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Discuss PSK authentication method and resumption method (lightweight)
- Similar to what was done with PSK/resumption mechanism in TLS 1.3.
- External and internal PSK
The method should still provide ephemeral key exchange, identity protection and mitigate tracking and fingerprinting.
Benefits:
- 1 asymmetric operation compared to three in current methods.
- eliminates external things like fetching credentials from a database, revocation and path validation.

Key scheduling
- Add ID_PSK in message 1. Remove ID_CRED_R and ID_CRED_I in m2 and m3, respectively.
- Add PSK to salt to derive PRK_2e (salt = [TH_2, PSK]).
- PRK_3e2m, PRK_4e3m and PRK_2e should be different. (MAC orcale Jacomme)
- Derive resumption PSK = EDHOC_KDF(PRK_out, 11, h'', h_len

Discussion