OpenSSL::ASN1::ObjectId#sn

static VALUE
ossl_asn1obj_get_sn(VALUE self)
{
    VALUE val, ret = Qnil;
    int nid;

    val = ossl_asn1_get_value(self);
    if ((nid = OBJ_txt2nid(StringValueCStr(val))) != NID_undef)
        ret = rb_str_new2(OBJ_nid2sn(nid));

    return ret;
}