# SecSignTransformCreate(_:_:) Creates a signing transform object. ``` func SecSignTransformCreate(_ key: SecKey, _ error: UnsafeMutablePointer?>?) -> SecTransform? ``` ## Parameters `key` A [`SecKey`](/documentation/Security/SecKey) with the private key used for signing. `error` A pointer to a . This pointer will be set if an error occurred. This value may be `NULL` if you do not want an error returned. ## Return Value A pointer to a new transform or `NULL` on error. In Objective-C, call the function to free this object’s memory when you are done with it. ## Discussion This function creates a transform which computes a cryptographic signature. The [`kSecInputIsAttributeName`](/documentation/Security/kSecInputIsAttributeName) attribute defaults to [`kSecInputIsPlainText`](/documentation/Security/kSecInputIsPlainText), and the [`kSecDigestTypeAttribute`](/documentation/Security/kSecDigestTypeAttribute) and [`kSecDigestLengthAttribute`](/documentation/Security/kSecDigestLengthAttribute) attributes default to something appropriate for the type of key you have supplied. --- 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)