Monero a private, decentralized cryptocurrency has long been valued for its privacy features and ASIC-resistant mining algorithm, RandomX. But like any Proof of Work cryptocurrency, it faces the theoretical threat of a 51% attack. Let's examine what it would take for an attacker to pull this off in 2025.
What We're Working With
As of block 3,410,966 (May 13, 2025), Monero's network hashrate sits at 4.82 GH/s. To execute a 51% attack, an attacker needs to control at least 51% of this hashrate, which means they'd need approximately 2.46 GH/s of mining power.
The Hardware Options
XMRig RandomX Benchmark results
Price was taken from eBay for CPUs alone - examining the best-case scenario for CPU mining costs.
XMRig RandomX Benchmark Multi threaded results for CPUs with more than 15 samples.
| CPU | Hashrate (KH/s) | Samples | Price ($) | Price per KH/s ($/KH/s) | |
|---|---|---|---|---|---|
| 1. | AMD EPYC 9654 96-Core Processor | 184.82 | 189 | $1,994 | $10.79 |
| 2. | AMD EPYC 9B14 96-Core Processor | 177.28 | 19 | $1,999 | $11.27 |
| 3. | AMD EPYC 9754 128-Core Processor | 139.79 | 28 | $1,699 | $12.15 |
| 4. | AMD EPYC 9554 64-Core Processor | 137.76 | 16 | $2,034 | $14.76 |
| 5. | AMD Ryzen Threadripper PRO 7995WX 96-Cores | 109.65 | 18 | $10,888 | $99.30 |
| 6. | AMD Ryzen Threadripper PRO 3995WX 64-Cores | 105.82 | 89 | $1,645 | $15.55 |
| 7. | AMD EPYC 7T83 64-Core Processor | 103.71 | 35 | $1,218 | $11.75 |
| 8. | AMD EPYC 7763 64-Core Processor | 101.45 | 165 | $700 | $6.90 |
| 9. | AMD EPYC 7J13 64-Core Processor | 99.34 | 24 | $1,350 | $13.59 |
| 10. | AMD EPYC 7B12 64-Core Processor | 98.24 | 162 | $528 | $5.38 |
| 11. | AMD EPYC 7742 64-Core Processor | 98.16 | 237 | $739 | $7.53 |
| 12. | AMD EPYC 7B13 64-Core Processor | 98.00 | 43 | $819 | $8.36 |
| 13. | AMD EPYC 7H12 64-Core Processor | 96.97 | 77 | $774 | $7.98 |
| 14. | AMD EPYC 9V33X 96-Core Processor | 96.26 | 15 | $4,068 | $42.26 |
| 15. | AMD EPYC 7773X 64-Core Processor | 95.39 | 19 | $1,562 | $16.38 |
| 16. | AMD EPYC 7V12 64-Core Processor | 95.33 | 102 | $616 | $6.46 |
| 17. | AMD EPYC 7713 64-Core Processor | 93.71 | 114 | $678 | $7.24 |
| 18. | AMD EPYC 7662 64-Core Processor | 92.34 | 20 | $819 | $8.87 |
| 19. | AMD EPYC 7702 64-Core Processor | 88.20 | 139 | $600 | $6.80 |
| 20. | AMD Ryzen Threadripper 7980X 64-Cores | 84.03 | 17 | $4,474 | $53.24 |
Specialized Mining Hardware
The Antminer X5 by BITMAIN is a specialized mining device using RISC-V architecture CPUs:
- Hashrate: 212 KH/s
- Power consumption: 1350W (6.37 J/KH efficiency)
- Price: $1,100 per unit ($5.19 per KH/s)
It's important to note that this is not a traditional ASIC but rather a specialized device using high core count RISC-V processors optimized for Monero mining.
Best-Case Scenario Analysis
For this analysis, we'll focus solely on the hardware costs in a best-case scenario, ignoring the additional components needed for CPU mining to present the most favorable case.
CPU Option (AMD EPYC 7B12)
- Hashrate per unit: 98.24 KH/s
- Price per unit: $528
- Units needed for 51% attack: 25,043
- Total hardware cost (CPUs): $13.22 million
- Power consumption (at 225W per CPU): 5.63 megawatts
Specialized Hardware Option (Antminer X5)
- Hashrate per unit: 212 KH/s
- Price per unit: $1,100
- Units needed for 51% attack: 11,604
- Total hardware cost: $12.76 million
The Cloud Option
We chose Hetzner as the cloud provider of choice for this analysis due to their highly competitive pricing. Other cloud providers offer services at a higher cost.
