![[Hack] picoCTF – Mod 26](https://media.dev.to/cdn-cgi/image/width=800%2Cheight=%2Cfit=scale-down%2Cgravity=auto%2Cformat=auto/https%3A%2F%2Fdev-to-uploads.s3.amazonaws.com%2Fuploads%2Farticles%2Ft75cpwmhrd5l2fctly66.png)
This is a challenge from the picoCTF picoGym, the challenge description follows:
“Cryptography can be easy, do you know what ROT13 is?
cvpbPGS{arkg_gvzr_V’yy_gel_2_ebhaqf_bs_ebg13_uJdSftmh}”
cvpbPGS{arkg_gvzr_V’yy_gel_2_ebhaqf_bs_ebg13_uJdSftmh}”
This is pretty straightforward, we can use a website to decrypt the ROT13 encrypted message.
But in this case, I used a bash script to do this for me. Here’s the script:
# Tring to find a flag using ROT13
# Where $1 is cvpbPGS{arkg_gvzr_V’yy_gel_2_ebhaqf_bs_ebg13_uJdSftmh}
# Where $1 is cvpbPGS{arkg_gvzr_V’yy_gel_2_ebhaqf_bs_ebg13_uJdSftmh}
echo “== ROT13 ==”
echo “”
output=$(echo “$1“ | tr ‘N-ZA-Mn-za-m’ ‘A-Za-z’)
echo “${output}“
The tr command is a substitution command, in this case, we will make the A to be N, B to be O and so on. This is the meaning of ROT13, it will shift each char 13 places:
It’s bidirectional, so no worries of the ordering.
Running the script, the flag is revealed:
Answer:Flag
Flag : picoCTF{next_time_I’ll_try_2_rounds_of_rot13_hWqFsgzu}
