields section.

MongoEncryptionConverter Setup

The converter setup for MongoEncryptionConverter requires a few steps as several components are involved. The bean setup consists of the following:

The ClientEncryption engine
A MongoEncryptionConverter instance configured with ClientEncryption and a EncryptionKeyResolver.
A PropertyValueConverterFactory that uses the registered MongoEncryptionConverter bean.

A side effect of using annotated key resolution is that the @ExplicitEncrypted annotation does not need to specify an alt key name. The EncryptionKeyResolver uses an EncryptionContext providing access to the property allowing for dynamic DEK resolution.

Example 2. Sample MongoEncryptionConverter Configuration

class Config extends AbstractMongoClientConfiguration {

    @Autowired ApplicationContext appContext;

    @Bean
    ClientEncryption clientEncryption() {                                                            (1)
        ClientEncryptionSettings encryptionSettings = ClientEncryptionSettings.builder();
        // …

        return ClientEncryptions.create(encryptionSettings);
    }

    @Bean
    MongoEncryptionConverter encryptingConverter(ClientEncryption clientEncryption) {

        Encryption<BsonValue, BsonBinary> encryption = MongoClientEncryption.just(clientEncryption);
        EncryptionKeyResolver keyResolver = EncryptionKeyResolver.annotated((ctx) -> …);             (2)

        return new MongoEncryptionConverter(encryption, keyResolver);                                (3)
    }

    @Override
    protected void configureConverters(MongoConverterConfigurationAdapter adapter) {

        adapter
            .registerPropertyValueConverterFactory(PropertyValueConverterFactory.beanFactoryAware(appContext)); (4)
    }
}

1	Set up a `Encryption` engine using `com.mongodb.client.vault.ClientEncryption`. The instance is stateful and must be closed after usage. Spring takes care of this because `ClientEncryption` is `Closeable`.
2	Set up an annotation-based `EncryptionKeyResolver` to determine the `EncryptionKey` from annotations.
3	Create the `MongoEncryptionConverter`.
4	Enable for a `PropertyValueConverter` lookup from the `BeanFactory`.