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I have a task to decrypt custom made transposition cipher, as I'm not the cryptography expert, I would appreciate any help.

I've been given the table of characters ...

M A N B C
D E F G H
I K L O P
Q R S T U
V W X Y Z 

... with images representing:

  • swap
  • up twice
  • left twice

(There's no word about the order of these steps)

The hints are:

  1. MAN
  2. NP = CL

Texts to decode is: ET KO KF


I've tried to fit the steps for getting CL out of NP, but with no luck. Also, there's no sign if the characters are "pushed" while making steps, or the character we're moving is being swapped with the next letter (I'm not even sure if we're moving characters or columns or something else). I know it might seem not explained enough, but as I'm not an expert, I wanted to ask you as it might be some known pattern.

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This looks like a Playfair cipher with MAN as the key.

For characters not in the same row / column, you make a rectangle with the encoded characters at the corners, and the characters in the same row on the opposing sides of the rectangle form the decoded letters. For NP we have -

[N]--B-->C
 F   G   H
 L<--O--[P]

Which yields CL.


So for ET we have -

[E]--F-->G
 K   L   O
 R<--S--[T]

Decoding to GR.

For KO we need a new rule, since K and O are on the same row. For items on the same row we simply shift each letter left one position, wrapping back to the start of the row if needed. This means KO yields

I<--[K] L<--[O]

In other words, KO -> IL.

Finally for KF we have -

 E<--[F]
[K]-->L

Which yields LE

So ET KO KF gives us GRILLE.

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  • $\begingroup$ That is correct. Thank you for your help. I can't imagine myself understanding what I've written better than you :D $\endgroup$ – Dawid Zbiński Feb 27 '18 at 21:36

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