The problem of securing data communications in civil and commercial space missions has been debated within the Security Working Group of the Consultative Committee for Space Data Systems since several months. In the context of Telecommand transmissions, the interest is mainly focused on authentication, more than encryption. The object of this paper is to investigate the applicability of a standard scheme, Digital Signature Algorithm with SHA-1, to the authentication of Telecommand segments, and to discuss the pros and cons related to its adoption in such a peculiar context.