Subject: RE: Countersignature Attribute

From: "Jim Schaad (Exchange)" <[email-masked]>
Date: Tue, 15 Sep 1998 14:41:01 -0700

I don't know about other products, but Outlook and OE tooke the approach of
ignoring countersignatures.
 
jim

-----Original Message-----
From: Russ Housley [mailto:[email-masked]]
Sent: Tuesday, September 15, 1998 1:40 PM
To: [email-masked]
Cc: [email-masked]; [email-masked]
Subject: Re: Countersignature Attribute

John:

Prior to getting this note, I took a stab at revisions to the same section
of text.  I do not know how S/MIME v2 implementations handle
countersignatures, but I took the opposite approach that you did.  I was
trying to ensure that current implemntations would all conform.

Here is what I wrote:

A countersignature attribute can have multiple attribute values.  The syntax
is defined as a SET OF AttributeValue, and there must be one or more
instances of AttributeValue present.

The UnsignedAttributes syntax is defined as a SET OF Attributes.  The
UnsignedAttributes in a signerInfo may include multiple instances of the
countersignature attribute.

The fact that a countersignature is computed on a signature value means that
the countersigning process need not know the original content input to the
signing process.  This might have efficiency advantages, but it also has
security disadvantages.  Therefore, countersigners must validate the
signature value prior to signing it.  This validation requires processing of
the original content.

A countersignature, since it has type SignerInfo, can itself contain a
countersignature attribute.  Thus it is possible to construct arbitrarily
long series of countersignatures.

Russ

At 11:56 AM 9/15/98 -0400, John Pawling wrote:
>Peter (and friends),
>
>I agree with your recommendation.  This results in a change to my comment
to
>CMS-06 to read as follows:
>
>5) Sec 11.4, Countersignature: Please change as follows:
>
>OLD: "A countersignature attribute can have multiple attribute values."
>
>NEW: "The UnsignedAttributes syntax is defined as a SET OF Attribute.  
>The UnsignedAttributes in a signerInfo MUST NOT include multiple 
>instances of the countersignature attribute.  The Attribute syntax defines 
>attrValues as a SET OF AttributeValue.  A countersignature attribute 
>MAY include one or more instances of AttributeValue.  There MUST NOT 
>be zero instances of AttributeValue present in the attrValues SET
>OF AttributeValue."
>
>Does anybody disagree with this recommendation???
>
>- John Pawling
>

---

From: Dr Stephen Henson <[email-masked]>
Date: Tue, 15 Sep 1998 23:02:58 +0100

> ignoring countersignatures.

Jim, 

I seem to recall there are functions in MS CryptoAPI for adding
countersignatures. I haven't used them myself but can you comment on
whether multiple countersignatures can be added and if so what format it
uses?

Steve.
-- 
Dr Stephen N. Henson. UK based freelance Cryptographic Consultant. 
For info see homepage at http://www.drh-consultancy.demon.co.uk/
Email: [email-masked]
PGP key: via homepage.