RFC 6376, "DomainKeys Identified Mail (DKIM) Signatures", September 2011

Errata ID: 5070
Status: Verified
Type: Technical
Publication Format(s) : TEXT
Reported By: Chris Newman
Date Reported: 2017-07-15
Verifier Name: Barry Leiba
Date Verified: 2019-04-30

Section 3.2 says:

   tag-spec  =  [FWS] tag-name [FWS] "=" [FWS] tag-value [FWS]
   tag-name  =  ALPHA *ALNUMPUNC
   tag-value =  [ tval *( 1*(WSP / FWS) tval ) ]
                     ; Prohibits WSP and FWS at beginning and end

It should say:

   tag-spec  =  [FWS] tag-name [FWS] "=" [FWS] [tag-value [FWS]]
   tag-name  =  ALPHA *ALNUMPUNC
   tag-value =  tval *( 1*(WSP / FWS) tval )
                     ; Prohibits WSP and FWS at beginning and end

Notes:

The ABNF in the document permits two FWS rules to appear in the row. This results in permitting a line with only whitespace in the header which falls into obsolete syntax in RFC 5322 (Appendix B rule 12). The corrected text disallows this by eliding the second FWS when the tag-value is empty/omitted.

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