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[AVTCORE] Re: STUN SHA-256 usage in WebRTC (ICE and TURN)

Philipp Hancke <philipp.hancke@googlemail.com> Wed, 29 April 2026 17:56 UTC

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From: Philipp Hancke <philipp.hancke@googlemail.com>
Date: Wed, 29 Apr 2026 19:55:07 +0200
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Subject: [AVTCORE] Re: STUN SHA-256 usage in WebRTC (ICE and TURN)
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After reading a bit more (with help):
- TURN is solved by the initial response having a password-algorithms
attribute.
- the RFC 8489 hash agility plan changed.
https://www.rfc-editor.org/rfc/rfc8489#section-16.3 says that
      STUN clients and servers using the short-term credential mechanism
      will need to update the external mechanism that they use to signal
      what message-integrity attributes are in use
which simply was never done for ICE?

Am Mi., 29. Apr. 2026 um 19:23 Uhr schrieb Philipp Hancke <
philipp.hancke@googlemail.com>:

> Am Mi., 29. Apr. 2026 um 18:32 Uhr schrieb Roman Shpount <
> roman@telurix.com>:
>
>> On Wed, Apr 29, 2026 at 12:20 PM Roman Shpount <roman@telurix.com> wrote:
>>
>>> It looks like the details of the MESSAGE-INTEGRITY-SHA256 implementation
>>> were fully considered. What is described in RFC 8489 is counterproductive.
>>> If MESSAGE-INTEGRITY-SHA256 is comprehension-required, including
>>> MESSAGE-INTEGRITY also makes STUN messages less secure. It should have been
>>> in the comprehension-optional range.
>>>
>>> You should also consider the increase in STUN message size. Adding
>>> optional MESSAGE-INTEGRITY-SHA256 will result in an extra 32 bytes in each
>>> STUN request.
>>>
>>
>> I meant to say the details of the MESSAGE-INTEGRITY-SHA256 implementation
>> were NOT fully considered.
>>
>
> Heh! I assume the RFC is not fixable as an error but requires an update?
>
> The downgrade attack argument is good (applies to most hash agility plans
> I have seen though?) but if we need an ice-option or url parameter anyway
> it goes away.
> This reduces the concern about increasing overhead on initial messages
> requests would have to include both variants (4+20 plus 4 + 32) so we are
> only increasing packet size by 12 bytes?
>
> Thanks Roman for helping me think!
>
>>

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