A particular concern with Ripple is what would happen if Ripple validators failed not by crashing, but by getting compromised and acting maliciously (so-called Byzantine failure). The Ripple paper states in Section 3.2 that "it would take (4n + 1)/5 Byzantine failures for an incorrect transaction to be confirmed" (where all nodes are assumed to have identical UNLs and n is the size of that UNL). I believe this is an error, as with a quorum size of 80% of n, it is easy to construct a counter-example. Suppose nodes v_1 and v_10 are honest, while v_2, ..., v_9 maliciously deviate from the protocol. Now consider the two 80% sets (v_1, ..., v_8) and (v_3, ..., v_10). Those two sets overlap at only malicious nodes that could prevent v_1 and v_10 from hearing about each other's transactions.
The nice thing about SCP is that it is optimally safe (Theorem 13 in the paper). That doesn't mean it guarantees safety under all possible configurations (e.g., two disjoint sets of nodes that don't know about each other). But it means that in any configuration where there exists some protocol that could guarantee safety, SCP will guarantee safety as well. That includes Byzantine failure scenarios. So you could translate UNLs into quorum slices and substitute SCP for Ripple's consensus algorithm, and if RPCA was already guaranteed safe, then SCP will be, too. The converse is not guaranteed; you could choose a configuration that is safe under SCP and risks forking under RPCA.
This paragraph does not explain how they are different from Ripple's approach only that they are in fact different.
I think the last line sums it up: "SCP is the first Byzantine agreement protocol to give each participant maximum freedom in choosing which combinations of other participants to trust."
As opposed to Ripple, where the trust is heavily biased towards the starter membership list, making it more centralized than one would want.
It’s biased because of a technical issue (consensus must be reached). How does the Stellar protocol solve this technical issue?
To me, the statement says essentially "you can trust us more than Ripple" with no explanation as to why.
https://www.quora.com/Why-did-Jed-McCaleb-leave-Ripple-to-st...
https://www.reddit.com/r/Stellar/comments/7n8ntb/david_schwa...
> David I always enjoyed working with you and I thought we had a degree of respect for each other so I'm pretty disappointed in your tone here. I don't really want to get into a big back and forth about this but this just isn't correct. When I left ripple the board was 2 people; myself and Chris.
> I left because I made the mistake of bringing Chris on as CEO and it ended up being untenable to work with him for a variety of reasons.
> I feel like I've been extremely restrained in my criticism of ripple despite the frivolous lawsuits from you guys the constant attacks on my character and my family. I know you are actually a good person but I think you are in too deep to see how horrible Chris has acted toward me.
> Stellar hasn't abandoned the idea of distributing the lumens widely and the original facebook distribution was actually a success but the software/ecosystem wasn't ready for it at the time so we stopped it. We will do something similar in the future. I don't think any attempt at an internet level protocol like stellar or ripple can be widely adopted with a for profit company owning the majority of the tokens.
> Stellar has always been focused on cross border payments so the IBM announcement isn't a pivot by any means.
> Stellar and ripple are going after two completely different use cases as far as I can tell so I don't understand the continued hostility.
Secure Scuttlebutt is a database protocol for unforgeable append-only message feeds.
"Unforgeable" means that only the owner of a feed can update that feed, as enforced by digital signing (see Security properties). This property makes Secure Scuttlebutt useful for peer-to-peer applications. Secure Scuttlebutt also makes it easy to encrypt messages.
https://scuttlebot.io/more/protocols/secure-scuttlebutt.html
SSB is deliberately “against consensus”, which makes it useless as a trustless decision-making tool. So I take your point that this property of Stellar seems to make Stellar useless for its stated purpose. (I haven't read the paper, so I may be very wrong.)
No.
If you’re worried about it, read the linked paper. The mechanics (and assumptions) are covered in painstaking detail.
I bet there is already CS research theory ready to apply to this design. (Easier said than done and I am just guessing really).
> Generally, membership in Byzantine agreement systems is set by a central authority or closed negotiation. Prior attempts to decentralize admission have given up some of the benefits. One approach, taken by Ripple, is to publish a “starter” membership list that participants can edit for themselves, hoping people’s edits are either inconsequential or reproduced by an overwhelming fraction of participants. Unfortunately, because divergent lists invalidate safety guarantees [Schwartz et al. 2014], users are reluctant to edit the list in practice and a great deal of power ends up concentrated in the maintainer of the starter list. Another approach, taken by Tendermint [Kwon 2014], is to base membership on proof of stake. However, doing so once again ties trust to resource ownership. SCP is the first Byzantine agreement protocol to give each participant maximum freedom in choosing which combinations of other participants to trust.