committee vote for both blocks Figure 8 shows how Algorands performance is

Committee vote for both blocks figure 8 shows how

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committee vote for both blocks. Figure 8 shows how Algorand’s performance is affected by the weighted fraction of malicious users. The results show that, at least empirically for this particular at- tack, Algorand is not significantly affected. 10.5 Timeout parameters The above results confirm that BA steps finish in well un- der λ step (20 seconds), that the difference between 25th and 75th percentiles of BA completion times is under λ stepvar (5 seconds), and that blocks are gossiped within λ block (1 minute). We separately measure the time taken to propa- gate a block proposer’s priority and proof; it is consistently around 1 second, well under λ priority (5 seconds), confirming the measurements by Decker and Wattenhofer [18]. 11 FUTURE WORK This paper focused on the consensus mechanism for commit- ting transactions, and addressing the associated scalability and security challenges. There remain a number of open problems in designing permissionless cryptocurrencies: Incentives. In order to encourage Algorand users to par- ticipate, i.e., be online when selected and pay the network cost of operating Algorand, the system may need to include incentives, possibly in form of a reward mechanism. Design- ing and analyzing an incentive mechanism includes many challenges, such as ensuring that users do not have perverse incentives (e.g., to withhold votes), and that malicious users cannot “game the system” to obtain more rewards than users who follow the protocol (e.g., by influencing seed selection). Cost of joining. To join Algorand, new users fetch all ex- isting blocks with their accompanying certificates, which can comprise a large amount of data. Other cryptocurrencies face a similar problem, but since the throughput of Algorand is relatively high, this may create a scalability challenge. Forward security. Attackers may attempt to corrupt users over time, since identities of committee members are re- vealed after they send a message. If an attacker manages to obtain enough user keys, he could construct a fake certificate to create a fork. One solution would be for users to forget the signing key before sending out a signed message (and commit to a series of signing keys ahead of time, perhaps using identity-based encryption [11, 20]). 12 CONCLUSION Algorand is a new cryptocurrency that confirms transactions on the order of a minute with a negligible probability of fork- ing. Algorand’s design is based on a cryptographic sortition mechanism combined with the BA Byzantine agreement protocol. Algorand avoids targeted attacks at chosen partic- ipants using participant replacement at every step. Exper- imental results with a prototype of Algorand demonstrate that it achieves sub-minute latency and 125 × the throughput of Bitcoin, and scales well to 500,000 users.
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  • Spring '19
  • NA
  • hash function, Cryptographic hash function, Algorand

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