To clarify: this doesn't show what's supported and what's not, that's for you to find out by clicking things. It shows things in green that are generally consid

To clarify: this doesn't show what's supported and what's not, that's for you to find out by clicking things. It shows things in green that are generally considered secure. For example, 2048-bit finite-field ephemeral Diffie-Hellman (that's dh2048.badssl.com) is generally still considered secure, but Chrome doesn't allow it, so that's why you get that error even though the website shows it as green. Chrome does so for tangentially related, mostly-fine reasons. Generally dh2048 doesn't really exist on much of the Internet: because clients that don't do ECHDE (only DHE) are also generally limited to 1024-bit FFDH. That's not as good (not totally busted, but not great either). Anything that does 2048 bit FFDH probably also does ECDHE, and ECDHE is much better from a performance perspective and marginally better from a security perspective. The best classical attacks put P-256 at about 128 bits of security, and 2048 bit FF at about 112. Neither is problematic at present. FFDH has some other problems: because the other peer communicates the field over which you're going to work, a poorly configured or malicious peer could pick a bad field or a small subgroup. (That's a little esoteric, but since there's no good reason to keep it around anyway....)