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PSK based resumption vs session ID/ticket based resumption in TLS

cn flag

I was reading about TLS 1.3, and noticed how session resumption was done via PSKs instead of Session IDs/Session Tickets. But from what I've understood, PSKs just seem like a combination of Session IDs and Session Tickets mechanism (the psk identity acting as session IDs and the New Session Ticket acting as the session ticket).

My question is, why has the PSK method been employed over the previous two methods in TLS 1.3? Are there any advantages of having chosen this? When reading about Session Tickets, I thought it was pretty neat, apart from the single point of failure existing due to the secret key used for decrypting the session ticket. But the PSK method also need psk identity which needs to be stored in the server cache. Isn't that disadvantageous, as the server has to store the IDs? So why are PSKs used at all?

Related to the Session Ticket mechanism, I also wanted to know if the servers store a separate private keys (for encrypting the session tickets) for separate clients? Is that how session tickets are disadvantageous because the server has to maintain separate keys for separate client sessions?

dave_thompson_085 avatar
cn flag
Although the fields in 1.3 are named/described as 'identity', it only needs to be unique and can be up to 64KB. A ticket in the 4507/5077 sense is by construction unique and should fit in 64KB, so it can _be_ an 'identity' that requires no actual storage on server. Effectively dupe https://crypto.stackexchange.com/questions/53806/does-tls-1-3-really-send-psks-encrypted . Since one PSK mechanism (as modified for 1.3) supports all three usages, why make the protocol more complicated and implementation harder?
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