How much money would be required to cloud mine 51% of the network hash rate?

Question

Cloud mining is generally a very expensive way to mine over the long run.

However if the goal was to mine only for one day and in attempt to 51% attack a network it might be cheaper than purchasing equipment.

Approximately how much money would be needed to lease enough cloud mining hashing power to 51% the Monero network for one day?

Assume for calculation purposes the current hash rate wss 21.1 Mh/s before the cloud mining attack began. Also assume that is would take at least one day for the network to respond (and increase its mining efforts) to counter an attack.

Answer 1

Assuming a current hashrate of 21.1 MH/s, an attacker would need a bit more than 21.1 MH/s to perform a 51% attack. This assumes that doubling the hashrate for a day doesn't drive miners out. According to Fluffypony's slides¹ from his presentation to a group of bankers at the Thales User Group², the rental price of 1 KH/s is approximately 13.11$. Thus, an attacker would need to spend 13.11 * 22,000 (this gives you approximately 51%, i.e., 22/43.1 = 51.04%) = 288,420 $ per day to perform a 51% attack on Monero.

However, it should be noted that, in practice, less than 51% could be needed to perform an attack. If I recall correctly something like 35-40% is already sufficient, in case of lucky variance. This would bring the cost per day down to approximately 200,000 $ - 225,000 $ a day. However, to sustain his attack, an attacker would need to constantly have >50%, because variance reduces over time.

Sources:

[1] https://cloud.getmonero.org/index.php/s/gFLjnZ40Oo14kY5 - Slide 27

[2] https://twitter.com/fluffyponyza/status/760078858867671041

Answer 2

I think on AWS the most economical way to mine is with is a g2.2xlarge which costs $0.2017 per hour at spot price right now. I believe you can get on average around 1 kH/s with the GPU and CPU combined on one of these.

In order to 51% attack from scratch, one would need 21.1 Mh/s, or 21,100 instances. So, that would be $4,256/hr and $102,141/day.

Keep in mind these are back of the envelope calculations, and they're definitely not taking into account the fact that if someone launched that many instances they would probably drive the spot price up.

Answer 3

Over and above the AWS cluster pricing, and my rental calculations that were part of my Thales User Group presentation, I've struggled to find a reasonable way to calculate this. My most recent reasonable calculation is below.

Calculation Assumptions

Current BTC Price: $580 Nvidia GTX 970 Performance: 420 h/s Current Monero Hashrate: 19.97 Mh/s Days in a Month: 30.4375

Assumption Basis

Per this video, by IMineBlocks, he gets about 425h/s on an Nvidia GTX970 once its warmed up (towards the end of the video). Let's call it 420h/s to be conservative.

Most mining rig rental outfits don't support Monero's mining algorithm, but NiceHash have a generic rental option for their farm of GXT970s. They have 50 rigs, with 6 cards a rig, so it's a reasonably sized farm for rent.

They have various pricing levels, and their pricing is in Bitcoin. In addition, the Monero hashrate isn't static, so this exercise is pretty fluid. I've included as much of the raw numbers as possible so that this can be updated from time to time. Please note that numbers are rounded for convenience, but calculations used actual values up to 10 decimal places.

Rental Pricing Options

The pricing below is for a single rig, consisting of 6x GTX970s, which would run at around 2.5 kh/s.

• 3 month rent: 3.75 BTC ($2 175.00), which is $23.8193 per day
• 6 month rent: 5.625 BTC ($3 262.50), which is $17.8645 per day
• 12 month rent: 7.5 BTC ($4 350.00), which is $11.9097 per day

Thus, at each of those levels this is what it would cost -

• 3 month rental pricing: $9.4521 per-kh/s-per-day
• 6 month rental pricing: $7.089 per-kh/s-per-day
• 12 month rental pricing: $4.7260 per-kh/s-per-day

Final Calculation

Based on a 51% hashrate requirement, this is what it would cost you (assuming you were willing to commit to the various pricing levels, and there were enough rigs available at this price) -

• 3 month rental pricing: $96 290 per day ($8.792 million to sustain it over the 3 month period)
• 6 month rental pricing: $72 217 per day ($13.189 million to sustain it over the 6 month period)
• 12 month rental pricing: $48 145 per day ($17.585 million to sustain it over the 12 month period)