# picoCTF Mod 26 Write Up
## Details:Points: 10
Jeopardy style CTF
Category: Cryptography
Comments:
Cryptography can be easy, do you know what ROT13 is? ```cvpbPGS{arkg_gvzr_V'yy_gel_2_ebhaqf_bs_ebg13_MAZyqFQj}```
## Write up:
ROT13 is a cipher that rotates each character 13 letters over. The mod 26 is a hint about looping back around. You can use an online decoder but since I'm trying to explain things a bit more here I decided to make a small script to decode this:
```python# initial encrypted textflag = "cvpbPGS{arkg_gvzr_V'yy_gel_2_ebhaqf_bs_ebg13_MAZyqFQj}"
# A-ZAZ = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
# a-zaz = "abcdefghijklmnopqrstuvwxyz"
# string to store results = ""
# iterate through encrypted flagfor x in flag:    # if the character is in AZ	if x in AZ:        # go 13 characters further from the current character		s += AZ[(AZ.index(x)+13)%len(AZ)]    	# if the character is in az	elif x in az:        # go 13 characters further from the current character		s += az[(az.index(x)+13)%len(az)]	else:        # else add the character		s += x
# print stringprint(s)```
Once run we get:
```picoCTF{next_time_I'll_try_2_rounds_of_rot13_ZNMldSDw}```