Question was how to retrieve those lists for any given certificate,
using currently supported OpenSSL APIs.

The lists of usage bits and extusage OIDs in any given certificate
are finite, even if the list of values that could be in other
certificates is infinite.

On 2021-07-16 06:44, Kyle Hamilton wrote:
Also, OIDs for extendedKeyUsage can be defined per-application, so
there's no way to compile a full list of them.

-Kyle H

On Fri, Jul 16, 2021 at 4:23 AM Viktor Dukhovni
<openssl-us...@dukhovni.org>  wrote:
On 15 Jul 2021, at 11:55 pm, SIMON BABY<simonkb...@gmail.com>  wrote:

I am looking for openssl APIs to get all the OIDs associated with user 
certificate Key usage extension. For example my sample Key usage extension from 
the certificate is below:
X509v3 extensions:
             X509v3 Key Usage: critical
                 Digital Signature, Key Encipherment

I am looking for the APIs used to get the OIDs associated with  Digital 
Signature and Key Encipherment from the certificate.
There are no keyUsage OIDs, the field is a bitstring:

    https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.3

       id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }

       KeyUsage ::= BIT STRING {
            digitalSignature        (0),
            nonRepudiation          (1), -- recent editions of X.509 have
                                         -- renamed this bit to 
contentCommitment
            keyEncipherment         (2),
            dataEncipherment        (3),
            keyAgreement            (4),
            keyCertSign             (5),
            cRLSign                 (6),
            encipherOnly            (7),
            decipherOnly            (8) }

There are OIDs in the extendedKeyUsage:

     https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.12



Enjoy

Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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