VICE: The CIAâs Infamous, Unsolved Cryptographic Puzzle Gets a âFinal Clueâ.
[1]https://www.vice.com/en_us/article/3a8k93/the-cias-infamous-unsolved-cryptogr
aphic-puzzle-gets-a-final-clue

References

   1. https://www.vice.com/en_us/article/3a8k93/the-cias-infamous-unsolved-cryptographic-puzzle-gets-a-final-clue