[CFRG] [Technical Errata Reported] RFC9180 (7933)

[RFC Errata System <[e-mail]>]

The following errata report has been submitted for RFC9180,
"Hybrid Public Key Encryption".

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You may review the report below and at:
https://www.rfc-editor.org/errata/eid7933

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Type: Technical
Reported by: Raul Siles <[e-mail]>

Section: 5.1

Original Text
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[In Section 5.1 the return value of KeySchedule<ROLE> reflects:]

return Context<ROLE>(key, base_nonce, 0, exporter_secret)

The ROLE template parameter is either S or R, depending on the role 
of sender or recipient, respectively. See Section 5.2 for a discussion 
of the key schedule output, including the role-specific Context 
structure and its API.


Corrected Text
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[In Section 5.1 the return value of KeySchedule<ROLE> reflects:]

return Context<ROLE>(key, base_nonce, 0, exporter_secret)

The ROLE template parameter is either S or R, depending on the role 
of sender or recipient, respectively. The third field in the 
Context<ROLE> refers to the sequence number, that is initialised with 
a 0 value. See Section 5.2 for a discussion of the key schedule output,
including the role-specific Context structure and its API, and the 
usage of the sequence number.


Notes
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In Section 5.1 the return value of KeySchedule<ROLE> reflects:

return Context<ROLE>(key, base_nonce, 0, exporter_secret)

I'm assuming the "0" value (in the third field of the Context<ROLE>) refers to the sequence number, with an initialisation value of 0, that is mentioned in Section 5.2, but the RFCs does not include details about the meaning of this third field and value.

I suggest to clarify in section 5.1 the meaning of that 0 value and field, and add a reference to section 5.2 with all the details about the sequence number.

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RFC9180 (draft-irtf-cfrg-hpke-12)
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Title               : Hybrid Public Key Encryption
Publication Date    : February 2022
Author(s)           : R. Barnes, K. Bhargavan, B. Lipp, C. Wood
Category            : INFORMATIONAL
Source              : Crypto Forum Research Group
Stream              : IRTF
Verifying Party     : IRSG