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[ietf-dkim] Base-04 // ABNF cruft & errors

2006-07-21 12:32:50
2.3  White Space

ALPHA, DIGIT, SP, CRLF, HTAB, WSP are defined in RFC4234.

There is no reason to reference the WSP definition in RFC2822.


The RFC2822 FWS ABNF definition carries some cruft.

obs-FWS         =       1*WSP *(CRLF 1*WSP)     ; obsolete RFC822 text
FWS             =       ([*WSP CRLF] 1*WSP) / obs-FWS

Is there a reason to permit multiple CRLFs? To obsolete support, the definition should be removed after 5 years of being declared obsolete.

FWS should be redefined as Revised FWS such as:

R-FWS           =       ([*WSP CRLF] 1*WSP)     ; revised


3.4.6  Canonicalization Examples (INFORMATIVE)

This uses an undefined value TAB. HTAB for horizontal as opposed to vertical tab is defined in RFC4234. substitute TAB with HTAB for the value to be defined in the ABNF reference.


After all the concern about isolated CR and LF, this definition stands out as being wrong.

SWSP =   CR / LF / WSP   ; streaming white space

Define as:

SWSP    =       WSP / CRLF


Also previously noted, the ABNF for sub-domain referenced from RFC2821 is insufficient. This definition does not limit the length of the label.

hyphen = %x2D ; "-"
ldh = ALPHA | DIGIT | hyphen
let-dig = ALPHA | DIGIT
sub-domain =  let-dig [*61(ldh) let-dig]

The definition found in STD13 excludes an email-address such as abuse1(_at_)3com(_dot_)com based upon the recommended ABNF for a label. The best solution is to repair the ABNF for sub-domain.

-Doug




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