Friday, April 28, 2017

Ants Don't Have Blood

Ants have something called "hemolymph" which is a clear fluid that flows without the assistance of a circulatory system, but that's probably the least derpy thing to come out of the latest chapter in the anti-Jihan drama war.

There is no blood here..

Now, I love me some good bug hype as much as anyone, so when came online a couple days ago, I took notice.  Especially since I've got some ANTMINER S9s sitting in my garage that may be vulnerable to the issue.  Unfortunately, the number of red pixels on that website isn't really justified for this class of bug.  First off, the "bleed" suffix, referencing the old Heartbleed bug, has been reserved since then for memory disclosures.  This means vulnerable systems that you can hit in a funny way, and they disclose important information to you.  Most recently these are bugs like SSHBleed, or CloudBleed, etc.  There's no blood here though, both metaphorically in terms of urgency, and literally in terms of memory disclosure.  These miners have a feature built in that checks a web service to see if they are stolen, and if they are, they refuse to mine.  That's it.

Anti-Theft Telemetry

So what is Anti-Theft Telemetry?  This is a technology built into most phones, many new cars, and all sorts of embedded electronic gadgets that phone home regularly to determine if they are stolen, and if they are, the devices can be disabled.  If a mining rig gets stolen, the owner can report the theft to BITMAIN, and they can flip a switch, and your average thief will have a hard time getting the device working for them.
Now, I'll be the first to say that telemetry technologies are stupid, and in many ways, invasive, but it's also an extremely common, and often requested, theft deterrence feature.

Central Control

The thing that a lot of people have been freaking out over is the idea that Jihan, owner of BITMAIN, could shut down a huge part of the Bitcoin mining network if he wanted to, since a large portion of it is running on BITMAIN hardware.  While it is true that yes, he could screw over all his customers if he wanted to, it would damage his company irreparably, and for what?  A vast majority of the affected customers would be back online within a couple hours.  This, however, is no different than a large mining pool deciding to divert hashing power, or block users, except a mining pool could then steal its customers bitcoins as well.

The Man in the Middle

What I think is a much more serious concern is the Man in the Middle problem.  A malicious actor (and we've seen quite a few recently) could hijack the telemetry service and use it to make a political statement.  The derp-de-doo who implemented this feature didn't use HTTPS for the telemetry connection, which opens it up several points of attack.  Still though, the worst case scenario is denial of service, and since no one uses TLS for their mining traffic either, these points of attack are exactly the same as those that would hijack mining traffic itself, like the attacks we saw in 2014 that are still just as possible today.  Again, these attacks would net actual bitcoins, and are therefore much more likely for a profit driven attacker to go after.  The only threat (and it is a serious one) would be from those who would want to hurt BITMAIN's reputation.

Who done it?

One question that I feel isn't getting asked enough is, who did this?  We all know that Codenomicon found Heartbleed, Qualys found SshBleed, and Tavis found CloudBleed, but the AntBleed website has a distinct lack of identifying markers.

Besides there being nothing on the actual site, a quick whois will tell you that the site was registered with Namecheap, a registrar that allows you to register domains with Bitcoin.  It's also WhoisGuard protected, so whoever registered the domain didn't want anyone to know who they are.  The site is also being hosted on GitHub under an anonymous "antbleed" account which was used exclusively for setting up this site.  Luckily someone cloned the repo before the antbleed user deleted all their history, or we wouldn't even have that.

Clearly, whoever is promoting AntBleed doesn't want to be identified, which solidifies the suspicions that this was less of a bug report, and more of a pure political hit piece.  Jihan, owner of BITMAIN, upset a lot of people a couple months ago when he started speaking out against how the core Bitcoin developers were behaving, and began pointing the hashing power of his mining pool towards an alternative implementation, undermining the current core development team.  The retaliation has been swift, and strong, and most of all, shocking.

Wednesday, April 12, 2017

MyriadCoin : The Untold Story of the Invincible Blockchain

One of my favorite security mechanisms built into a cryptocurrency is the concept of the Multi-Algorithm PoW.  This means separate, floating difficulties that automatically adjust to ensure that miners on all algorithms get paid out equally.

The first coin I ever saw do this was RuCoin, released back in 2011, which worked with sha256 and scrypt.  I first heard about it in 2013 at the Bitcoin conference in San Jose.  ASIC miners for Bitcoin were finally starting to ship, and there was quite a bit of discussion around whether or not Bitcoin should switch up its Proof of Work algorithm, and exactly how it should do that.  As a huge proponent of trust agility, this idea that a cryptocoin could have two PoW algorithms with independently floating difficulties really blew my mind.  To extend on that, I really liked the idea of pluggable PoW algorithms that could be added and removed from a blockchain as needed, and could be reincentivized on a schedule.

Enter the Myriad

For some reason, RuCoin never released source, and eventually RuCoin died, but in early 2014, the hero of our story arrived, and it was called MyriadCoin.

