#82

Unsolved8.2 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 2⁸¹ keys in the interval, so sweeping all of it costs that many attempts (on average, half).

Address

13zYrYhhJxp6Ui1VV7pqa5WDhNWM45ARAC

mempool.space

Key range (hex)

0x200000000000000000000 ~ 0x3ffffffffffffffffffff

Interval size

2^81 = 2.4×10^24

Balance

8.20000000 BTC · 3 tx

snapshot from 2026-08-23

Method of attack

Address brute force

work ≈ 2.4×10^24 (2^81)

Browser (JS, 1 thread)the search tool on this site4.3×10^12 years — 308× the age of the universe

CPU · keyhunt, 8 threads9.6×10^9 years

CPU · keyhunt, 16 threads4.8×10^9 years

GTX 10603.8×10^8 years

RTX 307095,771,369 years

RTX 309051,078,063 years

RTX 409030,646,838 years

RTX 509019,154,274 years

RTX 4090 × 103,064,684 years

RTX 4090 × 100306,468 years

RTX 4090 × 1,000the scale of a large pool30,647 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 200000000000000000000:3ffffffffffffffffffff --continue progress-82.txt -o found-82.txt 13zYrYhhJxp6Ui1VV7pqa5WDhNWM45ARAC

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 200000000000000000000 ~ 3ffffffffffffffffffff.

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 30,646,838 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

#81

unsolved · 8.1 BTC · half the difficulty

#83

unsolved · 8.3 BTC · twice the difficulty