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of Consistent, available at http:// bit .ly/ 2XVRMuF; NULS (2019) Why it is Impossible to Solve Blockchain Trilemma?,
available at https:// bit .ly/ 2W7Dkzt; See also Kleppmann, M (2015) A Critique of the CAP Theorem, available at https://
bit .ly/ 2W2h0XN
277 Hence blockchain’s goals of striving to reach maximum levels of decentralization inherently result in a decrease in
scalability and/or security.
278 For discussions of these potential tradeoffs and concerns, see Kosba, A et al. (2016) Hawk: The Blockchain Model
of Cryptography and Privacy-Preserving Smart Contracts, available at http:// bit .ly/ 2xRBpVu; Greenspan, G (2016)
Blockchains vs Centralized Databases, available at https:// goo .gl/ gKfoym; and R3 (2016) Introducing R3 Corda™: A
Distributed Ledger Designed for Financial Services, available at https:// goo .gl/ IgD1uO; and Deloitte (2016) Blockchain:
Enigma. Paradox, Opportunity, available at https:// goo .gl/ yNjtFE; and Irrera, A (2016) Blockchain Users Cite
Confidentiality As Top Concern, available at https:// goo .gl/ IIuuua.
279 Society for Worldwide Interbank Financial Telecommunication (SWIFT) - supplies secure messaging services and
interface software to wholesale financial entities.
280 See further Greenspan, G (2016) Understanding Zero Knowledge Blockchains, available at https:// goo .gl/ r9P4jZ.
Greenspan is founder and CEO of Coin Sciences, a company developing the MultiChain platform for private blockchains.
281 In cryptography, a zero-knowledge proof or zero-knowledge protocol is a method by which one party (the prover)
can prove to another party (the verifier) that a given statement is true, without conveying any information apart from
the fact that the statement is indeed true. Quisquater, J-J, (2016) How to Explain Zero-Knowledge Protocols to Your
Children, available at http:// bit .ly/ 2Sm8l1P
282 Zcash payments are published on a public blockchain, but the sender, recipient, and amount of a transaction remain
private. Zcash uses different encryption approaches to keep both transactions and identities private. See http:// bit .ly/
2M116uY
283 Moos, M (2019) Largest Bitcoin Mining Pools Gutted as Bitmain Reels, available at http:// bit .ly/ 2XZ2q3R
284 The top four Bitcoin-mining operations had more than 53%of the system’s average mining capacity per week. By the
same measure, three Ethereum miners accounted for 61%.’Orcutt, M (2018) How secure is blockchain really?, available at
http:// bit .ly/ 2SoTOCI
285 Malicious miners who can control hashing power for POW consensus mechanisms could mine faster than competitors
and could create the longest chain in the network and overrule honest miners with a shorter chain, thus controlling
which transactions are added on the blockchain. See Nakamoto (2011); Nesbit, M (2018) Vertcoin (VTC) Was
Successfully 51% Attacked, available at https:// bit .ly/ 2Hpr09s
286 Nakamoto, S (2011) Bitcoin: A Peer to Peer Cash System, available at http:// bit .ly/ 32Bje4n
287 Nambiampurath, R (2019) Cryptocurrency Exchanges Are the Biggest Targets of 51% Attacks, available at http:// bit .ly/
2XWhP4T
288 Moos, M (2018) Explained: 51 Percent Attacks on Bitcoin and Other Crypto-currencies, available at http:// bit .ly/ 2XWip2z
289 Eyal I & Sirer E (2018) Majority Is Not Enough: Bitcoin Mining Is Vulnerable, available at http:// bit .ly/ 2JG7Xsp
290 Gola, Y (2018) Vertcoin Hit by 51% Attack, Allegedly Lost $100,000 in Double Spending, available at http:// bit .ly/
2SpcQsu; Nesbit, M (2018) Vertcoin (VTC) Was Successfully 51% Attacked, available at https:// bit .ly/ 2Hpr09s
291 Hertig, A (2018) Blockchain’s Once-Feared 51% Attack Is Now Becoming Regular, available at http:// bit .ly/ 2Ltb0WJ
292 Eyal I & Sirer E (2018) Majority Is Not Enough: Bitcoin Mining Is Vulnerable, available at http:// bit .ly/ 2JG7Xsp
293 Or even an innocent mining pool.
294 If there are such rewards.
295 By reusing a transaction input in Bitcoin.
296 The further back in the chain a block is, the more likely it is finalized and unlikely to be superseded by a longer chain.
297 Others have calculated the security level of 6 confirmation blocks has been calculated as 99.99% if the attacker
controls 8% of the hashing power. Grigorean, A (2018) Latency and Finality in \Different Crypto-currencies, available at
https:// bit ,J .ly/ 2VYNEts
298 Mosakheil, J (2018) Security Threats Classification, available at http:// bit .ly/ 2XPJXf8
299 The merchant should consider connecting to a sufficiently large number of random nodes on the network to limit
the chances of not seeing a double spend transaction. See Bamert, T & Decker, C et al. (2013) Have a Snack, Pay with
Bitcoins, available at https:// bit .ly/ 2WbT3h1

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