Re: [Uta] I-D Action: draft-ietf-uta-rfc7525bis-03.txt

[Ilari Liusvaara <[e-mail]>]

On Mon, Oct 25, 2021 at 02:58:32PM +0300, Yaron Sheffer wrote:
> This is a relatively small rev from -02, with more clarity on key
> limits and mitigation of Triple Handshake (extended_master_secret). 
> 
> Our open issues are at https://github.com/yaronf/I-D/issues - fell
> free to comment or open new ones.
> 
> On 10/25/21, 14:53, "[e-mail] on behalf of [e-mail]" <[e-mail] on behalf of [e-mail]> wrote:
> 
> 
>     	Filename        : draft-ietf-uta-rfc7525bis-03.txt


"It is also RECOMMENDED that clients abort the handshake if the server
acknowledges the SNI hostname with a different hostname than the one
sent by the client."

AFAIK, this can not happen. From RFC 6066:

"In this event, the server SHALL include an extension of type
'server_name' in the (extended) server hello.  The 'extension_data'
field of this extension SHALL be empty."

So the server can not acknowledge name different from what the
client sent. Then there are some servers that do take client server_name
into account, but fail to acknowledge that.

Server certificate (if raw public keys are not used) is supposed to
be valid for the SNI hostname, but it can be valid for other names
as well. So it is not really acknowledgement for the SNI hostname.
However, it would make sense for clients to abort if server certificate
is not valid for sent SNI hostname.


-Ilari