Systeme d'authentification analogique reciproque entre un terminal et une ligne de transmission

Claim 1

A system for authenticating a call by analog frequency signals lying in a first or data range of frequencies between a transmitter/receiver terminal and a communications line, the system being characterized in that it further includes a monitoring device connected in said line, and in that: said terminal includes means for generating authentication frequency signals in addition to said communications signals with a periodicity T while a call is in progress, said authentication signals having frequencies lying in a second frequency range, said authentication signals comprising, for each period, a fixed first signal f 1 i characteristic of said terminal, and a variable second signal f 2 i ; said terminal and said monitoring device each including means for interchanging a first common value K 1 in the form of frequencies prior to a call being set up, means for implementing a common algorithm for generating respective second frequency values f 2 i and f' 2 i at each period T and depending at least on the preceding second frequency value, respectively f 2 i-1 and f' 2 i-1 ; said terminal further including means for emitting said frequencies f 1 i and f 2 i at each period; and said monitoring device further including means for comparing each first frequency f 1 i with predetermined first frequency values, and for comparing each received second frequency f 2 i with the corresponding calculated second frequency f' 2 i , over a predetermined approximation range corresponding to line transmission, and means for inhibiting said call as a function of the results of said comparisons.

Claim 2

A system for authenticating a call by analog frequency signals lying in a first or data range of frequencies between a transmitter/receiver terminal and a communications line, the system being characterized in that it further includes a monitoring device connected in said line, and in that: said terminal includes means for generating authentication frequency signals in addition to said communications signals with a periodicity T while a call is in progress, said authentication signals having frequencies lying in a second frequency range, said authentication signals comprising, for each period, a fixed first signal f 1 i characteristic of said terminal, and a variable second signal f 2 i ; said terminal and said monitoring device each including means for interchanging a first common value K 1 in the form of frequencies prior to a call being set up, means for implementing a common algorithm for generating respective second frequency values f 2 i and f' 2 i at each period T and depending at least on the preceding second frequency value, respectively f 2 i-1 and f' 2 i-1 ; said terminal further including means for emitting said frequencies f 1 i and f 2 i at each period; and said monitoring device further including means for comparing each first frequency f 1 i with predetermined first frequency values, and for comparing each received second frequency f 2 i with the corresponding calculated second frequency f' 2 i , over a predetermined approximation range corresponding to line transmission, and means for inhibiting said call as a function of the results of said comparisons.