Abstract: A method of activating a function such as unlocking a mobile telephone keypad by an instruction sequence {xi, . . . , xn} of a length n given to a user, who validates the sequence to activate the function. The instruction sequence is determined randomly, and for each instruction xi, the method includes: sending an instruction xi to the user; receiving a response yi from the user; analysis for validation of instruction xi; instruction xi is said to be validated when yi is a valid response for xi and the time elapsed between the sending of xi and the receipt of yi is shorter than a set period ?i; if instruction xi is not validated then the function is not activated; sending the next instruction, if any, after validation of xi; activating the function when at least the last instruction sent is validated.

Abstract: A method of activating a function such as unlocking a mobile telephone keypad by an instruction sequence {x1, . . . , xn} of a length n given to a user, who validates the sequence to activate the function. The instruction sequence is determined randomly, and for each instruction xi, the method includes: sending an instruction xi to the user; receiving a response yi from the user; analysis for validation of instruction xi; instruction xi is said to be validated when yi is a valid response for xi and the time elapsed between the sending of xi and the receipt of yi is shorter than a set period ?i; if instruction xi is not validated then the function is not activated; sending the next instruction, if any, after validation of xi; activating the function when at least the last instruction sent is validated.