#84

Unsolved8.4 BTC

Still unsolved, and the public key is not known either — so the only approach is generating keys through the interval one at a time and comparing addresses. There are 2⁸³ keys in the interval, so sweeping all of it costs that many attempts (on average, half).

Address

1CMq3SvFcVEcpLMuuH8PUcNiqsK1oicG2D

mempool.space

Key range (hex)

0x800000000000000000000 ~ 0xfffffffffffffffffffff

Interval size

2^83 = 9.7×10^24

Balance

8.40001500 BTC · 4 tx

snapshot from 2026-08-23

Method of attack

Address brute force

work ≈ 9.7×10^24 (2^83)

Browser (JS, 1 thread)the search tool on this site1.7×10^13 years — 1,234× the age of the universe

CPU · keyhunt, 8 threads3.8×10^10 years — 2.8× the age of the universe

CPU · keyhunt, 16 threads1.9×10^10 years — 1.4× the age of the universe

GTX 10601.5×10^9 years

RTX 30703.8×10^8 years

RTX 30902.0×10^8 years

RTX 40901.2×10^8 years

RTX 509076,617,095 years

RTX 4090 × 1012,258,735 years

RTX 4090 × 1001,225,874 years

RTX 4090 × 1,000the scale of a large pool122,587 years

All approximate. Implementation, clocks and target count move these by multiples, so read the order of magnitude and nothing finer. The calculator lets you put your own rate in.

Finding it is not the same as keeping it

A transaction moving puzzle funds carries the public key and the signature. The moment it reaches the mempool, bots take the same coins with a higher fee. That is exactly how #66 and #69 were lost. How to prevent it

Doing it

How to actually run this puzzle

Recommended: BitCrack (GPU)

With no public key there is nothing to do but generate addresses one at a time and compare. BitCrack does that on the GPU. On NVIDIA that means the CUDA build, cuBitCrack.

0. Build (Linux · CUDA)

git clone https://github.com/brichard19/BitCrack
cd BitCrack
make BUILD_CUDA=1
# On Windows, open BitCrack.sln in Visual Studio and build the cuKeyFinder project
# to get cuBitCrack.exe. macOS is not supported.

Run

./cuBitCrack -d 0 -b 288 -t 256 -p 1024 -c --keyspace 800000000000000000000:fffffffffffffffffffff --continue progress-84.txt -o found-84.txt 1CMq3SvFcVEcpLMuuH8PUcNiqsK1oicG2D

Watch out for

The best values for -b/-t/-p differ per GPU. Run it once at the defaults, look at the rate, then adjust.
Always include --continue. It keeps your position across restarts.
To split across machines, turn on “split the work” above. --share divides the range without overlap.
This shard covers 800000000000000000000 ~ fffffffffffffffffffff.

Other options

keyhuntCPU

CPU only. Handles both addresses and public keys, and is the easiest to install — good for learning and for checking your setup.

Kangaroonot usable

This puzzle's public key is not exposed. There is no discrete logarithm to solve.

A reality check

On a single RTX 4090 this takes 1.2×10^8 years. That is not “eventually”; in most cases it means “no”. Doing it anyway means accumulating GPUs or joining a pool.

Build it with your own options Start from installation

#83

unsolved · 8.3 BTC · half the difficulty

#85

solved · twice the difficulty