NEEDLESPACE
KREN
The 160/#51

#51

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

1NpnQyZ7x24ud82b7WiRNvPm6N8bqGQnaS

mempool.space
Key range (hex)

0x4000000000000 ~ 0x7ffffffffffff

Interval size

2^50 = 1.1×10^15

Balance

0.00000000 BTC · 3 tx

snapshot from 2026-08-23

Public key (compressed)

028c6c67bef9e9eebe6a513272e50c230f0f91ed560c37bc9b033241ff6c3be78f

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)

00000000000000000000000000000000000000000000000000075070a1a009d4

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 ≈ 3.4×10^7 (2^25)
Browser (JS, 1 thread)the search tool on this site31 min
CPU · keyhunt, 8 threads4 sec
CPU · keyhunt, 16 threads2 sec
GTX 1060under a second
RTX 3070under a second
RTX 3090under a second
RTX 4090under a second
RTX 5090under a second
RTX 4090 × 10under a second
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 2^50 to around 2^25.

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 > in51.txt <<'EOF'
4000000000000
7FFFFFFFFFFFF
028C6C67BEF9E9EEBE6A513272E50C230F0F91ED560C37BC9B033241FF6C3BE78F
EOF
2. Run
./kangaroo -t 8 -gpu -gpuId 0 -w save51.work -wi 300 -o found-51.txt in51.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 2^25 operations where BitCrack runs 2^50.

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 optionsStart from installation
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solved · half the difficulty
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#52
solved · twice the difficulty