[openssl-users] Extract content of DER-encoded package by OID

Justin Mogannam jmogannam at arkhamtechnology.com
Tue Jul 18 22:06:48 UTC 2017

I have a signedData package that contains an encryptedKeyPackage
(specifically OID 2.16.840., 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. 

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