A method for producing a proof of the presence and/or of the availability of an entity in a site over a period that is greater than or equal to a presence threshold, the method including: successively transmitting messages, the messages being generated from a secret such that the secret may be reconstituted by having the knowledge of a given number of messages that is greater than or equal to a threshold, each message being transmitted over a transmission period whose duration is chosen such that the product of the duration of the transmission period times the threshold is substantially equal to the presence threshold; comparing the secret and a secret candidate generated from messages received by the entity; the proof being produced only if the secret and the secret candidate are equal.