  With the increasing adoption of decentralized information systems based on a
variety of permissionless blockchain networks, the choice of consensus
mechanism is at the core of many controversial discussions. Ethereum's recent
transition from (PoW) to proof-of-stake (PoS)-based consensus has further
fueled the debate on which mechanism is more favorable. While the aspects of
energy consumption and degree of (de-)centralization are often emphasized in
the public discourse, seminal research has also shed light on the formal
security aspects of both approaches individually. However, related work has not
yet comprehensively structured the knowledge about the security properties of
PoW and PoS. Rather, it has focused on in-depth analyses of specific protocols
or high-level comparative reviews covering a broad range of consensus
mechanisms. To fill this gap and unravel the commonalities and discrepancies
between the formal security properties of PoW- and PoS-based consensus, we
conduct a systematic literature review over 26 research articles. Our findings
indicate that PoW-based consensus with the longest chain rule provides the
strongest formal security guarantees. Nonetheless, PoS can achieve similar
guarantees when addressing its more pronounced tradeoff between safety and
liveness through hybrid approaches.
