idea decades old so what's new what happened with Bitcoin well a downside the all of these systems have is that you need to know exactly who is participating in the protocol so the way that these systems work is as the protocol works based on identity so you have to know who is involved you need to know everybody in the system you know everybody in the system you can tell you know as who's sending you messages and who's not sending you messages and you can make decisions about what everybody else thinks the globally ordered log looks like the thing that these protocols did not tolerate was when you don't know everybody in the system and the problem when you don't know everybody in the system and you're not doing participation based on identity is that an attacker could create a whole bunch of identities there's nothing preventing an attacker from creating identities and remember we want a permissionless decentralized system we don't want to have some gatekeeper saying who can enter into and out of the system and given that we don't want to have that gatekeeper we can't just let people join willy-nilly and manufacture their own identities because if they do all of these protocols all of a sudden no longer work this is what's known as a Sybil attack okay when an attacker can create identities essentially for free and can swarm the good guys and take over the protocol so we're I'm gonna leave you is with this problem which is we want to figure out how to address the Sybil attack problem when creating a globally ordered log and and one way of doing that is to think about making identities costly so good guys can create new identities and can join the system and can execute the protocol bad guys could potentially create identities and join the system and execute the protocol but because identities actually cost something there's a limit there's an inherent limit they don't come for free the bad guys can only create so many and that's where I want to end are there any questions about that as we transfer over to attach yeah this percentage to deal with the security consensus that's you have synchronicity not necessarily so that problem is unsolvable in the case where there it a totally asynchronous system but there's there's a lot of different ways to create a model where for example if you have random coins then it is solvable in an asynchronous system so this is something that you might have heard of something called the cap theorem this is sort of a predecessor to that which indicates that in a totally asynchronous system without random coins consensus is actually impossible but that's there's there's different ways to sort of get around that and oftentimes people assume that the system is semi synchronous
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