On Wed, 28 May 2003, Yaniv Kaul wrote:
> I'm trying to add ASN.1 certificate parsing to Ethereal. I'll start with
> SSL, then do something generic, which can be used by SSL, SSH, IKE and
> possibly others I'm not aware of.
> However, I'm having problem using asn1_id_decode(), as for ID=0 it only
> moves asn1->offset 1 byte ahead, instead of 2 bytes. If I 'manually'
> move it, everything's ok.
> Here's what I'm trying to dissect, I'd appreciate if knowledgable people
> could help me out here:
> 30 82 02 DF (Certificate SEQUENCE, length 0x02DF)
> 30 82 01 C7 (TBSCertificate SEQUENCE, length 0x1C7)
> A0 03 (ID=0, length 3 - this is where I'm stuck)
> 02 01 02 (Integer, length =1, value =2 - which is the Version
> number of the certificate - val=2 means X.590v3)
RFC 3280 says that a TBSCertificate is laid out as follows:
TBSCertificate ::= SEQUENCE {
version [0] EXPLICIT Version DEFAULT v1,
serialNumber CertificateSerialNumber,
signature AlgorithmIdentifier,
issuer Name,
validity Validity,
subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version MUST be v2 or v3
subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version MUST be v2 or v3
extensions [3] EXPLICIT Extensions OPTIONAL
-- If present, version MUST be v3
}
Version ::= INTEGER { v1(0), v2(1), v3(2) }
I think the sequence "A0 03 02 01 02" is
A0 03 - EXPLICIT tag [0] (context | constructed | 0), length = 3
02 01 02 - Version INTEGER, length = 1, value = 2
> The relevant piece of my code is:
> ret = asn1_id_decode(&hnd, &cls, &con, &tag);
> if(ret == ASN1_ERR_NOERROR) {
> proto_tree_add_text(subtree, tvb, cert_len, 2, "ID %d",tag);
> cert_len += 2;
> hnd.offset++; /* My much needed hack! */
>
>
> I believe the problem is in asn1.h, in line 191:
> if (*tag == 0x1F) {
>
>
> Any help will be greatly appreciated.
> Relevant RFC is 3280, if anyone's interested.
>
> Y.
>
>
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