Turktrust, the Turkish CA (certificate authority) responsible for issuing an intermediate CA certificate that was later used to generate an unauthorized certificate for google.com, claims that the bad Google certificate was not used for dishonest purposes.
On Thursday, Google, Mozilla, and Microsoft announced that they are blacklisting two intermediate CA certificates that were mistakenly issued by Turktrust in August 2011 for two of its customers who should have received normal end-entity certificates for their respective domain names.
An intermediate or subordinate CA (sub-CA) certificate inherits the trust given by browsers to the issuing CA and allows its owner to sign and create trusted SSL certificates for virtually any domain name on the Internet.
Turktrust's error was discovered after one of the mis-issued sub-CA certificates was used to sign a wildcard certificate for *.google.com without authorization from Google, the domain name owner. The rogue certificate was used on Dec. 24, 2012, in an attempt to inspect the encrypted communications of a Google Chrome user using a man-in-the-middle technique that consisted of re-encrypting the user's traffic en-route using the fraudulent certificate.
Because the Google Chrome browser contains a hardcoded list of legitimate Google certificates -- a feature called certificate pinning -- it is able to detect the use of unauthorized certificates and report the incidents back to Google.
In a statement published on its website, Turktrust explained that the mis-issuing of the two intermediate CA certificates was the result of an undetected certificate profile migration error between the company's testing and production systems. As a result, the production system used for certificate issuing ended up with two certificate profiles that contained CA extensions and were intended to be used only for testing purposes.
"The wrong profiles were only used on August 8, 2011 to issue those two faulty certificates which were certainly not intended to be sub-CA certificates," the company said.
The presence of the bad certificate profiles on the production system was detected a couple of days later and the error was corrected. However, the company failed to notice that two certificates with sub-CA status had been issued in the meantime.
According to Turktrust, the production system went through a successful audit by professional services company KPMG in November 2011 and was found compliant with the policy requirements for certification authorities that issue public key certificates, ETSI technical specification 102 042.
The company also claims to have implemented two additional verification procedures to prevent similar situations from happening in the future, one for checking various certificate characteristics during the certificate issuing process and one for checking already issued certificates before they are sent to customers.
One of the mis-issued sub-CA certificates had been revoked at the customer's request before being used, Turktrust said. The other was used on a Microsoft IIS (Internet Information Services) server that operated as a Web mail server for over a year, it said.