#75

SolvedKey exposed

The private key to this puzzle is public and the balance has been swept. Everything below was re-derived with secp256k1 and confirmed to match the address — never take a copied value on trust.

Address

1J36UjUByGroXcCvmj13U6uwaVv9caEeAt

mempool.space

Key range (hex)

0x4000000000000000000 ~ 0x7ffffffffffffffffff

Interval size

2^74 = 1.9×10^22

Balance

0.00000000 BTC · 5 tx

snapshot from 2026-08-23

Public key (compressed)

03726b574f193e374686d8e12bc6e4142adeb06770e0a2856f5e4ad89f66044755

Exposed on 31 May 2019, when the creator withdrew 1,000 satoshis from this address. This is the value BSGS and Kangaroo take as input.

Private key (already public)

0000000000000000000000000000000000000000000004c5ce114686a1336e07

The balance is zero. This value is useful for verification and learning only — import it into a wallet and you will find nothing there.

Method of attack

Pollard's Kangaroo

work ≈ 1.4×10^11 (2^37)

Browser (JS, 1 thread)the search tool on this site88 days

CPU · keyhunt, 8 threads4.8 hours

CPU · keyhunt, 16 threads2.4 hours

GTX 106011 min

RTX 30703 min

RTX 30902 min

RTX 409055 sec

RTX 509034 sec

RTX 4090 × 105 sec

RTX 4090 × 100under a second

RTX 4090 × 1,000the scale of a large poolunder a second

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.

Doing it

How to actually run this puzzle

Recommended: Kangaroo (GPU)

The public key is known, so the discrete logarithm is solved directly. The work drops from 2^74 to around 2^37.

0. Build (Linux · CUDA)

git clone https://github.com/JeanLucPons/Kangaroo
cd Kangaroo
make gpu=1 ccap=86   # ccap is your GPU's compute capability (4090=89, 3090=86, 1060=61)
# On Windows open VC_CUDA102/Kangaroo.sln in Visual Studio. macOS and AMD are not supported.

1. Input file — three lines: range start, range end, public key

cat > in75.txt <<'EOF'
4000000000000000000
7FFFFFFFFFFFFFFFFFF
03726B574F193E374686D8E12BC6E4142ADEB06770E0A2856F5E4AD89F66044755
EOF

2. Run

./kangaroo -t 8 -gpu -gpuId 0 -w save75.work -wi 300 -o found-75.txt in75.txt

Watch out for

Order matters in the input file — range start, range end, public key. Get it wrong and it finds nothing.
-d is the distinguished-point bit count. Leave it out and it picks one; only touch it when distributing.
-w and -wi save progress every five minutes. On a job that runs for days this is not optional.
To combine machines use -s (server) / -c (client) mode. It is more efficient than splitting the range.

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.

BitCrackGPU

Address brute force. The de facto standard for puzzles with no public key, and the only one that runs on AMD.

BitCracknot usable

The public key is known, so brute-forcing addresses is a waste. Kangaroo needs 2^37 operations where BitCrack runs 2^74.

A reality check

This one is already solved. The commands above are for learning — knowing the answer makes it a good way to confirm your tool actually works.

Build it with your own options Start from installation

#74

unsolved · 7.4 BTC · half the difficulty

#76

unsolved · 7.6 BTC · twice the difficulty