Subject: [plasma] Verifying the signature of the LockBox.

From: Alan Borland <[email-masked]>
Date: Wed, 13 Mar 2013 10:21:20 +0000

[Boldon James classification: UNMARKED EXTERNAL]

When we open a message we have to determine if the message is a traditional S/MIME message or a Plasma message.  This is done by inspecting the CMS envelopedData layer looking for a Plasma LockBox. If the lockbox is found we verify the SignedData signature, but this got me thinking.  Should we verify just the integrity of the signature itself or should we also perform a full certificate path validation as well?   This would mean every user needs to trust a certificate from the Plasma Server (additional overhead - is this an issue?), but then if the Plasma Server is somehow compromised this would be a way of returning the error to the client.

I couldn't decide either way, at the moment we're doing a full certificate path validation.

Alan.

Alan Borland

Boldon James Limited, a QinetiQ company
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---

From: "Jim Schaad" <[email-masked]>
Date: Wed, 13 Mar 2013 08:44:07 -0400

It is my believe you should perform the full path verification.  If you
don't then you have no confidence in any of the signed attributes associated
with the signature such as the URL for the plasma server and thus go
someplace you don't want to and start the plasma protocol.

Jim

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Alan Borland
Sent: Wednesday, March 13, 2013 6:21 AM
To: [email-masked]'
Subject: [plasma] Verifying the signature of the LockBox.

When we open a message we have to determine if the message is a traditional
S/MIME message or a Plasma message.  This is done by inspecting the CMS
envelopedData layer looking for a Plasma LockBox. If the lockbox is found we
verify the SignedData signature, but this got me thinking.  Should we verify
just the integrity of the signature itself or should we also perform a full
certificate path validation as well?   This would mean every user needs to
trust a certificate from the Plasma Server (additional overhead - is this an
issue?), but then if the Plasma Server is somehow compromised this would be
a way of returning the error to the client.

I couldn't decide either way, at the moment we're doing a full certificate
path validation.

Alan.

Alan Borland

Mobile:        +44 (0)7810 556709
Direct:         +44 (0)1270 507841
Switch:        +44 (0)1270 507800
Email:          [email-masked]
Email (R):    [email-masked]
Web:           www.boldonjames.com