The Thirteenth Labour

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The search for the Receda Cube on Earth

The Thirteenth Labour is a puzzle card from the first season of Perplex City, challenging players to brute-force an encryption using distributed computing.

It was solved in 2010 by forum user paraboloid13, who posted the decrypted message to the We Love Puzzles forum in February 2010.[1] They provided some hints but did not explain how they solved the puzzle.

This was the second-to-last solvable Perplex City card, followed by Billion to One, which was solved in 2020. The only remaining card is Riemann.

Perplex City Card Catalog: Season 1 Card #251 - The Thirteenth Labour

Season 1 Card #251 - The Thirteenth Labour


Card text


69 A9 3A FD C5 AD 43 8F 48 53 56 0F

1D 35 3A 8C 5C 44 A6 90 1B 76 46 C7

65 53 C8 A1 E4 B0 40 41 85 2B B7 81

59 E0 D2 39 35 A3 27 3B C3 AF 2E 2E

2F 3B 3B 0B 01 FE 67 51 FE 73 A8 E9

36 0A 93 85 55 2E 9A 4A AE C9 84 CF

18 F8 AB 4D B5 6D 45 07 4E 17 23 A5

7C F1 E8 BD A5 8A BD C8 FE FC DA 2B

6B 71 76 88 1F C0 D1 95 61 8D DB DC

D8 17 2E D7 1D D5 F7 AB AD AB 3E 52

2A 9A 9B BA 37 FE 80 FB 53 95 C9 1D

A2 22 AE 72 85 4A 43 1F 7C 2A BF 2A

79 3A 15 03 8D F2 5B 43 98 90 6D CC

A0 BB E2 A9 6A 52 D1 CB 2B 83 DE D8

BF EC 20 11 70 71 AA 22

Cowhead.gif Cowhead.gif Cowhead.gif Cowhead.gif Cowhead.gif 

Puzzle solution

On February 8, 2010, We Love Puzzles forum user paraboloid13 posted the text of the decrypted message.[1]

Time waits not for beast nor man...

The clock has finally stopped on this puzzle.

This is a tick rather than a tock for completion.


Adrian Hon and Naomi Alderman posted on the forum to confirm that the solution was correct[2].


Parabaloid13's hints

User Parabaloid13 posted several hints about how they reached the solution but never shared a full explanation of their methodology.

12 February 2010 (Archive link):

It was all a matter of time!


15 February 2010 (Archive link):

KingOfWrong - This is not the right method to read this one!

Cabbage - It is not a saying

People forget that time is fluid and in my defence I gave this as much time as it gave me.


18 February 2010 (Archive link):

jack2: Re the pass key - it is indeed 8 characters.

that will remain my secret

The only way to solve this was a forced attack - it took a while - but I have special resources at my disposal - that's all I will say on this matter!

I will drop more hints if they are needed.

So far you have 5 keys that will unlock the mystery - order them wisely - What a steal




The following text is the original content of this wiki page, discussing theories and methods. It is left here for archival purposes. It is unknown how user paraboloid13 solved the puzzle.

The absolute basics

  • We assume a block of text has been scrambled (encrypted) so that we cannot read it
  • the RC5.64 standard refers to how it has been scrambled
  • This scrambling requires a 'Key' to unlock it - we are searching for that key.
  • So there are two camps
    • one camp is supplying thousands of words randomly as keys to see if that produces anything reasonable
    • The other camp is trying to figure out the appropriate word (perhaps using the Labours of Hercules as a clue) then trying that word
  • Of course, if we are wrong about the encryption standard, then we are fairly fubarred, but it would appear that all roads point to it.

  • Of course, there was some speculation that the 12 referred to the fact that there were 12 tasks of Hercules, and 12 RC5 challenges posted by RSA security
    • This was therefore the '13th Challenge'
    • Also, if this does need a brute force or grid computing attack - this would be a 'Herculean Challenge'

The distributed assault is currently underway, see below and at the Assault on 13th Labour site.

Cowheads and 64/12/8

  • The cows represent the symbol of, who first cracked the RC5.64 protocol, possibly indicating that this card requires a simple RC5.64 crack as well
  • However, the card doesn't say RC5.64, it says 64/12/8. The assumption is that:
    • the 5 cow heads is a pointer to the RC5 standards, as worked on by the folks at
    • The 64 would therefore be the encryption standard (RC5.64)
    • The 12 is supposedly the number of rounds, and the key is 8 characters long
    • That is why the brute force using 8 character words and phrases

Distributed Effort

Recently, work has been done by chimera245 to set up a coordinated Grid Computing solve on this Card. There is more information on this here kindly maintained by GuiN. The Grid Client is running nicely and is available here.

Earlier efforts included some work by Scott who did some math, and observed how long it would take to work out an answer here. See: Rccrypt Work Unit checkout for the original proposal for a combined effort.


As of 23-SEP-06, the client has tried every single combination of letters and numbers. That is, every single 8 character combination of the characters: abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789. Nothing has come of this. Basically, this means that the key to unlocking the code HAS to contain at least one symbol. Chimera245 has updated the program, adding 5 more characters to test - <space> . , ? and ! - This will double the size of the possible keyspace.

Card cat title.jpg Please see Brian Enigma's impressive Card Catalog for a sorted, comprehensive listing of cards.