Patent ID: 8744079

Claim:
A computer-implemented method of rendering data transmitted via a communications system accessible solely to a predefined group of users of the communications system, comprising: a) making available solely to each user of said group i) a user secret s i , wherein s i equals f 1 (R, ui), and f 1 is a first one-way function operating on a root key R and a unique public identifier for that user (ui); and ii) a public identifier (uj) for each other user in said group; b) wherein a deriving user, employing a computer, i) derives a group key by operating a second one-way function (f 2 ) on parameters comprising: a) the deriving user's secret s i ; and b) the public identifier(s) for each of said one or more other user of said group (u 1 , u 2 , . . . u j−1 , u j+1 , . . . , un- 1 , u n ); f 2 being selected so that: f 2 ( f 1 ( R,u 1 ), u 2 , . . . ,u n )= f 2 ( f 1 ( R,u 2 ), u 1 ,u 3 ,u 4 . . . ,u n )= . . . = f 2 ( f 1 ( R,u n ), u 1 ,u 2 ,u 4 . . . ,u n −1); and ii) encrypts said data using the group key as input to an encryption algorithm; and c) transferring said encrypted data to each other user in said group via said communications system.