Re: ASN.1 PKCS7 certificate decoding help

On Sat, Jan 21, 2023 at 5:47 AM James Chapman <[email protected]> wrote:
>
> New subscriber and CryptoPP user list here. I'm hoping you can assist me and point me in the right direction. I'm trying to read information from PE file signing certificates which are typically in PKCS#7 format. I've extracted the certificate structure OK, but now I'm trying to use CryptoPP to extract information from the certificates.
>
> I've used certutil to dump an ASN structure from acrobat.exe (for easy reference I've placed it at the bottom of this email).
>
> So far, I've got this:
>
>             CryptoPP::VectorSource vs(certData.certificate, true);
>             CryptoPP::BERSequenceDecoder p7b(vs);
>             CryptoPP::BERSequenceDecoder outerObject(p7b, CryptoPP::OBJECT_IDENTIFIER);
>
> Anything I try after this throws.

What was the exception? The ASN.1 gear likely does not know about OIDs
1.2.840.113549.1.7.2, 2.16.840.1.101.3.4.2.1,
1.2.840.113549.1.9.16.1.4 and friends. But the exception should tell
you the problem.

> I presume I need to read the OPTIONAL somehow and then from there process the SEQUENCE. In fact, I suspect the best approach would be to somehow enumerate the SEQUENCE sections and then process those individually, but with the tools available to me in CryptoPP's ASN section I've not been able to work out how to do that yet :-(
>
> I'm probably missing something obvious (I should point out that I'm new to ASN1 too). Any guidance, words of wisdom or even examples would be greatly appreciated.
>

Also see https://www.cryptopp.com/wiki/X509Certificate . It is an
example of parsing X.509 certificates.

Jeff

> 0000: 30 82 17 25                               ; SEQUENCE (1725 Bytes)
> 0004:    06 09                                  ; OBJECT_ID (9 Bytes)
> 0006:    |  2a 86 48 86 f7 0d 01 07  02
>          |     ; 1.2.840.113549.1.7.2 PKCS 7 Signed
> 000f:    a0 82 17 16                            ; OPTIONAL[0] (1716 Bytes)
> 0013:       30 82 17 12                         ; SEQUENCE (1712 Bytes)
> 0017:          02 01                            ; INTEGER (1 Bytes)
> 0019:          |  03
> [...]

-- 
You received this message because you are subscribed to the Google Groups "Crypto++ Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
To view this discussion on the web visit https://groups.google.com/d/msgid/cryptopp-users/CAH8yC8k4spB09YPRU4qjB1_JfwOgbYz7T7GtztgLPJwoL8Xa6Q%40mail.gmail.com.