Re: [radext] WGLC #2 for draft-ietf-radext-dtls-04

[Peter Deacon <[e-mail]>]

On Mon, 8 Apr 2013, Alan DeKok wrote:

> Sam Hartman wrote:
>> Can you point to the documentation of the hard requirement for
>> server-side memory in upgrade?
>> I'd like to understand how we got there and the discussions/arguments
>> leading to that.

>  Down-bidding attacks.

A bidding down attack requires client or server to be tricked into 
accepting security lower than highest supported by both peers.  See the 
table in my previous message.

>  Once a client upgrades to DTLS, allowing plain UDP is a down-bidding
> attack.

To be an attack the attack must be successful. With RADIUS/DTLS draft 
there is no negotiation protocol to attack.  Either the nonnegotiable 
demands of both sides are met or it fails.

A client configured to only emit RADIUS/DTLS requests cannot be tricked 
into falling back to a less secure RADIUS/UDP.


Likewise a server willing to accept RADIUS/UDP and RADIUS/DTLS cannot be 
tricked into accepting RADIUS/UDP as RADIUS/UDP has been configured to be 
acceptable to the server.

A server willing to accept only RADIUS/DTLS cannot be tricked into 
accepting RADIUS/UDP.  This is a setting on the server rather than 
negotiation parameter able to be attacked from the protocol.

regards,
Peter