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Encrypt a Realm - Flutter SDK

On this page

  • Overview
  • Considerations
  • Storing & Reusing Keys
  • Performance Impact
  • Encryption and Atlas Device Sync
  • Accessing an Encrypted Realm from Multiple Processes
  • Example

You can encrypt your realms to ensure that the data stored to disk can't be read outside of your application. You encrypt the realm on disk with AES-256 + SHA-2 by supplying a 64-byte encryption key when opening a realm.

Realm transparently encrypts and decrypts data with standard AES-256 encryption using the first 256 bits of the given 512-bit encryption key. Realm uses the other 256 bits of the 512-bit encryption key to validate integrity using a hash-based message authentication code (HMAC).


Do not use cryptographically-weak hashes for realm encryption keys. For optimal security, we recommend generating random rather than derived encryption keys.


Encrypt a Realm on Open or Copy Unencrypted Realm

You must encrypt a realm the first time you open it. If you try to open an existing unencrypted realm using a configuration that contains an encryption key, Realm throws an error.

Alternatively, you can copy the unencrypted realm data to a new encrypted realm using the Realm.writeCopy() method. Refer to Copy Data into a New Realm for more information.

The following are key impacts to consider when encrypting a realm.

You must pass the same encryption key in the realm's Configuration.encryptionKey property every time you open the realm. The key must be a 64-byte List<int>. To create a key that meets this specification, the List must contain exactly 64 integers and all integers must be between 0 and 255.

If you don't provide a key or specify the wrong key for an encrypted realm, the Realm SDK throws an error.

Apps should store the encryption key securely, typically in the target platform's secure key/value storage, so that other apps cannot read the key.

Reads and writes on encrypted realms can be up to 10% slower than unencrypted realms.

You can encrypt a synced realm.

Realm only encrypts the data on the device and stores the data unencrypted in your Atlas data source. Any users with authorized access to the Atlas data source can read the data, but the following still applies:

  • Users must have the correct read permissions to read the synced data.

  • Data stored in Atlas is always encrypted at a volume (disk) level.

  • The transfer between client and server is always fully encrypted.

You can also enable Customer Key Management to encrypt stored Atlas data using your cloud provider's key (e.g. AWS KMS, Azure Key Vault, Google Cloud KMS).

If you need unique keys for each user of your application, you can use an OAuth provider or use one of the Realm authentication providers and an authentication trigger to create a 64-bit key and store that key in a user object.

Changed in version 1.1.0.

Starting with Realm Flutter SDK version 1.1.0, Realm supports opening the same encrypted realm in multiple processes.

If your app uses Realm Flutter SDK version 1.1.0 or earlier, attempting to open an encrypted realm from multiple processes throws this error: Encrypted interprocess sharing is currently unsupported.

The following code demonstrates how to generate an encryption key and open an encrypted realm:

// Generate encryption key
final key = List<int>.generate(64, (i) => Random().nextInt(256));
final encryptedConfig = Configuration.local([Car.schema],
// Include the encryption key in the configuration
encryptionKey: key);
final encryptedRealm = Realm(encryptedConfig);
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