delvingbitcoin
Zawy’s Alternating Timestamp Attack
Posted on: August 13, 2024 18:48 UTC
Exploring the concept of exploiting blockchain difficulty adjustments, a unique strategy emerges when examining limitations less than a certain threshold, specifically if this limit were set to a 2x or even 2.5x maximum upward difficulty adjustment.
This approach involves manipulating the mining process through strategic timing to exploit the blockchain's difficulty adjustment mechanism effectively. Initially, the mining operation commences with a period that takes approximately (\sqrt{2}) times two weeks, followed by a second identical period. The third phase accelerates, taking the minimum legal time, which is calculated based on the blockchain's predefined interval, leading to an operation duration of roughly (2\sqrt{2} + \epsilon), equating to approximately 2.83 windows' worth of time. Remarkably, this sequence generates an output equivalent to 333 windows' worth of blocks without increasing the difficulty beyond its starting point.
Delving deeper into the mechanics, the attacker, possessing 100% of the hashrate, embarks on mining the first difficulty period over two weeks, intentionally post-dating it to (2×\sqrt{2}) weeks. This action adjusts the new difficulty to a level of (d_2 = \frac{1}{\sqrt{2}}×d_1). Proceeding to the next phase, the miner spends (\sqrt{2}) weeks on the difficulty period, post-dating yet again to (4×\sqrt{2}) weeks, which sets the subsequent difficulty to (d_3 = \frac{1}{\sqrt{2}}×d_2 = \frac{d_1}{2}). In the final stretch, a week is dedicated to mining the third difficulty period with minimal timestamp increase, resulting in a difficulty spike to (d_4 = 2×d_3 = d_1). This meticulous timing culminates in a total elapsed time of approximately 4.41 weeks, successfully mining three difficulty periods of blocks and resetting the difficulty to its original state. However, due to the strategic manipulation of timestamps, which have been extended to approximately 5.66 weeks, the system encounters a temporal discrepancy, preventing the broadcast of mined blocks, thus highlighting a potential exploit within the blockchain's difficulty adjustment protocol.