[Cryptography] ALPACA

[Jerry Leichter]

> 
>> TLS certificates validate host names, not IP addresses or port
>> numbers.
> 
> Well, TLS certificates can validate arbitrary Subject Alternative Names,
> which can be more specific that just a hostname.  The real issue is that
> hostnames are the only things that the CA/B forum issuers (i.e.  Let's
> Encrypt) know how to issue DV certificates for....
The paper points out that the entire technique can be avoided if the web site uses SNI *and marks SNI as required*.  The problem is that (a) "SNI required" is almost never used in practice; (b) even if requested, many existing servers don't enforce it, even some that say they do.  Of course, these two facts are self-reinforcing.
                                                        -- Jerry