Hello,

I believe that the current code base does not support EnvelopedData with Elliptic Curve Cryptography (ECC) for CMS.
Would you be interested in a code contribution that would bring partial CMS ECC support as per rfc5753?

I could contribute some code that would essentially implement KeyAgreeRecipientInfoBuilder for KeyAgreeRecipientInfo (Kari).

It would not implement all the KeyAgreement algorithms mentioned in the RFC as I think that RustCrypto does not currently have all the primitive to fully support other KeyAgreement schemes (namely 'Co-factor' ECDH and 1-Pass ECMQV). As such it would mainly focus on EnvelopedData Using (ephemeral-static) ECDH with 'Standard' ECDH

A few initial prerequisite would be:

• ANSI-X9.63-KDF support - (Pending - I already opened a PR in KDFs Done in ANSI-X9.63-KDF KDFs#101)
• Missing OIDs from rfc5753 - I can open another issue here if there is interest (Pending Done in Add RFC5753 to const-oid #1546).

Thank you and let me know your thoughts,

Best,