# init(_:) Creates a new custom context that provides a unique string. ``` init?(_ string: String) ``` ## Parameters `string` The string to use as the underlying context, which must be equal to or greater than three characters long. The framework converts the string to UTF-8 prior to hashing it in the derivation. ## Return Value A new `Context`, or `nil` if the provided string was too short ## Discussion The custom context may use any string that is representable as UTF-8, and which normalizes to the same value when represented as bytes. A best practice is to use ASCII-compatible values to avoid normalization issues. Set the same byte value on the local and remote devices in order to generate the same shared secret. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)