Description
A message was encrypted with a rail fence cipher using 4 rails. Decode it and wrap the plaintext in picoCTF{...}.
Setup
Read the ciphertext from message.txt.
Use CyberChef or another rail fence decoder with key=4 to recover the plain text.
cat message.txt
# In CyberChef: Rail Fence Decode → Key 4 and paste the text
Solution
- Step 1Apply Rail Fence decodingThe challenge states 4 rails, so plug the ciphertext into a rail-fence decoder with key 4. CyberChef’s Rail Fence (Decode) module works great.
- Step 2Wrap the flagThe decoded sentence is already in the picoCTF format; copy it as-is.
Flag
picoCTF{WH3R3_D035_7H3_F3NC3_8361N_4ND_3ND_4A76...}
Rail fence is a simple transposition cipher; once you know the number of rails, decoding is straightforward.