Encrypt a Realm


You can the encrypt the realm database file 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).


Storing & Reusing Keys

You must pass the same encryption key when opening the encrypted realm again. Apps should store the encryption key securely.

Performance Impact

Typically, reads and writes on encrypted realms can be up to 10% slower than unencrypted realms.

Encryption and Realm Sync

You can encrypt a synced realm. MongoDB Realm only encrypts the data on the device and stores the data unencrypted in your MongoDB Atlas data source.


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

// Retrieve key from secure location or create one...
const key = new Int8Array(64); // Populate with a secure key
// ... store key ...

// Use key to open realm{ schema: [DogSchema], encryptionKey: key }).then((realm) => {
  // Use the realm as normal
  const dogs = realm.objects("Dog");

  // ...