updating a bit more

Author: AnomalRoil

blog/2025-01-31-how-many-5090-to-break-sha1.md

@@ -83,12 +83,16 @@ $\frac{2^{63.4}\;\text{H}}{68.9\;\text{GH/s}} =  49034.2\;\text{hours}$
 
 using our brand new RTX 5090 GPU, which is roughly 5.6 GPU-years, also very far from the 107 GPU-year it took in 2020!
 
+## Make it happen in 2025
+
 But here’s a trick with these kind of attacks: they parallelize really well! So we could just use more GPUs, maybe 8, and then we could get a SHA-1 collision in only 74 days… Actually just using 2 RTX 5090s would allow us to find a collision in 296 days, which would still be in 2025!
 
 And that would come at a cost of ~\$3,998 for our 2 GPUs, plus 296 days of consuming 2 times 575 watts at a cost of \$0.18 per kWh (average cost in December 2024 in the USA), which is \$1,470 of electricity costs for running our GPUs until we find our collision. Therefore finding a SHA-1 collision “at home” in 2025 could cost us roughly \$5,468.
 
 But let’s be honest, no one builds a GPU farm just to find a SHA-1 collision when one can just rent some beefy GPU instances… And funnily the on-going AI hype has led to a significant increase in options in the landscape of GPU rentals. For example, an instance of 8 beefy RTX 4090 GPUs with a hash rate of ~408GH/s can be rented for as little as \$3 per hour and no more than \$5.5 per hour… Having found 22 such instances, I could find a collision in less than 5 days at a cost of less than \$12,000! So yeah, still a bit too long and too expensive for a CTF challenge! 
 
+## Can we be faster?
+
 Also note that this is not taking possible ASICs into account, unlike the 2021 paper "On The Cost of ASIC Hardware Crackers: A SHA-1 Case Study" which answers our question when assuming custom ASICs are an option:
 
 > In particular, we remark that the chosen-prefix collisions for SHA-1 can be generated in under a minute, with an ASIC cluster that costs a few dozen Millions dollars. Such ability would allow an attacker to apply the SLOTH attack on TLS or SSH connections using SHA-1.
@@ -100,6 +104,8 @@ With such power, you’d expect to find hundreds of collisions every second! But
 
 In a more realistic way, it would take less than a day to find a SHA-1 collision on a super-computer such as the one owned by the US Department of Energy's Oak Ridge National Laboratory (ORNL) named "Summit", and the fastest super-computer in the world, El Capitan, relies on a whopping 43,808 AMD MI300A GPUs, and each of these MI300A GPUs are able to pump at least 22GH/s (or $2^{34}$ H/s) SHA-1 computations (according to [some recent benchmarks](https://www.youtube.com/watch?v=D4aIl0tzILE)), meaning El Capitan can run $43808 \cdot 2^{34} \approx 2^{49}$ hashes per second on its GPUs, meaning it reaches the $2^{61.6}$ hashes required in roughly an hour! El Capitan however has an estimated cost of $600 million, so that might not be a cost-effective option…
 
+## Conclusion: finding a SHA-1 collision in 2025
+
 Finally, looking back at the prediction we quoted earlier, can we really find a SHA-1 chosen-prefix collision for less than \$10,000 in 2025? Well, not if we want it to finish in 2025 and assume an electricity price of \$0.18 per kWh, and also not using rented GPUs. But if we purchase just 2 RTX 5090s at \$1999 each (let’s assume you’re not getting the fancy, expensive versions), and have them running for the 413 days it would take them to find a SHA-1 **chosen-prefix collision** for roughly \$5065 of electricity cost, then we could find one for less than \$10,000!   
 
 Most remarkably, for the basic SHA-1 collision, we can see that in only 8 years, we're down from an attack costing ~110 GPU years to an attack costing ~8 GPU-years in 2020 (thanks to both theoretical improvements & newer GPUs) to less than 2 GPU years nowadays (thanks to newer, much faster GPUs). Funnily, this is roughly in line with what Moore’s law would have told us, who could have thought...

docs/dev-guide/04-HTTP_API.md

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