All ANT products ship as standard with the public network key, by default assigned to network number 0.
You can also find the public network key here.
Please note that the public network key is not 00-00-00-00-00-00-00-00, which is actually an invalid key. Entering an invalid network key results in the last valid network key being used (which usually is the default public network key). See this FAQ for more details.