Algorand can guarantee that the probability for forks is neg ligible Algorand

Algorand can guarantee that the probability for forks

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Algorand can guarantee that the probability for forks is neg- ligible. Algorand may be extended to “detect and punish” malicious users, but this is not required to prevent forks or double spending. Proof-of-stake avoids the computational overhead of proof-of-work and therefore allows reducing transaction con- firmation time. However, realizing proof-of-stake in practice is challenging [ 4 ]. Since no work is involved in generating blocks, a malicious leader can announce one block, and then present some other block to isolated users. Attackers may also split their credits among several “users”, who might get selected as leaders, to minimize the penalty when a bad leader is caught. Therefore some proof-of-stake cryptocur- rencies require a master key to periodically sign the correct branch of the ledger in order to mitigate forks [ 32 ]. This raises significant trust concerns regarding the currency, and has also caused accidental forks in the past [ 44 ]. Algorand answers this challenge by avoiding forks, even if the leader turns out to be malicious. Ouroboros [ 31 ] is a recent proposal for realizing proof-of- stake. For security, Ouroboros assumes that honest users can communicate within some bounded delay (i.e., a strongly synchronous network). Furthermore, it selects some users to participate in a joint-coin-flipping protocol and assumes that most of them are incorruptible by the adversary for a significant epoch (such as a day). In contrast Algorand assumes that the adversary may temporarily fully control the network and immediately corrupt users in targeted attacks. Trees and DAGs instead of chains. GHOST [ 48 ], SPEC- TRE [ 49 ], and Meshcash [ 5 ] are recent proposals for increas- ing Bitcoin’s throughput by replacing the underlying chain- structured ledger with a tree or directed acyclic graph (DAG) structures, and resolving conflicts in the forks of these data structures. These protocols rely on the Nakamoto consensus using proof-of-work. By carefully designing the selection rule between branches of the trees/DAGs, they are able to substantially increase the throughput. In contrast, Algorand is focused on eliminating forks; in future work, it may be interesting to explore whether tree or DAG structures can similarly increase Algorand’s throughput. 3 GOALS AND ASSUMPTIONS Algorand allows users to agree on an ordered log of transac- tions, and achieves two goals with respect to the log: Safety goal. With overwhelming probability, all users agree on the same transactions. More precisely, if one honest 3
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user accepts transaction A (i.e., it appears in the log), then any future transactions accepted by other honest users will appear in a log that already contains A . This holds even for isolated users that are disconnected from the network—e.g., by Eclipse attacks [29].
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  • Spring '19
  • NA
  • hash function, Cryptographic hash function, Algorand

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