Abstract: The invention relates to a method for securing a contactless service transaction, said service (11) being stored in the mobile terminal (10), said transaction involving the mobile terminal, a contactless reader (12) and a remote server (13), said server storing at least one piece of data and/or sensitive function of the service, said terminal comprising a security module (14), said method being characterised in that the terminal also stores a contactless security application (15) and that it comprises: receiving (E41) a first value (?) for determining a session key; receiving (E49) a second value for determining a session key (?) and a first one-time password (OTPin); sending (E58) the second value for determining a session key and a message (MAC) for authenticating at least the first password, intended for being verified by the reader, said first and second determination values being used to calculate (E50, E61) a session key (Ksess) intended for being used to secure the exchanges.

Abstract: The invention relates to a method for securing a contactless service transaction, said service (11) being stored in the mobile terminal (10), said transaction involving the mobile terminal, a contactless reader (12) and a remote server (13), said server storing at least one piece of data and/or sensitive function of the service, said terminal comprising a security module (14), said method being characterised in that the terminal also stores a contactless security application (15) and that it comprises: receiving (E41) a first value (?) for determining a session key; receiving (E49) a second value for determining a session key (?) and a first one-time password (OTPin); sending (E58) the second value for determining a session key and a message (MAC) for authenticating at least the first password, intended for being verified by the reader, said first and second determination values being used to calculate (E50, E61) a session key (Ksess) intended for being used to secure the exchanges.