Yes, but you realise that instead of:
y OCTET STRING -- contains X
you can now write
y OCTET STRING (CONTAINING X)
as formal syntax.
John L
Paul Long wrote:
>
> Rajul,
>
> Okay, thanks. So I think you're answer to my first question is, yes. :-)
>
> Also, given X:
>
> X ::= SEQUENCE {
> a INTEGER, -- stuff...
> b BOOLEAN
> }
>
> I believe that Z1:
>
> Z1 ::= SEQUENCE {
> y TYPE-IDENTIFIER.&Type (X)
> }
>
> encodes in PER exactly like Z2:
>
> Z2 ::= SEQUENCE {
> y OCTET STRING -- contains X
> }
>
> True?
>
> Paul Long
> ipDialog, Inc.
>
> > -----Original Message-----
> > From: Rajul Gupta [mailto:[EMAIL PROTECTED]]
> > Sent: Monday, June 24, 2002 4:13 PM
> > To: [EMAIL PROTECTED]
> > Cc: [EMAIL PROTECTED]
> > Subject: Re: [ASN.1] TYPE-IDENTIFIER.&Type
> >
> >
> > Hi Paul,
> >
> > (X) is a type constraints here, and it says that "y" MUST be of type "X"
> > only. Syntactically, this is equivalent to
> >
> > Z ::= SEQUENCE {
> > y X
> > }
> >
> > However, this kind of syntax (your syntax) is useful in case of PER. PER
> > always doesn't have length encoded, but while encoding open
> > types, PER puts
> > a length wrapper also. So if you are using PER, then at the decoding side
> > you can easily find out the length of encoded open type value, without
> > knowing it's type.
> >
> > Usually this type of construct is useful for security fields. Using length
> > wrapper you can easily find out the length of security data and leave this
> > data unwrapped and unprocessed in your application, and pass it to other
> > application or function, where this security data is used.
> >
> > I hope this answer could be helpful for you.
> >
> > Rajul
> >
> > > I've put it off too long. Now it's time for me learn this ".&" stuff. Is
> > y,
> > > below, encoded in PER as an open type that contains an encoding of X? Is
> > > that all there is to it?
> > > Also, what syntactical role does the "(X)" play? Is
> > > this a constraint and otherwise y could be encoded as an open
> > type of any
> > > type?
> > > X ::= SEQUENCE {
> > > a INTEGER, -- stuff...
> > > b BOOLEAN
> > > }
> > >
> > > Z ::= SEQUENCE {
> > > y TYPE-IDENTIFIER.&Type (X)
> > > }
> > >
> > > Paul Long
> > > ipDialog, Inc.
> > >
> > >
> > >
> >
> >
--
Prof John Larmouth
Larmouth T&PDS Ltd
(Training and Protocol Development Services)
1 Blueberry Road
Bowdon [EMAIL PROTECTED]
Cheshire WA14 3LS Tel: +44 161 928 1605
England Fax: +44 161 928 8069