Myriad was really interesting to me because it didn't just have two PoW algorithms, it had *five*, all floating independently.  To understand why this is a massive security advancement, you first need to understand how 51% attacks are executed.

How to perform an effective 51% attack:

ASIC Coin: One of the key threat actors in this scenario is a nation state able to manufacture custom ASICs to attack a network.  Algorithms that are ASIC friendly are, by design, extremely cheap to implement in hardware.  This also means that the security of the network is 100% dependent on the production lines of ASIC manufacturers who may or may not be open to the public about their product.

GPU Coin: These coins have algorithms that are a bit more expensive to implement in hardware.  The cheapest way for an attacker to attack a GPU Coin would likely be to spin up the required number of GPUs in Amazon's EC2 environment for just long enough to perform a double spend.

CPU Coin:  These coins bring crypto currencies back to their roots, as the most efficient way to mine these coins is on a CPU.  Usually this means that they require significant amounts of memory, or memory bandwidth, that isn't generally available on GPUs.  Unfortunately, what this means is that an attacker with a large botnet would not have a lot of trouble dominating the network for short periods of time, since they often can control 10s of millions of CPUs at any given time.

How MyriadCoin defends against 51% attacks:

Here's where the magic happens.  MyriadCoin has five different proof of work algorithms that all adjust difficulty dynamically.  Two of them ASIC algorithms, two of them GPU algorithms, and one of them a CPU algorithm.

sha256/scrypt: First up, sha256 and scrypt, our favorite PoW algorithms from Bitcoin and Litecoin.  MyriadCoin can also be merge mined with Bitcoin and Litecoin, so you can use your ASICs to mine Bitcoin and Litecoin, and also get some extra MYR on the side for free.

groestl/skein: Groestl and Skein were actually both SHA3 finalists, and the SHA-3 competition required that the algorithms could be cheaply implemented in hardware.  This means that they could be mined with FPGAs, or even ASICs some day, but they are currently being mined with GPUs.

yescrypt: I take some personal pride in this one.  YesCrypt is a CPU centric hashing algorithm created by SolarDesigner, infosec legend and creator of the John The Ripper password cracking toolset.  It was created for the Password Hashing Competition and was a finalist.  It was heavily inspired by scrypt, with a lot of extra defenses against TMTO attacks.  When MyriadCoin launched, an algorithm called Qubit was sitting in this spot, but I pushed for yescrypt pretty heavily on IRC and Reddit for a long time, and it finally got included.

The important part of this is that for any feasible 51% attack, an attacker would need to pin down at least three of the five algorithms, and very few attackers are capable of such feats.  Nation states who might be able to attack ASIC algorithms, and corporations who might be able to attack GPU algorithms, typically don't have the ability to operate large botnets, and those with the ability to operate large botnets generally don't have the physical presence required to operate large GPU or ASIC mines.  Furthermore, for any attack of extended duration, any algorithms that are getting pinned down would be deprioritized during the regular difficulty adjustments, so even pinning down three algorithms would not work for long.

The Tragedy of Vertcoin

A interesting case study in this area is that of Vertcoin.  It has had not one, but two major PoW changes in its history.  The first to run from ASIC mining, and the second to curb the threat of botnet takeovers.  Vertcoin was marketed, from the beginning, as the GPU forever coin.  It launched with a modified version of the scrypt algorithm that used an N-value of 11 rather than the N-value of 10, used by Litecoin, Doge, etc.  They also had the ability to easily bump to higher N values as needed for some extra memory requirements to presumably avoid the impending ASIC apocalypse that Litecoin and family were facing.

Unfortunately, in a move that no one expected, when KnC released their Titan ASIC miner for Litecoin, they included with it hardware support for a TMTO attack (mentioned earlier when discussing yescrypt) that effectively made the Titan miner work on Scrypt coins of any N value, notably targeting Vertcoin.

At that point, Vertcoin had no choice but to fork, and switch to a Password Hashing Competition finalist, Lyra2.  This worked well, but this wasn't the end of their problems.  Lyra2 was designed to be run on CPUs, so it became so popular on Botnets that they needed to fork once again in 2015 after it became clear that a single botnet was controlling more than 50% of the mining power.

Lessons for Bitcoin

With all this AsicBoost drama, and renewed talk of PoW switching, I still think that if this ever were to happen on the Bitcoin blockchain, there would need to be a gradual transition.  Maybe at first 99% of the mining rewards would still go to the SHA256 miners, and 1% would go to MAGICHASH, the magical perfect PoW algorithm that everyone wants to switch to.  The cut received by MAGICHASH could be gradually increased, and after a year it could be 50/50 rewards, and after two years, SHA256 could be phased out completely.  Of course, if the Bitcoin community can't even agree how to scale block size, it's hard to imagine that they'll be modifying their PoW algorithm any time soon.