# SecTransformRegister(_:_:_:) Registers a custom transform. ``` func SecTransformRegister(_ uniqueName: CFString, _ createTransformFunction: SecTransformCreateFP, _ error: UnsafeMutablePointer?>?) -> Bool ``` ## Parameters `uniqueName` A unique name for this custom transform. It is recommended that a reverse DNS name be used for the name of your custom transform `createTransformFunction` A [`SecTransformCreateFP`](/documentation/Security/SecTransformCreateFP) function pointer. The function must return a [`SecTransformInstanceBlock`](/documentation/Security/SecTransformInstanceBlock) block. Call block_copy on this block before returning it. Failure to do so results in undefined behavior. `error` A pointer that the function uses to provide an error object with details if an error occurs. The caller becomes responsible for the object’s memory. Pass `NULL` to ignore the error. ## Return Value A Boolean that is set to if the custom transform was registered and otherwise --- 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)