Hi Steven,
I am sorry to say that I couldn't get what you have explained in your
mail. I don't say that it is a problem in your explaination but I can't
understand this(may be a problem in my comprehension). Any one out there
who can explain this plz help us out...
- Sravan
Steven Reddie wrote:
I meant to say that I don't know of any specific reason other than not
changing the underlying type. I imagine that not changing the underlying
type can be important/helpful in some situations. An example being an
encoded certificate as a member of some other structure. In order to "hand"
the certificate portion of the DER to an X.509 decoder an implicit tag would
have to changed to the universal tag expected of the certificate. For
verifying the signature it would also be necessary to "correct" an implicit
tag. Using an explicit tag instead means that the underlying object is
still a standalone certificate.
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Steven Reddie
Sent: Thursday, 8 September 2005 2:17 PM
To: openssl-users@openssl.org
Subject: RE: OCSP, Nonce and the requestExtensions
When working with encodings of an existing data model then the use of
implicit vs explicit comes down to what the designers specified. ie. for
interoperability you can't work against the specification.
When designing a data model with ASN.1 I don't know of any specific reason
for using one over the other. Explicit tags wrapper the underlying object
and as such add a little bloat but leave the underlying encoded object
unchanged. Implicit tags replace the underlying tag in the encoding,
avoiding the little bloat, but altering the encoded representation of the
underlying object.
For example, the INTEGER zero is encoded in DER as 02 01 00. Applying a
context-specific tag of 2 results in:
Implicit: 82 01 00
Explicit: 82 03 02 01 00
Regards,
Steven
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of sravan
Sent: Thursday, 8 September 2005 1:55 PM
To: openssl-users@openssl.org
Subject: Re: OCSP, Nonce and the requestExtensions
Hi Steven and others,
i have a doubt regd these tags in ASN1:
when do we use implicit tags & when do we use explicit tags?
i have read the 'layman's guide to a subset of ASN.1, BER & DER' but it
seems i didn't get the exact difference b/n the two types of tags - in the
sense of exact context in which each of these types of tags are used.
bye & thnx
- sravan
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