The possibility of making the Internet accessible via mobile telephones has generated an important opportunity for electronic commerce. Nevertheless, some deficiencies deter its mass acceptance in e-commerce applications. In order to speed up the information delivery, the use of brokerage systems constitutes an interesting solution. In this paper we review the problem of certificate validation in m-commerce transactions and we present an architecture where a broker is used as OCSP responder for the certificate validation. A modification over OCSP called -OCSP is also proposed as a way to reduce the computational load and the bandwidth requirements of OCSP which is specially desirable in the wireless environment. The ASN.1 add-on for -OCSP that makes it inter-operable with the standard OCSP is defined and the behaviour of -OCSP compared to standard OCSP is evaluated.