Hetzner pricing
| Product | CPU | Hashrate (KH/s) | Monthly price ($) | Setup fee ($) | Price per KH/s ($/KH/s) |
|---|---|---|---|---|---|
| AX41-NVME | AMD Ryzen 5 3600 6-Core Processor | 8.84 | $42 | $0 | $4.75 |
| AX52 | AMD Ryzen 7 7700 8-Core Processor | 13.20 | $66 | $44 | $5.00 |
| AX102 | AMD Ryzen 9 7950X3D 16-Core Processor | 25.85 | $116 | $44 | $4.49 |
| AX162-R | AMD EPYC 9454P 48-Core Processor | 47.05 | $221 | $88 | $4.70 |
For a one-month attack (minimum server rental term) using Hetzner's dedicated servers, the costs would be:
- AX41-NVME: 278,192 servers needed × ($42 + $0) = $11.68 million
- AX52: 186,335 servers needed × ($66 + $44) = $20.50 million
- AX102: 95,180 servers needed × ($116 + $44) = $15.23 million
- AX162-R: 52,285 servers needed × ($221 + $88) = $16.16 million
Hardware Efficiency Comparison
Looking solely at the price per KH/s for hardware:
- AX102 (Cloud): $4.49 per KH/s
- AX41-NVME (Cloud): $4.75 per KH/s
- AX162-R (Cloud): $4.70 per KH/s
- AMD EPYC 7B12: $5.38 per KH/s
- Antminer X5: $5.19 per KH/s
- AMD EPYC 7V12: $6.46 per KH/s
- AMD EPYC 7702: $6.80 per KH/s
- AMD EPYC 7763: $6.90 per KH/s
- AMD EPYC 7742: $7.53 per KH/s
The cloud option using AX102 servers offers the best theoretical price-performance at $4.49 per KH/s, though practical limitations would make this approach impossible to implement at scale. Among the CPUs, the AMD EPYC 7B12 is now the most cost-effective at $5.38 per KH/s, slightly less efficient than the Antminer X5 specialized hardware.
Attack Economics
In our best-case scenario analysis:
For the AMD EPYC 7B12 approach:
- CPUs cost: $13.22 million
For the Antminer X5 approach:
- Hardware cost: $12.76 million
For the cloud approach (using AX41-NVME):
- First-month cost: $11.68 million
Conclusion
The cost analysis reveals several important insights about Monero's security against 51% attacks in 2025:
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Economic Barrier: The minimum cost of approximately $12.76 million (using Antminer X5 devices) represents a significant financial barrier for potential attackers. This is very close to the $13.22 million cost of using the most efficient CPUs (AMD EPYC 7B12). When additional costs such as facility rental, cooling infrastructure, power consumption, and operational staff are considered, the true cost would be substantially higher.
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Specialized Hardware Advantage: Despite RandomX being designed to favor general-purpose CPUs, specialized mining hardware like the Antminer X5 has emerged as the most cost-effective practical option. This demonstrates the ongoing challenge of maintaining ASIC resistance over time as manufacturers develop optimized solutions. However, the narrow margin between the Antminer X5 ($5.19 per KH/s) and the best CPU option (EPYC 7B12 at $5.38 per KH/s) suggests that RandomX has been relatively successful in preventing a dramatic efficiency gap.
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Cloud Limitations: While cloud options appear competitive on paper, they face practical limitations. No cloud provider would allow such a massive deployment for cryptocurrency mining, detection would lead to immediate termination, and the required scale (95,000+ servers for AX102) far exceeds available inventory. Due to inventory limitations, the attack would need to be carried out across several providers, complicating the orchestration and increasing the cost.
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Security Implications: The ~$12.8 million minimum attack cost must be weighed against the potential profit from such an attack. With Monero's market cap and daily transaction volume, the economic incentive for an attack remains limited, as the cost would likely exceed potential gains from double-spending.
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Future Considerations: As Monero's hash rate continues to grow with adoption, the cost of mounting a 51% attack will increase proportionally. However, ongoing developments in specialized mining hardware could potentially reduce the cost barrier over time.
Overall, Monero's RandomX algorithm continues to provide a reasonable level of security against 51% attacks, with the significant capital expenditure required serving as a powerful deterrent. The emergence of specialized hardware solutions like the Antminer X5 underscores the ongoing arms race between cryptocurrency designs and mining hardware optimization, though the relatively small efficiency advantage over CPUs suggests that RandomX remains effective at its core objective of ASIC resistance.