Extend CMS unit tests (pem/der conversions)

        let encrypt = CmsContentInfo::encrypt(&cert_stack, &input.as_bytes(), Cipher::des_ede3_cbc(), CMSOptions::empty())

            .expect("failed create encrypted cms");

        let encrypt = encrypt.to_der().expect("failed to create der from cms");

        let encrypted_der = encrypt.to_der().expect("failed to create der from cms");

        let encrypted_pem = encrypt.to_pem().expect("failed to create pem from cms");

        // decrypt cms message using private key cert

        let decrypt = CmsContentInfo::from_der(&encrypt).expect("failed read cms from der");

        // decrypt cms message using private key cert (DER)

        {

            let decrypt = CmsContentInfo::from_der(&encrypted_der).expect("failed read cms from der");

            let decrypt = decrypt.decrypt(&priv_cert.pkey, &priv_cert.cert).expect("failed to decrypt cms");

            let decrypt = String::from_utf8(decrypt).expect("failed to create string from cms content");

            assert_eq!(input, decrypt);

        }

        // decrypt cms message using private key cert (PEM)

        {

            let decrypt = CmsContentInfo::from_pem(&encrypted_pem).expect("failed read cms from pem");

            let decrypt = decrypt.decrypt(&priv_cert.pkey, &priv_cert.cert).expect("failed to decrypt cms");

            let decrypt = String::from_utf8(decrypt).expect("failed to create string from cms content");

            assert_eq!(input, decrypt);

        }

    }

}