One of the 160 puzzle addresses created in 2015 to show how hard it is to guess a Bitcoin private key. This one still stands, with 13.8 BTC (about $901,402) waiting for whoever finds the key.
1Ab4vzG6wEQBDNQM1B2bvUz4fqXXdFk2WTThe private key of this address is a number between 2137 and 2138, which is 1.7 × 1041 possible keys. In hex, the range looks like this:
200000000000000000000000000000000003ffffffffffffffffffffffffffffffffffffFor scale: one modern GPU checking about a billion keys per second would need about 1025 years to sweep this entire range.
This demo samples random keys inside the exact range of this puzzle, right in your browser. Every candidate is real, but at JavaScript speed the odds of landing on the key are astronomically small. It exists to give you a feel for the scale, not to win the prize. Dedicated GPU tools scan roughly a thousand times faster, and the full table on the home page explains what to do in the absurdly lucky case that a search actually hits.
In 2015, an anonymous user created 160 Bitcoin addresses and funded them with about 1000 BTC in total. Each address hides its private key in a range that doubles with every puzzle number: puzzle 1 uses a 1 bit range, puzzle 160 a 160 bit range. Puzzle 138 sits at the 138 bit mark, so its key is one of 1.7 × 1041 candidates.
Nobody has found this key yet, and the address has never sent a transaction, so its public key stays hidden. That leaves plain brute force as the only line of attack: checking keys one by one until the derived address matches. One modern GPU at about a billion keys per second would need about 1025 years to sweep the whole range, and even large farms only shave that down linearly. The prize simply sits there until hardware, luck, or a breakthrough catches up.
The whole series is best understood as a public experiment, not a hacking contest. These coins were placed on purpose to be found, and the solved and unsolved puzzles together map the exact frontier of what today's hardware can do against Bitcoin's cryptography. Guessing the key of a normal wallet remains astronomically out of reach: a real 256 bit key has a keyspace about 1029 times larger than even puzzle 160. Read more about the math and the quantum angle in the FAQ on the main page.