By "mandating use of PPK" I meant in RFC8784 PPK is already a negotiated 
option, but in order to prevent attacker remove the USE_PPK notification, both 
sides need to have policy to mandate PPK must be used.
Of course, we can't assume all implementations support PPK, but it is same we 
can't assume all implementations will support new protocol changes this draft 
introduces specifically the changes in the draft is not trivial; at least 
RFC8784 has been out for a while, and I know quite some ipsec implementations 
already supported it.
I think if the WG adopt this draft, there should be texts in the draft 
mentioning all these mitigations beside protocol changes.

From: Christopher Patton <[email protected]>
Sent: Thursday, July 31, 2025 6:08 AM
To: Blumenthal, Uri - 0553 - MITLL <[email protected]>
Cc: Jun Hu (Nokia) <[email protected]>; Michael Richardson 
<[email protected]>; Valery Smyslov <[email protected]>; Scott Fluhrer 
<[email protected]>; ipsec <[email protected]>
Subject: Re: [EXT] [IPsec] Re: draft-smyslov-ipsecme-ikev2-downgrade-prevention


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Hi Uri and Jun,

I agree - mandating use of PPK may not work. However, suggesting use of PPK, 
i.e., as a (negotiable?) option would be a very good thing: those who have the 
ability to employ it, and want better security - would opt in. While those who 
don't care or for various reasons cannot manage the distribution - could opt 
out.

This sounds like a good idea to me! 
https://github.com/smyslov/ikev2-downgrade-prevention/issues/5

Chris P.
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