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Encrypt a Realm

You can 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).

You must pass the same encryption key when opening the realm again. Apps should store the encryption key in the Keychain so that other apps cannot read the key.

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

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:

// Generate a random encryption key
var key = Data(count: 64)
_ = key.withUnsafeMutableBytes { (pointer: UnsafeMutableRawBufferPointer) in
SecRandomCopyBytes(kSecRandomDefault, 64, pointer.baseAddress!) }
// Configure for an encrypted realm
var config = Realm.Configuration(encryptionKey: key)
do {
// Open the encrypted realm
let realm = try Realm(configuration: config)
// ... use the realm as normal ...
} catch let error as NSError {
// If the encryption key is wrong, `error` will say that it's an invalid database
fatalError("Error opening realm: \(error.localizedDescription)")
}

The following Swift example demonstrates how to store and retrieve a generated key from the Keychain:

// Retrieve the existing encryption key for the app if it exists or create a new one
func getKey() -> Data {
// Identifier for our keychain entry - should be unique for your application
let keychainIdentifier = "io.Realm.EncryptionExampleKey"
let keychainIdentifierData = keychainIdentifier.data(using: String.Encoding.utf8, allowLossyConversion: false)!
// First check in the keychain for an existing key
var query: [NSString: AnyObject] = [
kSecClass: kSecClassKey,
kSecAttrApplicationTag: keychainIdentifierData as AnyObject,
kSecAttrKeySizeInBits: 512 as AnyObject,
kSecReturnData: true as AnyObject
]
// To avoid Swift optimization bug, should use withUnsafeMutablePointer() function to retrieve the keychain item
// See also: http://stackoverflow.com/questions/24145838/querying-ios-keychain-using-swift/27721328#27721328
var dataTypeRef: AnyObject?
var status = withUnsafeMutablePointer(to: &dataTypeRef) { SecItemCopyMatching(query as CFDictionary, UnsafeMutablePointer($0)) }
if status == errSecSuccess {
// swiftlint:disable:next force_cast
return dataTypeRef as! Data
}
// No pre-existing key from this application, so generate a new one
// Generate a random encryption key
var key = Data(count: 64)
key.withUnsafeMutableBytes({ (pointer: UnsafeMutableRawBufferPointer) in
let result = SecRandomCopyBytes(kSecRandomDefault, 64, pointer.baseAddress!)
assert(result == 0, "Failed to get random bytes")
})
// Store the key in the keychain
query = [
kSecClass: kSecClassKey,
kSecAttrApplicationTag: keychainIdentifierData as AnyObject,
kSecAttrKeySizeInBits: 512 as AnyObject,
kSecValueData: key as AnyObject
]
status = SecItemAdd(query as CFDictionary, nil)
assert(status == errSecSuccess, "Failed to insert the new key in the keychain")
return key
}
// ...
// Use the getKey() function to get the stored encryption key or create a new one
var config = Realm.Configuration(encryptionKey: getKey())
do {
// Open the realm with the configuration
let realm = try Realm(configuration: config)
// Use the realm as normal
} catch let error as NSError {
// If the encryption key is wrong, `error` will say that it's an invalid database
fatalError("Error opening realm: \(error)")
}
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