RE: Correct definition of ContentInfo in CMS-10

["Russ Housley" <[e-mail]>]

Chris:

In PKCS#7 v1.5, ContentInfo was used as the outer wrapper (around
SignedData, EnvelopedData, etc) as well as the wrapper around the content
being protected.  In CMS, two different ASN.1 types are used for the two
different wrappers.  ContentInfo remains the outer wrapper.  There is no
need for such a wrapper without a protecting content such as SignedData,
EnvelopedData, etc., therefore the ContentInfo content should not be
optional.  The EncapsulatedContentInfo is the wrapper for the content being
protected.  To support a SignedData for distribution of certificates and
CRLs without any content (this approach is used in many products for
certificate user enrollment), EncapsulatedContentInfo has an OPTIONAL
content.

Russ

-----Original Message-----
From:	[e-mail] [mailto:[e-mail]] On Behalf
Of Bonatti, Chris
Sent:	Monday, February 22, 1999 9:42 AM
To:	William Ottaway; '[e-mail]'; Russ Housley
Subject:	Re: Correct definition of ContentInfo in CMS-10

    I would submit that the 'content' field in the General Syntax section is
correct.  The instance of OPTIONAL in the appendix must be a copy artifact
from the 'EncapsulatedContentInfo', in which the 'content' field is
correctly optional.  I can see no legitimate use of CMS in which you would
send only a 'contentType' OID.  Even if someone were sending a "detached
content" in a separate body part, either MIME or X.400 mail systems are
perfectly capable of attaching a content types for that information without
utilizing this structure.

Russ,

    Browsing through my historical archive of now "non-existent" I-Ds, I see
that the OPTIONAL tag seems to have fallen out of the General Syntax
starting in version 3 of CMS.  Do you remember the reasoning behind the
change?

Chris



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 |  International Electronic Communication Analysts, Inc.      |
 |  Christopher D. Bonatti             15309 Turkey Foot Road  |
 |  Principal Engineer              Darnestown, Md 20878-3640  |
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____________________

William Ottaway wrote:

> Within the body of CMS 10 ContentInfo is defined as : -
>
> ContentInfo ::= SEQUENCE {
>         contentType ContentType,
>         content [0] EXPLICIT ANY DEFINED BY contentType }
>
> However, in the appendix ContentInfo is defined as : -
>
> ContentInfo ::= SEQUENCE {
>      contentType ContentType,
>      content [0] EXPLICIT ANY DEFINED BY contentType OPTIONAL }
>
> I assume the one within the body (i.e. content not optional) is correct.
>
> Bill.
>
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> ____________________________________________________
> William Ottaway BSc Hons CEng MBCS,
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>
> All opinions are my own.