A method for managing keys making it possible for a user to access one or more given services S in a communication system, the user who cannot be continuously connected to this service, comprising the generation of a key K(t) providing access to the service of day [t] for all the t<t fin, said method comprising at least the following steps: generating said key by using a one-way function f in the following manner: • using a root key K(t fin) and generating the key K(t fin -1) for the day [t fin -1] prior to the day t fin, by using the function f such that K(t fin -1) = f(K(t fin)), • using the new value of key K(t fin -1) in order to generate the key for the previous day K(t fin -2) and reiterating this step over the limited time period of day [t] to day [t+d] in order to obtain the chain K(t+d-1), K(t+d-2)... sending each day t, the key K(t+d) to the users or user group having a trust level d, and: toward the end of the period of validity of the current chain for the traffic key, for the receivers or users having a trust level d for a first period and a trust level d* for a second period storing two types of traffic keys: • A current traffic key K(t+d) allowing access for the last days under the control of the current chain K(), with the trust level d, • A second traffic key K*(t+d*) allowing access for the future days under the control of a new chain K*() with a trust level d* which may be different from the trust level d. generating said key by using a one-way function f in the following manner: • using a root key K(t fin) and generating the key K(t fin -1) for the day [t fin -1] prior to the day t fin, by using the function f such that K(t fin -1) = f(K(t fin)), • using the new value of key K(t fin -1) in order to generate the key for the previous day K(t fin -2) and reiterating this step over the limited time period of day [t] to day [t+d] in order to obtain the chain K(t+d-1), K(t+d-2)... • using a root key K(t fin) and generating the key K(t fin -1) for the day [t fin -1] prior to the day t fin, by using the function f such that K(t fin -1) = f(K(t fin)), • using the new value of key K(t fin -1) in order to generate the key for the previous day K(t fin -2) and reiterating this step over the limited time period of day [t] to day [t+d] in order to obtain the chain K(t+d-1), K(t+d-2)... sending each day t, the key K(t+d) to the users or user group having a trust level d, and: toward the end of the period of validity of the current chain for the traffic key, for the receivers or users having a trust level d for a first period and a trust level d* for a second period storing two types of traffic keys: • A current traffic key K(t+d) allowing access for the last days under the control of the current chain K(), with the trust level d, • A second traffic key K*(t+d*) allowing access for the future days under the control of a new chain K*() with a trust level d* which may be different from the trust level d. toward the end of the period of validity of the current chain for the traffic key, for the receivers or users having a trust level d for a first period and a trust level d* for a second period storing two types of traffic keys: • A current traffic key K(t+d) allowing access for the last days under the control of the current chain K(), with the trust level d, • A second traffic key K*(t+d*) allowing access for the future days under the control of a new chain K*() with a trust level d* which may be different from the trust level d. • A current traffic key K(t+d) allowing access for the last days under the control of the current chain K(), with the trust level d, • A second traffic key K*(t+d*) allowing access for the future days under the control of a new chain K*() with a trust level d* which may be different from the trust level d.