Abstract: A method of establishing secure communication between users by means of a public key encryption/decryption system comprises the following steps: a center generates a pair of keys comprising a secret key and a public key, the center's public key is supplied to a user, this user generates a pair of keys specific to this user comprising a secret key and a public key but the public key of this user is encrypted with the center's public key, this user transmits to the center their own public key encrypted with the public key of the center, and the center decrypts the public key of this user and if this user is approved by the center, the center retransmits to this user the public key of this user encrypted with itself. This method provides centralized control of users' public keys.

Abstract: A flat multi-strand superconducting conductor with a separator.The conductor is constituted by transposed strands which form two layers (12, 14) on either side of an insulating separator (2, 3, 4) which is formed around a core (3, 4) including a continuous metal detector line so as to allow the transitions of the superconducting strands to be detected by measuring the voltage at the terminals of the conductor and compensating the induced voltage detected at the terminals of this detector line.Application to cryoalternators.