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Jörg F. Wittenberger [LibreList] Re: [redecentralize] Thoughts on decentralization and deperimeterization 2014-09-04 15:45:37 (5 years 5 mons 20 days 22:01:00 ago)
Am 03.09.2014 01:25, schrieb Paul Frazee:
> For some interesting reading, I'll refer you to Dominic's project, 
> https://github.com/dominictarr/secure-scuttlebutt.
>
>

Got one question here: this seems to replicate data.  Does it protect 
against malicious updates too?

To illustrate: I'm currently working on some simple payment system. (I 
picked "payment system" because that's something everyone understands 
without explanation of the app's purpose; however it's only an 
application which requires the features to be demonstrated.)

It works like this:

* Every "wallet" is a (sqlite) database holding a balance table of two 
columns: amount and currency. (Together with some user interface.)
* Users can create orders (documents) to transfer some amount to some 
other wallet. The receiver can either accept or reject.

(There is more, like maintaining nick names for wallets.  But those are 
irrelevant at this point.)

The important point: the wallet must make sure that it no order exceeds 
the senders balance and no receiver can accept the same order twice.  
(The total the currency must not change.)

Having a eventually consistent database is not enough here: we can't 
trust the peer to store a correct value.

Our solution is rather simple.  Each wallet is replicated (tolerating 
byzantine faults) at several notaries.

For a small world (like 5-20 peers) this could be *all* peers, to 
simplify the situation for the time being.  Now members of the group can 
readily use it.  Any attempt to cheat does not work.

However: This can not transfer money beyond the boundaries of the 
group.  (An incoming order would be signed by many notaries.  To no 
effect: the group would only trust those notaries in the receivers set 
and reject the order if the intersection of senders and receivers 
notaries is too small.)

For a larger world byzantine replication does not work, because it comes 
at quadratic communication cost.  Instead we would create "virtual 
banks": groups of individuals each running a peer and *contracted* (as 
in "having signed a legal contract") to keep it mostly online and 
prevent fraud.  Such a group could be used as an intermediary between 
wallets running at too disjoint groups.


So if I wanted to build applications like that one on scuttlebutt... 
possible?  How would I make sure the wallet is always correct?


Best

/Jörg
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