Rating:
# 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 text
flag = "cvpbPGS{arkg_gvzr_V'yy_gel_2_ebhaqf_bs_ebg13_MAZyqFQj}"
# A-Z
AZ = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
# a-z
az = "abcdefghijklmnopqrstuvwxyz"
# string to store result
s = ""
# iterate through encrypted flag
for 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 string
print(s)
```
Once run we get:
```
picoCTF{next_time_I'll_try_2_rounds_of_rot13_ZNMldSDw}
```
