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Spread spectrum (SS) communication relies on the assumption that some secret is shared beforehand among communicating nodes to establish the spreading sequence for long-term wireless communication. Strasser et al. identified this as the circular dependency problem (CDP). This problem is exacerbated in large networks, where nodes join and leave the network frequently, and preconfiguration of secrets through physical contact is infeasible. In this work, we introduce an efficient and adversary-resilient secret sharing mechanism based on two novel paradigms (intractable forward decoding, efficient backward decoding) called Time Reversed Message Extraction and Key Scheduling (TREKS) that enables SS communication without preshared secrets. TREKS is four orders of magnitude faster than previous solutions to the CDP. Furthermore, our approach can be used to operate long-term SS communication without establishing any keys. The energy cost under TREKS is provably optimal with minimal storage overhead, and computation cost at most twice that of traditional SS. We evaluate TREKS through simulation and empirically using an experimental testbed consisting of USRP, GNU Radio, and GPU-equipped nodes. Using TREKS under a modest hardware setup, we can sustain a 1--Mbps long-term SS communication spread by a factor of 100 (i.e., 100 Megachips per second) over a 200-MHz bandwidth in real time.