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Re: Creating ASN.1 definitions structures from memory-buffered ASN.1 des

From: Simon Josefsson
Subject: Re: Creating ASN.1 definitions structures from memory-buffered ASN.1 description
Date: Wed, 20 Jun 2012 08:35:05 +0200
User-agent: Gnus/5.130006 (Ma Gnus v0.6) Emacs/23.3 (gnu/linux)

"Yuriy V. Snegirev" <address@hidden> writes:

> Hi!
> First we would like to thank all developers, contributors and
> maintainers of libtasn1 for providing a wonderful library, which, in
> turn, provides possibilities to deal with DER-encoded data and ASN.1
> descriptions in runtime, without need to recompile the entire
> applications when some definitions change.
> However, we discovered, that some capabilities were absent from the
> library, one of which being the ability to process memory-cached ASN.1
> descriptions. So, in order to accomplish this, we modified libtasn a
> bit. The patch is attached.

Hi!  Thanks, this seems quite useful.  To be able to apply it, you will
need to sign a copyright assignment form.  I have sent it privately.
I'll review the code in detail later.

> Also, we got used to call asn1_get_length_der on a part of DER-encoded
> piece of data in order to acquire the size of entire piece. But,
> starting from commit 3873c6a49122e3f15901646e072938557acd3f8e (" Added
> overflow detection that does not depend on specific compiler, and
> asn1_get_der_length() verifies the length of the input data in small
> numbers as well.") this is no longer possible. So, the question is as
> follows: is there a way to achieve the same result now?

You may want to write another function for this... using the old
function on incomplete structures was error-prone.  Just make sure the
new function is safe, it is rather tricky code.


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