Verify

Challenge Description

People keep trying to trick my players with imitation flags. I want to make sure they get the real thing! I’m going to provide the SHA-256 hash and a decrypt script to help you know that my flags are legitimate.

ssh -p 52595 ctf-player@rhea.picoctf.net

Using the password 84b12bae. Accept the fingerprint with yes, and ls once connected to begin. Remember, in a shell, passwords are hidden!

Checksum: 3ad37ed6c5ab81d31e4c94ae611e0adf2e9e3e6bee55804ebc7f386283e366a4 To decrypt the file once you’ve verified the hash, run ./decrypt.sh files/. Additional details will be available after launching your challenge instance.

Approach and Steps

Try to decrypt a random file with the given script which returned gibberish.

• View the hints
  • Hint 1
    • Checksums let you tell if a file is complete and from the original distributor. If the hash doesn’t match, it’s a different file.
  • Hint 2
    • You can create a SHA checksum of a file with sha256sum or all files in a directory with sha256sum /*.
  • Hint 3
    • Remember you can pipe the output of one command to another with |. Try practicing with the ‘First Grep’ challenge if you’re stuck!

sha256sum files/* gave shecksum of all files

checksum files/* | grep 3ad37ed6c5ab81d31e4c94ae611e0adf2e9e3e6bee55804ebc7f386283e366a4 gave the file in which the flag exist.

Flag

Flag

picoCTF{trust_but_verify_e018b574}

Tools Used

ssh grep Pipe Operator sha256sum