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We consider a slotted communication system consisting of a source, a cache, auser and a timestomping adversary. The time horizon consists of total $T$ timeslots, such that the source transmits update packets to the user directly over$T_{1}$ time slots and to the cache over $T_{2}$ time slots. We consider$T_{1}\ll T_{2}$, $T_{1}+T_{2} < T$, such that the source transmits to the useronce between two consecutive cache updates. Update packets are marked withtimestamps corresponding to their generation times at the source. All nodeshave a buffer size of one and store the packet with the latest timestamp tominimize their age of information. In this setting, we consider the presence ofan oblivious adversary that fully controls the communication link between thecache and the user. The adversary manipulates the timestamps of outgoingpackets from the cache to the user, with the goal of bringing staleness at theuser node. At each time slot, the adversary can choose to either forward thecached packet to the user, after changing its timestamp to current time $t$,thereby rebranding an old packet as a fresh packet and misleading the user intoaccepting it, or stay idle. The user compares the timestamps of every receivedpacket with the latest packet in its possession to keep the fresher one anddiscard the staler packet. If the user receives update packets from both cacheand source in a time slot, then the packet from source prevails. The goal ofthe source is to design an algorithm to minimize the average age at the user,and the goal of the adversary is to increase the average age at the user. Weformulate this problem in an online learning setting and provide a fundamentallower bound on the competitive ratio for this problem. We further propose adeterministic algorithm with a provable guarantee on its competitive ratio.

Age-Based Cache Updating Under Timestomping