RFC 4880, "OpenPGP Message Format", November 2007

Note: This RFC has been obsoleted by RFC 9580

Note: This RFC has been updated by RFC 5581

Errata ID: 2215
Status: Rejected
Type: Editorial
Publication Format(s) : TEXT
Reported By: Constantin Hagemeier
Date Reported: 2010-04-28
Rejected by: Sean Turner
Date Rejected: 2010-07-20

Section 5.2.3.1. says:

   An implementation SHOULD ignore any subpacket of a type that it does
   not recognize.

   Bit 7 of the subpacket type is the "critical" bit.  If set, it
   denotes that the subpacket is one that is critical for the evaluator
   of the signature to recognize.  If a subpacket is encountered that is
   marked critical but is unknown to the evaluating software, the
   evaluator SHOULD consider the signature to be in error.

It should say:

   Bit 7 of the subpacket type is the "critical" bit.  If set, it
   denotes that the subpacket is one that is critical for the evaluator
   of the signature to recognize.  If a subpacket is encountered that is
   marked critical but is unknown to the evaluating software, the
   evaluator SHOULD consider the signature to be in error.

   An implementation SHOULD ignore any subpacket of a type that it does
   not recognize.

Notes:

The explanation for recognizing should come before recognizing is used.
--VERIFIER NOTES--
The existing text explains the rule of thumb, and then the exception. The suggestion would be more confusing than the original.

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