Recently, I have been looking at PKI and certificates, and TLS 1.2 as part of my study of cryptography. I have the understanding that the public key included in the certificate of a website is the key that is used to establish a session key between two parties.

But on certain websites, when I opened Google Chrome security overview by clicking on the green https padlock, Chrome informed me that the key exchange was done by ECDHE with P-256 (Elliptic Curve Diffie-Hellman, curve P-256). But, upon opening the full certificate details for the website, the public key in the certificate was an RSA 2048 bit public key. But, this confused me, as I thought it should be an ECDHE key and I am not sure whether the key exchange is done by ECDHE, as Chrome says, or RSA, which is the public key in the certificate, which I thought was used in the key establishment.

Any help would be appreciated.