Description
A single text file contains an encrypted string; the challenge name hints at a Caesar/ROT-style cipher. Discover the shift that restores the flag.
Read the provided ciphertext (e.g., xqkwKBN{...}).
Use CyberChef or a local script to apply different ROT shifts until the plaintext forms picoCTF{...}.
wget https://artifacts.picoctf.net/c/354/encrypted.txt && cat encrypted.txt
python3 - <<'PY'
from string import ascii_lowercase
cipher="xqkwKBN{z0bib1wv_l3kzgxb3l_7l140864}"
for shift in range(26):
plain=[]
for ch in cipher:
if 'a' <= ch <= 'z':
plain.append(chr((ord(ch)-97-shift)%26+97))
elif 'A' <= ch <= 'Z':
plain.append(chr((ord(ch)-65-shift)%26+65))
else:
plain.append(ch)
print(shift, ''.join(plain))
PY
Solution
- Step 1Test rotationsShift the alphabet forward/backward until the output reads picoCTF. A shift of 18 decodes the message.
- Step 2Record the decoded flagOnce the plaintext appears, copy the picoCTF string and submit it.
Flag
picoCTF{r0tat1o...d140864}
Any Caesar/ROT decoder works; the correct offset is 18.