Boulder: Allow secp521r1 for dual-certificate (ECDSA+RSA) postfix setup

[Darkspirit]

I would love to use the same security level as symmetric 265 bit (Level: 8 https://www.keylength.com/en/3/ ) with asymmetric crypto for mail delivery. Nearly everyone uses OpenSSL. Old Windows servers can still connect via RSA. I don't want to be forced to use self-signed certs any longer. https://ssl-tools.net/mailservers/terrax.net Because acme.sh supports "ec-521", it would be enough to enable it on the server side (and not in the LE client for normal users).

[rolandshoemaker]

Closing as duplicate of #1592/won't fix for now. Browser support hasn't changed, Chrome dropped support and NSS is considering dropping it. Browser based SSL/TLS is our main focus so the extra complexity just isn't worth it yet.

It should also be noted that a number of dependencies that we rely on, such as SoftHSM, don't support secp521r1 which would prevent us from doing any local testing for that curve.

[Darkspirit]

It's worth fighting for keeping long-term security encryption (P-521) in NSS! :-)
Only because Google wants to clean their code for their needs, other users shouldn't be forced to optimize everything for Chrome. ^^ We want to use long-term encryption for the browsers (only firefox) and mail clients (thunderbird) of the members of our non-profit organization.

Please consider this: https://github.com/letsencrypt/boulder/pull/1298#issuecomment-167356451
"Disabled P521 for now. You can uncomment it safely if you wish."

[Darkspirit]

A long time ago, there was somebody who implemented an algorithm whitelist in boulder:

Disabled P521 for now. You can uncomment it safely if you wish. https://github.com/letsencrypt/boulder/pull/1298#issuecomment-167356451

Reopening the original Issue https://github.com/letsencrypt/boulder/issues/2143 with this.

@rolandshoemaker
won't fix for now. https://github.com/letsencrypt/boulder/issues/2143#issuecomment-243872905

• Browser support hasn't changed

-> Solved. Mozilla wants to keep P-521, to implement new curves and to force Google to follow. Apple and Android always had P-521. You can use it on Windows Servers and you can activate it in Windows Clients (mostly already done in business enviroments).

• NSS is considering dropping it

-> Solved. Closed as wontfix. They don't want to weaken security.

• dependencies that we rely on, such as SoftHSM, don't support secp521r1 which would prevent us

-> Solved. SoftHSM implemented P-521 25 days ago

So it would be fine to enable P-521 for manual requests over acme to not confuse normal users of the letsencrypt client.