How to generate a x.509 certificate with a Serial Number using openssl?

[Vishwamithra37]

So, I tried almost all the available methods on the internet, set_Serial number, create_serial number and other flags. But I'm unable to get a certificate with a serial number. And make it visible in the certificate field during signing of PDF using pyHanko.
Any help will be greatly appreaciated. :)
openssl req -newkey ec:<(openssl ecparam -name secp384r1) \ -x509 \ -sha256 \ -days 3650 \ -nodes \ -out example3.crt \ -keyout example3.key \ -set_serial 8787 \ -subj "/CA=65216895787/C=IN/ST=Telangana
I'm currently try thins, but it is not showing the serial number field.
On the same note, how to access specific fields in a cert using pyHanko, like if I want to access the ST field in my certificate, or the public key, is it possible? How?

• Question: How to extract the certificate fields seperately from a signature? That is, get the certificate.

[MatthiasValvekens]

You can supply your own interpolation values for text stamps / qr stamps using the appearance_text_params argument to sign_pdf and friends. You could use those to create %(st)s and %(serial)s parameters, if you'd want to.

As for how to extract the information to populate those variables from the certificate: have a look at the properties on this class in asn1crypto (that's also the one pyHanko uses internally). Getting the serial number is straightforward, but extracting a RDN segment like ST will require a bit more digging. You'll want to parse that out of the x509.Name structure that represents the certificate's subject. asn1crypto can help you with that as well.

[Vishwamithra37]

No like, I'm 100% sure pyHanko has this functionality, it displays the certificate details during the valistion code. So, umm, there is no other way but to use that library to parse the certificate indvidual data?

[MatthiasValvekens]

asn1crypto is a dependency of pyHanko, and the certificate objects that pyHanko passes around in its internal APIs are instances of x509.Certificate. In other words, you don’t have to install any additional libs :)