Accessing the system serial number programmatically

Developers of these applications often ask how to retrieve the system serial number that appears in the About This Mac window or in System Profiler. Prior to Mac OS X 10.3 "Panther", the only supported means of retrieving the serial number is to use AppleScript or Apple events to request this information from the System Profiler utility. However, starting with Panther, the serial number is presented in the property IOPlatformSerialNumber of the IOPlatformExpertDevice node in the I/O Registry. The I/O Registry accessor APIs in IOKit.framework can be used to retrieve this property from an application.

Listing 1  Reading the IOPlatformSerialNumber property

#include <CoreFoundation/CoreFoundation.h>
#include <IOKit/IOKitLib.h>

// Returns the serial number as a CFString. 
// It is the caller's responsibility to release the returned CFString when done with it.
void CopySerialNumber(CFStringRef *serialNumber)
{
    if (serialNumber != NULL) {
        *serialNumber = NULL;

        io_service_t    platformExpert = IOServiceGetMatchingService(kIOMasterPortDefault,
                                                                         IOServiceMatching("IOPlatformExpertDevice"));

        if (platformExpert) {
            CFTypeRef serialNumberAsCFString = 
                IORegistryEntryCreateCFProperty(platformExpert,
                                                CFSTR(kIOPlatformSerialNumberKey),
                                                kCFAllocatorDefault, 0);
            if (serialNumberAsCFString) {
                *serialNumber = serialNumberAsCFString;
            }

            IOObjectRelease(platformExpert);
        }
    }
}

Caveats for using the serial number

It is possible for a system to lose its serial number so that it will no longer appear either in System Profiler or the I/O Registry. Repairing a system by swapping hardware components is one reason this can happen. Apple does not document the specific details of how a machine can lose its serial number. Once the serial number has been lost there is no means to restore it to the machine.

Apple does not guarantee that all future systems will have a software-readable serial number.

Both of these cases illustrate why asset tracking software should always provide a way for a serial number to be entered manually.

Accessing the built-in MAC address programmatically

The primary MAC address can be read from the I/O Registry as shown in the sample Sample Code 'GetPrimaryMACAddress'.

Caveats for using the primary MAC address

The primary MAC address is associated with a particular system main logic board. So while the address is stable, it will change should the system's main logic board need to be replaced. Or, a customer may simply want to transfer their licensed content to a newly-purchased computer. DRM solutions relying on the primary MAC address should provide a means for users to re-register their licensed content to a different MAC address.

Netbooting introduces a wrinkle with systems with multiple built-in Ethernet ports. The primary Ethernet port on these systems is the one that is connected to the NetBoot server. This means that a search for the primary port may return either of the built-in MAC addresses depending on which port was used for netbooting. Note that "built-in" does not include Ethernet ports that reside on an expansion card.

There are other means for reading a MAC address programmatically besides the I/O Registry technique employed by the GetPrimaryMACAddress sample. One is to use the function getifaddrs. Another is to use the CFUUID APIs in Core Foundation. Versions of Mac OS X prior to Mac OS X 10.4 "Tiger" generated version 1 UUIDs, which contain a MAC address. (Tiger generates version 4 UUIDs which are generated from random numbers. See the Core Foundation release notes and RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace for details.)

Neither the getifaddrs nor the CFUUID methods are suitable for DRM purposes, especially on Mac OS X 10.3 or later. On Panther, the ifconfig utility supports the lladdr option to set a locally-administered MAC address for an interface. Both getifaddrs and the CFUUID APIs will return the locally-administered MAC address if one exists. A DRM product that relied on these APIs would be vulnerable to an admin user using ifconfig to specify the same MAC address on multiple machines.

Finally, it is possible for the built-in MAC address (or any I/O Registry property for that matter) to be spoofed by knowledgeable persons. If a more robust level of security is required, such as in cases where the licensed assets have a high monetary value, developers may want to investigate the numerous hardware security tokens that are available.

Caveats for using network registration

When using Bonjour in this way, pass in zero for the port number when registering your service. This will prevent these services from showing up when browsing.

Be sure to register a hash of the serial number, not the actual serial number, since it would be easy to use a packet sniffer to capture the raw serial number.

If the user has admin privileges, they can always disable the Bonjour daemon mDNSResponder. Be sure to test your application to make sure it behaves correctly in this situation.