KEY SHARING DEVICE AND SYSTEM FOR CONFIGURATION THEREOF

A method of configuring a network device for key sharing and a method for a first network device to determine a shared key are provided. The method of configuring uses a private modulus (p1) a public modulus (N), and a bivariate polynomial (f1) having integer coefficients, the binary representation of the public modulus and the binary representation of the private modulus are the same in at least key length (b) consecutive bits. Local key material for a network device is generated by substituting an identity number into the bivariate polynomial and reducing modulo the private modulus the result of the substitution to obtain a univariate polynomial. Security may be increased by adding (440) one or more obfuscating numbers to coefficients of the univariate polynomial to obtain an obfuscated univariate polynomial. In a use phase, the network device determines a shared cryptographic key, by substituting (530) the identity number of another network device into the univariate polynomial and reducing modulo the public modulus and reducing modulo a key modulus.