Subject: [MSEC] Signature Payload

From: Uri Meth <[email-masked]>
Date: Fri, 21 Feb 2003 10:00:55 -0500

In the modified GSAKMP specification which is set to be released soon
there is a modification in the definition of the Signature Payload.
Here I will present the old text and the new text and then define the
reason for this modification.

Old Signature Payload Text:
The Signature Payload contains data generated by the digital signature
function.  The digital signature covers the Signature Payload Span and the
Signature Payload up to the Signature Data.  The exception to this is if
the signature algorithm used is DSS with ASN.1/DER encoding.  Due to the
variable length of a DER encoding, the signature span across the signature
payload itself only extends up to the signature data length field, not the
signature data.

New Signature Payload Text:
The Signature Payload contains data generated by the digital signature
function.  The digital signature covers the Signature Payload Span and the
Signature Payload up to the Signature Data Length.  

Rational:
There really is no extra benefit to signing over the signature data
length field, therefore there is no reason to make an exception case.
By not signing over this field, we do not open ourselves to any attacks.
If this value is modified, the signature will not verify because you
would then have a incorrect length for the signature value received and
would never be able to generate a correct signature for comparison
purposes.

Any and all comments are always welcome.

UM
-- 
Uri Meth                            (410) 872 - 1515 x233 (voice)
SPARTA, Inc.                        (410) 872 - 8079      (fax)
7075 Samuel Morse Drive             [email-masked]
Columbia, MD 21046

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