5x5 Crypto
1 minute to read
We are given this set of numbers and characters:
1-3,4-4,2-1,3-1,1-5,1-1,4-2,3-3,{,4-4,2-3,4-5,3-2,1-2,4-3,_,4-5,3-5,}
And we are told that the encryption method takes a 5x5 grid with all letters of the alphabet in order. If we do a quick search, we will find Polybius Square, which is this one:
A | B | C | D | E |
F | G | H | I/J | K |
L | M | N | O | P |
Q | R | S | T | U |
V | W | X | Y | Z |
We can take every pair of i-j
and match it to a letter finding the corresponding row-column cell. For instance, 1-1
is A
and 5-5
is Z
. After decrypting, we get CTFLEARN{THUMBS_UP}
, so the flag will be: CTFlearn{THUMBS_UP}
.