A method for providing authentication of a user of a recipient unit when the recipient unit is off-line includes storing one or a plurality of one-time challenge-reply sets based on an on-line communication with a sender unit. In one example, each of the one-time challenge-reply sets includes at least a one-time challenge-reply pair for use in off-line authentication of the user for a particular resource available through the recipient unit. When the user is offline, the method includes selecting at least one of the plurality of stored one-time challenge-reply sets for off-line authentication of the user for the particular resource available through the recipient unit. The one-time challenge-reply sets may be associated with an article.