I use CURL in PHP to connect with https://secure.authorize.net/gateway/transact.dll . Recently, few days ago, I got the CURL error message : SSL certificate problem: unable to get local issuer certificate . This problem might have started after an update of my CA bundle. My CA bundle is taken from http://curl.haxx.se/ca/cacert.pem , I checked the required chain and neither the required root certificate or any of the intermediary certificates in the chain were available in the most recent version of that list. I manually added the required root certificate in the file and the problem was solved. However, I would have expexted that the required root certificate used by Authorize.net would have been sufficiently trusted to have been already included in this very standard list. Any explanation? I also asked for explanation at Stack Overflow http://stackoverflow.com/questions/29103613/how-comes-authorize-net-uses-a-certificate-that-is-signe... , but no one seems to know the answer,
