Abstract: A dynamic authentication system for digital TV, the system comprising a mobile telephone to be operated by an end-user in connection with a digital TV receiver, the mobile phone being adapted for the short message systems SMS, a tamper resistant module, such as a user smart card in the digital TV receiver being adapted to generate a dynamic authentication code to be shown on the television screen (TV), the end-user reads and enters said authentication code into his mobile phone, said authentication code and application specific data thereafter being sent via SMS to an application server containing or making use of an authentication code validation system, and depending on whether among others the authentication code is acceptable, grants or conducts a certain service for the end-user.