
Understanding the Stellar Consensus Protocol - synesso
https://medium.com/interstellar/understanding-the-stellar-consensus-protocol-423409aad32e
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1053r
The authors of this protocol made a valiant effort to defend against sybil
attacks by requiring intersecting quorums. However, it's not clear to me that
they succeeded. Specifically, I worry that they are depending on people
running nodes to vet other nodes in some out of band fashion. Clever and
patient sybil attackers could insert themselves into the network over weeks or
months, and then disrupt it while shorting it on exchanges, or by conducting
double spend attacks against exchanges.

As was shown in Bitshares, which relied on holders of BTS to vote on "good"
block producers, users can not be relied upon to make these judgements. They
will either vote at random, or vote based on trivial stats like uptime. The
holders of BTS ultimately paid the price when the creators of the coin forced
through a proposal to increase the supply cap and the price collapsed as a
result, but the creators have since moved on to other coins.

It seems to me that proof of work works, and proof of stake (as implemented in
Tezos) may work, although it's not been running successfully for very long.
I'm very suspicious of other consensus algorithms protecting billions of $s
worth of assets.

~~~
mazieres
The Sybil attack doesn't work against SCP because, unlike proof-of-stake, the
validators are not anonymous. E.g., are you using Stronghold dollars? Then put
their validators in all of your quorum slices and you will be guaranteed not
to be forked from them. Eventually, every exchange and issuer should designate
one or more validators. By including the validators of the institutions you
care about in your quorum slices, you know you will be able to redeem and
trade the tokens at those places.

Now what makes SCP different from traditional BFT replication is not just that
the quorums are defined in a decentralized way, but that they require a
transitive closure of dependencies. So if you depend on stronghold and
stronghold depends IBM and binance also depends on IBM, then even if you don't
think you care about binance, you will still remain in sync with them.

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agorabinary
Who cares? The vast majority of Stellar's currency XLM is owned by the
founders just like Ripple, and their efforts to distribute this currency to
the public are entirely disingenuous. For example, their 2017 airdrop
purported to distribute up to 16% of the initial XLM to Bitcoin holders, while
less than 10% of that amount was actually claimed (as to be expected when you
make people jump through hoops to claim something of dubious value).

The crypto space has an near-infinite supply of new coins and new whitepapers
to trap the naturally curious into a hopeless cycle.

~~~
DanielFlower
While temiri is right, I'd like to continue the discussion that you've started
by mentioning that their last airdrop, done in collaboration with
blockchain.com, was also a fiasco. A lot of people didn't even bother claiming
anymore, and many of those who tried (including me and a buddy that lives in
the same building), weren't able to claim because the process was littered
with bugs. Hopefully, a serious non-profit foundation will take over (fork)
the open source Stellar tech, create a good and fair initial distribution
mechanism, and then restart the cryptocurrency. It would probably need the
help of governments or big corporations like Facebook/Google in order to
insure a fair initial distribution.

~~~
oh_sigh
I encountered one of those bugs and was able to get 'my' coins after maybe 3
back and forths with a human support person. It wasn't too hard for what could
be a free $500.

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drexlspivey
Good discussion on an old thread between D.Mazieres (protocol author), Greg
Maxwell and Vitalik
[https://news.ycombinator.com/item?id=9342348](https://news.ycombinator.com/item?id=9342348)

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badrabbit
The one thing I am curious about is the idea of reputation establishment. Has
there been any attempt to reduce impact of a sybil attack by introducing
reputation metrics?

What if for example with SCP quorum slices form only between nodes of
agreeable reputation where reputation could either be transaction confirmation
history or transaction participation history or some combination of both.

I would argue,if some form f reputation metric was in play,a simple 51%
majority (for unfederated) would not mean much,especially if each node gets to
unilaterally decide reputation metrics it finds agreeable which will make it
hard for a sybil attacker to know how many nodes of what reputation it needa
to control to succeed.where a failed sybil attack could reduce or eliminate
reputation of the nodes it used.

The whole idea is so simple I feel a bit cluelees even asking about it,but
does anyone know if similar consensus systems have been explored?

~~~
mazieres
The thing is that reputation isn't formed in a vacuum. E.g., in the case of
Stellar's blockchain, you have companies issuing assets like digital dollars
or carbon credits or shares in commercial real estate ventures. The tokens
have value because people trust their counterparties. Even in the case of XLM,
Stellar's "native" cryptocurrency, ultimately people believe it has value
because they can trade it for other assets on Stellar's built-in DEX or sell
it for fiat currency or other crypto at exchanges. It doesn't matter how many
Sybil nodes an attacker creates, if I place Kraken and Coinbase in my quorum
slice, I will remain in sync with their validators and know that I can
subsequently choose to deposit all of my tokens on those exchanges for
trading.

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jimmcslim
I'm reading Charlie Stross's (cstross here) "Neptune's Brood" at the moment,
which envisions an interstellar society constrained by physics (i.e. no
FTL)... I can imagine the SCP would play a role in such a society perhaps!

~~~
DennisP
I don't think it'll spoil anything to say Stross actually invented his own
digital currency protocol for that book, taking advantage of the speed of
light limit.

