Reply To: The official Challenge 9B hints thread
@momo, #92710
The keywords (in my experience) were NOTHING (keystream) and ZERO (square). This was done in the following way. ZERO was arranged in a square as shown:
_12345
1ZEROP
2QSTUV
3WXYAB
4CDFGH
5IKLMN
And each letter was substituted for a two-digit number in the form (row,column). (So Z=11,E=12,etc. I=J=51.)
Now NOTHING can be encrypted as:
55-14-23-45-51-55-44
This string of seven numbers was repeated to match the length of the ciphertext and then added to the relevant numbers in the encrypted plaintext. So the start of the message is encrypted:
Plaintext_ – _D _E _A _R __M _R …
Polybius__ – 42 12 34 13 _54 13 …
Keystream_ – 55 14 23 45 _51 55 …
Ciphertext – 97 26 57 58 105 68 …