Re: [radext] TLS-PSK and RADIUS/(D)TLS - MTI trust models

[Alan DeKok <[e-mail]>]

On Aug 13, 2023, at 1:38 PM, Margaret Cullen <[e-mail]> wrote:
>> That is a tried and true RADIUS tradition.  "I know the RFCs say to do X, but I'll just do something else instead."
> 
> That tradition extends well beyond RADIUS, unfortunately.

   True.

> I think RADIUS/DTLS is an awful lot to expect, though — especially because I don’t see any evidence that RADIUS/DTLS will ever be widely implemented or used.  Do you?

  radsecproxy implements it.  I plan on implementing it soon in FreeRADIUS.

  Cisco supports it: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/16-3/configuration_guide/b_163_consolidated_3850_cg/b_163_consolidated_3850_cg_chapter_01100010.pdf

  There's not a lot of information on other implementations.

> Many protocols that run over TLS don’t have a DTLS equivalent defined, at all.  Is there some important advantage that RADIUS/DTLS offers that RADIUS/TLS does not?  Is that advantage sufficient to warrant mandating both in every server implementation?

  UDP is generally a much better transport for RADIUS than TCP.  So DTLS is likely to have fewer problems than TLS, for the same reasons.

>> There's good reason for that, of course.  But I think it's best to document the system we need, rather than the system we have.
> 
> I absolutely agree with this when it comes to documenting good protocol behavior, ways to avoid known issues, etc.  I don’t think it extends to mandating the implementation of an entirely separate protocol.
> 
>> The alternative is to never fix RADIUS, or to give bad implementations a free pass.
> 
> Is there a reason that you think a RADIUS/TLS-only server would be a bad implementation, and that it would  become a good implementation if it also implemented RADIUS/DTLS?

  Mainly due to UDP versus TCP issues.

 I can't recall a customer deployment where we did RADIUS over TCP.  The choices for secure networks (VPN, etc) are UDP.  RADIUS/TLS is used only as a security layer for packets being sent over the Internet.

  I think if DTLS was widely available, I would recommend that people prefer it to TLS pretty much all of the time.  The ALPN draft only makes this difference more pronounced in favour of UDP, I think.

  Alan DeKok.