# SecCertificateCopySerialNumberData(_:_:) Returns the certificate’s serial number. ``` func SecCertificateCopySerialNumberData(_ certificate: SecCertificate, _ error: UnsafeMutablePointer?>?) -> CFData? ``` ## Parameters `certificate` The certificate from which to copy the serial number. `error` A pointer the function uses to return an error instance on failure. Set to `nil` to ignore any error. ## Return Value The content of a DER-encoded integer (without the tag and length fields) for this certificate’s serial number. ## Discussion In Objective-C, if the function returns an error free it with a call to when you are done with it. If it returns data, you must free that as well. --- 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)