---
title: "SecKeyCopyExternalRepresentation(_:_:)"
framework: security
role: symbol
role_heading: Function
path: "security/seckeycopyexternalrepresentation(_:_:)"
---

# SecKeyCopyExternalRepresentation(_:_:)

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

## Declaration

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

## Parameters

- `key`: The key to export.
- `error`: The address of a doc://com.apple.documentation/documentation/CoreFoundation/CFError object. If an error occurs, this is set to point at an error instance that describes the failure.

## Mentioned in

Storing Keys as Data

## Return Value

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 CFRelease function to free the key’s memory when you are done with it.

## Discussion

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.