On Tue, May 20, 2008, Massimiliano Ziccardi wrote:
> I'm sure OpenSSL is able to parse more than one counter signature per
> signature.
>
> Can pleas some OpenSSL expert tell me how to do it? I think the code I sent
> in the previous
> e-mail should be close to the solution. I just need to know how to get the
> other counter signatures
> (I already did in Java with Bouncycastle, and it has been straightforward).
>
> I've searched through the net for some documentation, but, as stated on the
> site, the OpenSSL documentation
> is very incomplete, and I couldn't find any useful information.
>
Unfortunately the attribute handling functions are undocumented at present.
They opearate in a manner similar to the documented X509_NAME functions
though.
This is an outline of what you do....
If you call PKCS7_get_attributes() you will get back a
STACK_OF(X509_ATTRIBUTE). Using that you can look through it using the
attribute utility functions.
int X509at_get_attr_by_NID(const STACK_OF(X509_ATTRIBUTE) *x, int nid,
int lastpos);
You loop round calling X509at_get_attr_by_NID() to retrieve the index of each
countersignature attribute, you get -1 when no more can be found. You set
lastpos to the last index or -1 initially.
For each index you can get the corresponding attribute with:
X509_ATTRIBUTE *X509at_get_attr(const STACK_OF(X509_ATTRIBUTE) *x, int loc);
Then for each X509_ATTRIBUTE you can retrieve the count of attributes with
X509_ATTRIBUTE_count(). Then each individual using:
void *X509_ATTRIBUTE_get0_data(X509_ATTRIBUTE *attr, int idx,
int atrtype, void *data);
You set idx to the index of each one (starting from zero) atrtype to
V_ASN1_SEQUENCE and you get back an ASN1_STRING structure or NULL if the type
isn't a SEQUENCE: that shouldn't happen unless the countersignature is
malformed.
The for each string you parse the countersignature as before.
Steve.
--
Dr Stephen N. Henson. Email, S/MIME and PGP keys: see homepage
OpenSSL project core developer and freelance consultant.
Homepage: http://www.drh-consultancy.demon.co.uk
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