Systems and methods that allow the formation and distribution of session keys amongst a dynamic group of users communicating over an unreliable, or lossy, network. The systems and methods according to this invention allow an intermediate session key contained in an intermediate key distribution broadcast to be determined by receiving a preceding key distribution broadcast that precedes the intermediate key distribution broadcast, the preceding key distribution broadcast including a first portion of the intermediate session key; receiving a subsequent key distribution broadcast that follows the intermediate key distribution broadcast, the subsequent key distribution broadcast including a second portion of the intermediate session key that is distinct from the first portion; and combining at least the first portion of the intermediate session key contained within the preceding key distribution broadcast and the second portion of the intermediate session key contained within the subsequent key distribution broadcast to obtain the intermediate session key.