Artist James Sanborn created the sculpture Kryptos in 1989, which sits at the CIA headquarters and contains a coded message that has never been fully solved.
While three of the four sections of the ciphertext have been decoded, the final section, known as K4, has never been solved, and only Sanborn knows the solution.
Now, Sanborn has announced he is selling the solution to the 97-character plaintext of K4, as well as a curved metal plate that he used as a cutting sample for the panel.
The artist has said he is selling the solution to K4 in part because he needs the money, and also because he is frustrated at inaccuracies about the code being spread by those using artificial intelligence to try and crack it.
It is hoped that the winning bidder for the code will then take over answering queries from the active community that is still trying to crack the code.
