The beneath is the cipher that’s to be cracked:

40 77 77 60 6b 6e 29 69 73 19 6b 69 75 6d 2f 29 67 30 7c 73 75 6e 75 2c 70 20 74 26 74 68 6b 6c 70 67 66 27 66 28 69 5e 27 7a 68 63 6b 82 27 29 28 -de


  • -de is a termination character and isn’t a part of the message.
  • this ciphertext is in hexadecimal (base 16)
  • ASCII values have been used together with a number of shifts to derive the cipher-text.


Clues are in descending order of how a lot they reveal. Read solely until the place essential.

  • A most of 8 shifts are doable which can or could not have distinctive values. The precise variety of shifts used could or might not be lesser than 8, it will depend on sure mounted guidelines.

  • the precise shift for use relies upon upon the place of the char.

  • mathematical number-series are used together with place worth to find out shift used.

  • 6 such sequence are used, of which 2 concern form, and two are among the hottest.

  • The two lesser recognized sequence are the Catalan quantity sequence and the Lucas quantity sequence.

  • If not one of the 6 sequence are glad, place is checked for odd/even.

  • All six sequence are – Catalan , Fibonacci, Lucas, Pentagon, Hexagon, Prime, and if not odd/even.

  • These sequence are checked one after the opposite, and if a match is discovered, the following will not be checked.

  • Finally, that is the C implementation of the methodology used to generate this cipher.

This cipher textual content as effectively its C implementation have modified since this query was posted, nonetheless, the hyperlink to it nonetheless redirects to v2.0. It is at the moment at v3.0 , which you will take a look at right here.




The plaintext is:

Attack at daybreak, _(uknow-i'm-kidding)_ be reddy !!


For every character, examine if the 0-based index of this char throughout the ciphertext is a part of the Catalan, Fibonacci, Lucas, Pentagonal, Hexagonal, or Prime numbers (in that precise order). If not, examine if the index is even or odd. For every of those 8 teams a hard and fast shift throughout the ASCII vary is outlined. The shift values for these 8 will be regarded as the ‘key’.

To break the cipher, I analyzed the ciphertext values for every group and tried out shifts that appear cheap. For instance, the beginning of the ciphertext “40 77 77 60 6b 6e 29 69 73 19 6b 69 75″ closely means that 0x29 and 0x19 are areas, because the numbers are so low and an area is 0x20 in ASCII. Letter frequency and letter patterns (particularly at “ATTACK”) additionally got here into play.

The shifts are:
Catalan: -3
Fibonacci: +1
Lucas: -8
Pentagon: +2
Hexagon: -9
Prime: +1
Even: -7
Odd: +7