Earlier quoted context omitted.
This is exactly the conclusion I came to. My guess is they have the SSL/TLS keys. That being said, tptacek thinks we are wrong, and he is a subject matter expert, so I am not sure.
The linked quora answer (from the co-author of Firesheep) says that even in that case one can't launch a passive man in the middle attack if perfect forward secrecy is used. Google.com uses Diffie–Hellman key exchange which provides perfect forward secrecy. So... If I understand everything correctly, it should be impossible to decrypt passively captured HTTPS traffic to/from google.com. http://www.quora.com/SSL-Secur…
Ian Gallager: > so if you have the private key, you can decrypt that key, and then use it to decrypt the bulk-encrypted data.
Like he says, if you have the key, wireshark can decrypt the data trivially.
If you have the CA master keys, then the only thing you can do is perform a MITM attack, but not silently decrypt the raw data. A MITM attack would eventually get detected.