Re: [CFRG] How will Kyber be added to HPKE (9180)?

[Mike Ounsworth <[e-mail]>]

Hi Peter,

If the CMP client doesn't cheat (sign with an RSA encryption key), then how do you do message protection (integrity protection / authentication) when the client has an RSA encryption key? I don't see anything in there that would apply to a keyEncipherment mode?

5.1.3. PKI Message Protection .............................28
     5.1.3.1. Shared Secret Information .................29
     5.1.3.2. DH Key Pairs .......................................30
     5.1.3.3. Signature ............................................30
      5.1.3.4. Multiple Protection ...........................30


Maybe you could do an RSA key transport to establish a key and then use the PasswordBasedMac in 5.1.3.1? Are there implementations that do that? It's certainly not mentioned in the text that PasswordBasedMac is meant to be combined with RSA key transport.

---
Mike Ounsworth

-----Original Message-----
From: Peter Gutmann <[e-mail]>
Sent: November 25, 2022 10:56 PM
To: Mike Ounsworth <[e-mail]>; Kampanakis, Panos <[e-mail]>
Cc: [e-mail]
Subject: [EXTERNAL] Re: [CFRG] How will Kyber be added to HPKE (9180)?

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______________________________________________________________________
Mike Ounsworth <Mike.Ounsworth=[e-mail]> writes:

>I believe if you have an RSA key marked with keyUsage:keyEncipherment
>then you just cheat and sign with it anyway.

That'll only work if you've got a badly-written implementation
*cough*CryptoAPI*cough* that ignores key usages, for anything that does enforce them it won't work.  It's bad enough having to kludge around this issue for PKCS #10 without introducing the same problem into CMP.

Peter.

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