# SecKeyCopyExternalRepresentation(_:_:) Returns an external representation of the given key suitable for the key’s type. ``` func SecKeyCopyExternalRepresentation(_ key: SecKey, _ error: UnsafeMutablePointer?>?) -> CFData? ``` ## Parameters `key` The key to export. `error` The address of a object. If an error occurs, this is set to point at an error instance that describes the failure. ## Return Value A data object representing the key in a format suitable for the key type or `NULL` on error. In Objective-C, call the function to free the key’s memory when you are done with it. ## Discussion The operation fails if the key is not exportable, for example if it is bound to a smart card or to the Secure Enclave. It also fails in macOS if the key has the attribute [`kSecKeyExtractable`](/documentation/Security/kSecKeyExtractable) set to . The method returns data in the PKCS #1 format for an RSA key. For an elliptic curve public key, the format follows the ANSI X9.63 standard using a byte string of `04 || X || Y.` For an elliptic curve private key, the output is formatted as the public key concatenated with the big endian encoding of the secret scalar, or `04 || X || Y || K`. All of these representations use constant size integers, including leading zeros as needed. --- 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)