The question comes from the accepted answer in this thread: My understanding of how HTTPS works (gmail for example)
The Gmail server sends your client a certificate. The certificate includes the Gmail server's public key, and some evidence that this public key actually belongs to gmail.com.
Your browser verifies the evidence in the certificate, to confirm that it has the proper public key for gmail.com.
Your browser chooses a random new symmetric key K to use for its connection to Gmail. It encrypts K under Gmail's public key.
Gmail decrypts K using its private key. Now both your browser and the Gmail server know K, but no one else does.
Anytime your browser wants to send something to Gmail, it encrypts it under K; the Gmail server decrypts it upon receipt. Anytime the Gmail server wants to send something to your browser, it encrypts it under K.*
Regarding this step, "your browser chooses a random new symmetric key K", what is the number of bits in this key that the browser generates?
From another thread I posted (see: Understanding 2048 bit SSL and 256 bit encryption), I get the impression that it's a 256 bit key.
How can I verify this?