The ciphertext of this crypto challenge is contained in the file decode.me.The content of the file is:```554545532245{22434223_4223_42212322_55_234234313551_34553131423344}```knowing the format of the flag which is "AFFCTF{}, i started from it mapping the first letters:*  A=55*  F=45*  C=53*   T=22
Analyzing the mapping i understood that it was something similar to a decreasing mapping starting from 55, but with some gaps and i mapped the remaining letters taking the numbers in pairs and, with the following substitutions i came up with the right.
*   E=51*   G=44*   H=43*   I=42*   L=35*   M=34*   N=33*   P=31*   S=23*   U=21
With these substitution the correct key is: **AFFCTF{THIS_IS_IUST_A_SIMPLE_MAPPING}**