Hi Steven,
I would like to know point 2.
- Sravan
Steven Reddie wrote:
I'm sure someone will jump in if they see a mismatch in your question and my
answer. In the meantime let's break it down. Are you:
1. Looking at some existing data model expressed in ASN.1 (such as X.509 or
OCSP) and are curious about when you need to worry about explicit vs
implicit?
2. Curious about when to use explicit vs implicit when specifying a data
model in ASN.1?
3. Something else?
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of sravan
Sent: Thursday, 8 September 2005 3:37 PM
To: openssl-users@openssl.org
Subject: Re: OCSP, Nonce and the requestExtensions
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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