RFC 5280, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", May 2008

Note: This RFC has been updated by RFC 6818, RFC 8398, RFC 8399, RFC 9549, RFC 9598, RFC 9608, RFC 9618

Errata ID: 6830
Status: Reported
Type: Technical
Publication Format(s) : TEXT
Reported By: Corey Bonnell
Date Reported: 2022-02-02

Section Appendix A.1 says:

-- Note - upper bounds on string types, such as TeletexString, are
-- measured in characters.  Excepting PrintableString or IA5String, a
-- significantly greater number of octets will be required to hold
-- such a value.  As a minimum, 16 octets, or twice the specified
-- upper bound, whichever is the larger, should be allowed for
-- TeletexString.  For UTF8String or UniversalString at least four
-- times the upper bound should be allowed.

It should say:

-- Note - upper bounds on string types, such as TeletexString, are
-- measured in characters.  Excepting PrintableString or IA5String, a
-- significantly greater number of octets will be required to hold
-- such a value.  As a minimum, 16 octets, or twice the specified
-- upper bound, whichever is the larger, should be allowed for
-- TeletexString.  For UTF8String or UniversalString, four
-- times the upper bound should be allowed.

Notes:

"at least four times" is likely a holdover from RFC 3280, as the same text exists in that RFC. In RFC 3280, the definition of UTF-8 in UTF8String was normatively referencing RFC 2279, which allowed for a maximum of 6 octets to represent a single Unicode character in UTF-8. However, RFC 5280 was updated to normatively reference RFC 3629, which restricts the allowed set of characters in a UTF-8 string to match those allowed in UTF-16 (i.e., the BMP and 16 supplementary planes as opposed to all 32k planes). As a result, the maximum length for a single RFC 3629 UTF-8 character is 4 octets, rendering the guidance of "at least four times" wholly unnecessary; "four times" is sufficient in all cases.

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