Extract content of DER-encoded package by OID

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Extract content of DER-encoded package by OID

jMo925
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Hello,
I have a signedData package that contains an encryptedKeyPackage (specifically OID 2.16.840.1.101.2.1.2.78.2, aka id-ct-KP-encryptedKeyPkg) that I want to extract from it. I am somewhat able to extract the sequence that contains this data via the OpenSSL command line:

$ openssl asn1parse -in <my_pkg.der> -inform DER -strparse <hard-coded offset I computed>

However, I am looking for the OpenSSL calls to do the same thing, ideally extract package contents by its OID without having to know the offset (such that I can extract the data from any given package by that particular OID). How would I go about doing this? I've been looking endlessly into asn1.h and x509.h, and am able to somewhat parse the entire package into a structure, but I could use some guidance as to how to further break it down into parts. Thank you, and I hope to hear a response back soon.

PS: I wasn't able to subscribe to the mailing list... I pressed "subscribe" and I got the following response from the mail server every time I tried:
                   The mail system

<majordomo@openssl.org>: host mta.openssl.org[194.97.150.230] said: 550 5.1.1
    <majordomo@openssl.org>: Recipient address rejected: User unknown in
    virtual alias table (in reply to RCPT TO command)


I'm guessing the subscribe email address is out of order for now? I hope people/the mods are still able to see my post. Thanks!