Re: [Technical Errata Reported] RFC3029 (6444)

Erwann:
> 
> Le sam. 27 févr. 2021 à 08:45, Russ Housley <[email protected] <mailto:[email protected]>> a écrit :
> I guess I should have held off on reporting this ASN.1 error.  Once I corrected it, I discovered two errors that I do not know how to fix.
> 
> There is an implementation somewhere because Appendix F contains examples.  I do not know how the implementer got around these two problems.
> 
> 
> PROBLEM 1:
> 
> CertEtcToken ::= CHOICE {
>      certificate                  [0] IMPLICIT Certificate ,
>      esscertid                    [1] ESSCertId ,
>      pkistatus                    [2] IMPLICIT PKIStatusInfo ,
>      assertion                    [3] ContentInfo ,
>      crl                          [4] IMPLICIT CertificateList,
>      ocspcertstatus               [5] IMPLICIT CertStatus,
>      oscpcertid                   [6] IMPLICIT CertId ,
>      oscpresponse                 [7] IMPLICIT OCSPResponse,
>      capabilities                 [8] SMIMECapabilities,
>      extension                    Extension{{ExtensionSet}}
> }
> 
> CertEtcToken is a CHOICE with tags 0 through 8, but CertStatus CHOICE with tags 0 through 2.  You cannot nest a CHOICE in another CHOICE is the IMPLICIT tags overlap.
> 
> The use of EXPLICIT tagging would have solved the problem, but the authors clearly preferred IMPLICIT tags.
> 
> Here, it's easy. The outermost IMPLICIT tag is transformed into an EXPLICIT one by the ASN.1 compiler (it will probably emit a warning, though).

Yes, I am aware of that possibility of fixing the specification, but it is unclear what an implementer would do with a ASN.1 module with compilation errors, or a warning that inserts a EXPLICIT.

> 
> PROBLEM 2
> 
> DigestInfo ::= SEQUENCE {
>     digestAlgorithm   DigestAlgorithmIdentifier,
>     digest            Digest
> }
> 
> Data ::= CHOICE {
>       message           OCTET STRING ,
>       messageImprint    DigestInfo,
>       certs             SEQUENCE SIZE (1..MAX) OF
>                             TargetEtcChain
> }
> 
> DigestInfo is a SEQUENCE, and certs is a SEQUENCE, so the two have the same tag.  A recipient cannot tell which one the sender intended.
> 
> For this one, there's clearly no solution. Tagging would have solved it (any kind of tagging mode), but it's missing.

Indeed, at lease one of the SEQUENCE needs a tag.

Russ

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