Abstract: In one aspect, the present invention relates to a method of cryptographic processing of a message, the method comprising: —establishing communication between a first communication unit and a second communication unit in a communication domain comprising a communication channel; —defining, by the second communication unit, an integer a as a first private key and a number KA as a first public key, the first public key being a number determined based on a prime integer p, a generator prime integer g and the first private key; —making the first public key KA available to the first communication unit; —causing the first and the second communication units to share the prime number p and the generator number g; defining, by the first communication unit, an integer b as a second private key and a number KB as a second public key, the second public key being a number determined based on the prime number p, the generator number g and the second private key; —determining by the first communication unit an encryption exp