Re: [TLS] Working Group Last Call for draft-ietf-tls-sslv3-diediedie-00

On Mon, Mar 2, 2015 at 3:24 PM, Martin Rex <mrex@sap.com> wrote:
> Erik Nygren wrote:
>> Is it worth adding in a note to section 4 (Limited Capabilities) of:
>>
>> * Server Name Indication to enable virtual hosting of multiple hosts with
>> independent certificates on a single IP address
>>
>> ?
>>
>> I'm not sure if it's critical enough to hold up last-call?  It is another
>> major down-side of the lack of extension support in SSLv3 from a
>> deploy-ability perspective.
>
>
> Your notion seems to be based on a urban legend.
>
> SSLv3 (the protocol), in the final, after-the-fact publication
> of November 18, 1996 (which the IETF failed to publish for 15 years,
> but finally did as https://tools.ietf.org/html/rfc6106 ),
> has _the_exact_same_ support for extensions as TLSv1.0.
>
> Implementations of SSLv3, however, do not necessarily make use of
> that capability.

Actually, the RFC you meant was RFC 6101
(https://tools.ietf.org/html/rfc6101). The word extension doesn't
appear in the draft, instead all we see is a forward compatibility
note, stating that extra data may appear after the hello.

It's true that RFC 2246 doesn't mandate extension support either. But
RFC 3546 defines extensions for TLS 1.0, not SSLv3.0. Of course, you
could say that SSL v3.0 extensions should be supported the same way as
TLS 1.0. But there's no indication that this is actually what the
documents mean, or how servers and clients are actually implemented.
>
> SNI has only limited value, and provides an additional attack surface, e.g.
>   https://bh.ht.vc/vhost_confusion.pdf

Multitenancy is incredibly common, especially given IPv4 exhaustion.
Absent SNI, there is no good way for CDNs to function.

Sincerely,
Watson Ladd

>
>
> Personally, I'm much more concerned about newer software that breaks
> horribly when no TLS extension SNI is present in the ClientHello,
> such as Microsoft ADFS 2012.
>
>
> -Martin
>
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