Abstract: A system for generating a cryptokey (k) to be shared among entities (A, B) engaged in communications, in particular one known as the key predistribution system. Indentifiers (y.sub.A, y.sub.S) for the entities engaging in communications under a center and a center algorithm (G) which only the center knows are generated, then secret algorithms (x.sub.A, X.sub.B) distinct to each entity are generated on added to IC cards or other cipher generation means (2, 3). A cipher generation means (2, 3) is provided for each entity. The identifiers (y.sub.B, y.sub.A) of the other entity are applied to compute a cryptokey, whereby a common cryptokey is generated.Also disclosed is a system for communications using the above shared cryptokey.