Byzantine Generals Problem


Bitcoin’s resolution to the double spending downside – distributing the ledger amongst

the 1000’s of nodes in a peer-to-peer community – presents one other downside. If

each node on the community has an entire copy of the ledger that they share with the

friends to which they join, how does a brand new node connecting to the community know

that she isn’t being given a falsified copy of the ledger? How does an current node

know that she isn’t getting falsified updates to the ledger? The troublesome job of

reaching consensus amongst distributed events who don’t belief one another is one other

longstanding downside within the laptop science literature often called the Byzantine

Generals Downside, which Bitcoin additionally elegantly solved.

The Byzantine Generals Downside posits that a variety of generals every have

their armies camped outdoors a metropolis that they’ve surrounded. The generals know

that their numbers are massive sufficient that if half their mixed pressure assaults on the

similar time they are going to take the town, but when they don’t assault on the similar time they are going to

be unfold too thinly and will likely be defeated. They will solely talk by way of

messenger, they usually haven’t any means of verifying the authenticity of the messages being

relayed. Additionally they suspect that among the generals of their ranks are traitors who

will ship pretend messages alongside to their friends. How can this huge group come to a

consensus on the time of assault with out using belief and with out a central

authority, particularly when there’ll possible be makes an attempt to confuse them with pretend


In essence, this is identical downside confronted by Bitcoin’s ‘miners’, the specialised

nodes that confirm new transactions and add them to the distributed ledger. Bitcoin’s

resolution is to require additions to the ledger to be accompanied by the answer to a

mathematical downside that may be very troublesome to unravel however easy to confirm. (That is

very like calculating prime components; expensive to do, however straightforward to test.) New

transactions are broadcast in a peer-to-peer style throughout the community by events to

these transactions. Miners have a look at these transactions and make sure by checking their

copy of the ledger (the block chain) that they aren’t double-spends.


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