Quote from: gmaxwell on December 07, 2014, 06:20:28 AM

In this old thread I described how the Ripple consensus model was unsound... that it could be expected to spontaneously break unless the topology met certain characteristics which were unlikely to be met by any graph except a centrally controlled one and that without additional unspecified functionality (perhaps hidden in assumed behaviour of users or via centralization) couldn't resist sibyl attacks. Unfortunately Ripple's creators responded to these concerns-- to the extent that they responded at all-- with evasion and a seeming refusal to make a clear statement of their security assumptions that, coupled with their design, supported their security claims. And the media and finance industry seems to have largely swallowed their claims without much critical thinking seemingly counting on an orgy of social proof that seems to have been ultimately backed by the same nothingness that backs their pre-mined currency.

I wasn't the only person to point out these issues, more recently Ripple labs published a paper claiming the soundness of their model, which made a number of clearly illogical arguments and rested on many unclear and unsubstantiated assumptions, and it was also criticized by Andrew Miller, for many of the same reasons I criticized it here.

(and in this thread I was handicapped by the fact that ripple was closed source at this time: but even so its limitations were apparent simply from the seemingly impossible claims that its creators couldn't back up)

On Tuesday at a Bitcoin event I was still being harangued by Ripple/Stellar advocates claiming the absolute soundness of the system. I care about the whole cryptocurrency ecosystem since, in the minds of the public any failure is harmful to all of us, and I don't want to see anyone suffer losses not even the gullible... But it makes no sense for me to spend my limited time providing free consulting for the impossibly torrent of ill-advised, impossibility claiming, systems... especially when they're not thankful and/or respond with obfuscation that makes their work unrealizable or hand-waving without admitting their new assumptions. I don't want to see anyone get hurt, but ... hey, I spoke up a bit and people continued on anyways without asking the kind of tough questions they should have been asking. I'm certainly not going to spend all me time correcting everyone who is wrong on the internet, especially when altcoin folks have been known to play pretty dirty toward their critics. No one should assume that other people are going to go out of their way to beg them to not use something broken.

So, when I found out that Stellar spontaneously split consensus state, apparently just as I described in this thread, without even an attacker (though any consensus split is easily exploited by attackers of opportunity once it exists)-- Well, the only thing that surprised me was the burst of honesty in admitting that the system was unsound, but I was also disappointed that the lack of frankness about how fundamental the limitations are in this space-- instead advocating the hope of magical fixes sure to be found by a respected authority, and I was also disappointed that no mention was given of that fact that other experienced people in this space had warned of precisely these issues, going back several years. I also was saddened to see that no one noticed the dissonance in the 'temporary' solution of converting to a centralized model: If a system can be converted by some loss correcting central bank into a centralized system ... can we really say it was ever decentralized in the first place?

Perhaps in the future more people will ask the hard questions and demand better answers? If so, it would be worth more time for experienced people to spend time reviewing other systems and we could all benefit. Otherwise, perhaps those who aren't interested in standing up to some of the rigor we'd normally expect from a cryptosystem will stop calling their broken altcoins "cryptocurrencies". Those of us who actually want to build sound systems don't want our work sullied by these predictable failures, and being able to say "I told you so" is no consolation.

https://ripple.com/why-the-stellar-forking-issue-does-not-affect-ripple/