Change:
4.1. <del> As discussed in use-cases, there are use cases where it is desirable for multiple clients or multiple servers to share a PSK.  If this is done naively by having all members share a common key, then TLS authenticates only group membership, and the security of the overall system is inherently rather brittle.  There are a number of obvious weaknesses here: </del> <ins> As discussed in use-cases, to demonstrate their attack, AASS19 describes scenarios where multiple clients or multiple servers share a PSK.  If this is done naively by having all members share a common key, then TLS authenticates only group membership, and the security of the overall system is inherently rather brittle.  There are a number of obvious weaknesses here: </ins> Any group member can impersonate any other group member. <del> If PSK is combined with DH, then compromise of a group member that knows the resulting DH shared secret will enable the attacker to passively read (and actively modify) traffic. </del> <ins> If PSK is combined with a fresh ephemeral key exchange, then compromise of a group member that knows the resulting shared secret will enable the attacker to passively read (and actively modify) traffic. </ins> <del> If PSK is not combined with DH, then compromise of any group member allows the attacker to passively read (and actively modify) all traffic. </del> <ins> If PSK is not combined with fresh ephemeral key exchange, then compromise of any group member allows the attacker to passively read (and actively modify) all traffic. </ins> Additionally, a malicious non-member can reroute handshakes between honest group members to connect them in unintended ways, as described

Discussion:
NIT: Might be better to say: Just drops some redundant words.
I think some things that should be more positive: -- For both PSK authentication and PSK key exchange without (EC)DHE the bad security properties such as lack of identity protection and lack of forward secrecy can be overcome by using one-time PSKs. External PSKs with short lifetimes are quite common in many real deployments. I think this should be mentioned. -- I think quantum resistance should be mentioned earlier in the document. Quantum resistance is a security property, not use a use case. Some things that should be more negative: -- In the list in 4.1 you can add "4. Any group member can blame any other group member." Other comments: -- "then PSK-only key establishment modes are secure against both active and passive attack." I think this you need to describe the exact attacks you have in mind rather than use the work "secure". My view would be that acceptable security in 2021 includes both identity protection and forward secrecy. But more on a system level, then necessarily by TLS itself. -- "DH" I think it would be good to change all “DH” to “DHE” and all “Diffie-Hellman” to “ephemeral Diffie-Hellman” to avoid confusion with the static DH cipher suites in obsolete versions of TLS. -- "As discussed in Section 6, there are use cases where it is desirable for multiple clients or multiple servers to share a PSK." "However, as discussed in Section 6, there are application scenarios that may rely on sharing the same PSK among multiple nodes." Unless you have any real deployments to share, I think this should be reformulated. These are Gedankenexperiments used to illustrate the attack, not real-world applications. I would reformulate and remove "desirable", group PSKs should be very much discouraged. Suggestion: "As discussed in Section 6, to illustrate their attack, [Akhmetzyanova] describes scenarios where multiple clients or multiple servers share a PSK."