Function

SecKeyCopyExternalRepresentation(_:_:)

Returns an external representation of the given key suitable for the key's type.

Declaration

func SecKeyCopyExternalRepresentation(_ key: SecKey, _ error: UnsafeMutablePointer<Unmanaged<CFError>?>?) -> CFData?

Parameters

key

The key to export.

error

The address of a CFError 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 nil on error.

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 set to false.

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.

See Also

Import and Export

Storing Keys as Data

Create an external representation of a key for transmission.