RE: Time Stamping: comments on nonce field

[Robert Zuccherato <robert.zuccherato@xxxxxxxxxxx>]

My comments are below:

> ----------
> From: 	Juan G. de la Vega[SMTP:jgonzalez@fnmt.es]
> Sent: 	Wednesday, April 07, 1999 5:39 AM
> To: 	ietf-pkix@imc.org
> Subject: 	Time Stamping: comments on nonce field
> 
>         First of all, the declaration of this field in the request and
> token is somehow incoherent, while the nonce is mandatory in TimeStapReq
> (it is not declared OPTIONAL), the TimeStampTokenīs nonce is OPTIONAL but
> it is stated that "...must be present if the similar field in TimeStampReq
> is present..." and hence the clause OPTIONAL is meaningless and confusing
> for this field shall always be present. 
> 
As I have said in the past, this was a mistake that I made because I did not
manage to fully include support for TSA production of a "signed time".  This
would be a token which does not include a nonce or message imprint.  TSA's
could produce these tokens and make them available (for example on a
website) for anyone who wants to obtain them.  This will be rectified in the
upcoming draft.

> I would suggest this field to be declared OPTIONAL both in the request and
> token or better deleted if we take into account the following:
>  
>     As far as I understand, a nonce value is present in the request and
> token in order for the requester to be able to match the responses from
> the TSA with her requests when using an asynchronous transport. It can be
> argued that such functionality should be left to the transport layer when
> required, but furthermore I must say that the nonce is not necessary since
> matching can be performed using the "messageImprint" field.
> 
Actually, the reason that the nonce is there and mandatory is to prevent
replay attacks.  Someone else could have obtained a time stamp on the data
before your request.  Thus, it is possible that the time stamp you received
is not "fresh".  Without a nonce, determining the freshness of the timestamp
is difficult.

	Robert.