Rating:

# Crypto Challenge

## dias skeerG tneicna - 20

### Description:
Nothing

### Given:
1 File was given i) decode.me

### Objective:
To decrypt the text provided in "decode.me"

### What to do:
Decrypt the text using any cipher technique

### Tools Required:
Text Editor

### Solution:

Step: Check file format -- success
Command: file decode.me
Output: Just a regular text file with some cipher text
Cipher Text: 554545532245{22434223_4223_42212322_55_234234313551_34553131423344}

Step: Analyze the code manually -- success
Information: 1. Since the format of the string is like "...{...}...", one can easily guess the flag is there and substitution technique is used
2. Comparing cipher text with AFFCTF{...}
3. There is no 0 in the string, maybe 0 is not included
Output: A = 55, F = 45, C = 53, T = 22

Step: Make a table consisting of A-Z with there codes -- failure
Output: A = 55
B = 54
C = 53
D = 52
E = 51
F = 50 ...

Step: Make a table consisting of A-Z with there codes without using 0 -- failure
Output: A = 55
B = 54
C = 53
D = 52
E = 51
F = 45 ...

Step: In previous step we get the code T = 21 and we cannot get a code for Z, So make another table -- success
Information: Playfair cipher uses 25 blocks for A-Z by combining I/J in a single block
Output: A = 55
B = 54
I/J = 42
Z = 11

Step: Crack the cipher simply putting the values
Output: AFFCTF{THIS_IS_JUST_A_SIMPLE_MAPPING}

### Flag:
AFFCTF{THIS_IS_JUST_A_SIMPLE_MAPPING}

Original writeup (https://github.com/I-ikshvaku/writeups/tree/master/2020/affinity_ctf_lite/dias%20skeerG%20tneicna).