How Ken Thompson’s Vintage Unix Password Was Finally Cracked

Leah Neukirchen recently reported that the legendary Unix pioneers’ old passwords, stored in a /etc/passwd file extracted from the BSD‑3 source tree, have been exposed.

These passwords are hashed with the DES‑based crypt(3) algorithm, which is weak and limited to eight characters, so Leah attempted to crack them using tools such as John the Ripper and hashcat.

She succeeded in recovering many of the passwords, for example:

gfVwhuAMF0Trw: dmac

Pb1AmSpsVPG0Y: uio

ymVglQZjbWYDE: /.,/.,

c8UdIntIZCUIA: bourne

AAZk9Aj5 / Ue0E: foobar

E9i8fWghn1p / I: apr1744

IIVxQSvq1V9R2: axolotl

9EZLtSYjeEABE: network

P0CHBwE / mB51k: whatnot

... (additional hashes omitted for brevity)

Ken Thompson’s password, however, resisted all attempts; even after exhaustive enumeration of lowercase letters and digits, it remained uncracked. Leah speculated that the password might include uppercase letters or special symbols, which would make a full 7‑character search on modern GPUs take years.

In early October, the discussion resurfaced on the Unix Heritage Society mailing list, where Australian engineer Nigel Williams announced that he finally cracked Ken’s password. The result was:

Ken’s password result: ZghOT0eRm4U9s: p/q2-q4!

The string p/q2-q4! looks like a mathematical formula but actually encodes an old chess notation: “Pawn moves two squares forward; Q stands for Queen.” This reflects Ken’s passion for chess; he was the champion of the 3rd World Computer Chess Championship in 1980 and co‑author of the chess program Belle.

Source: Open Source China Community