soal

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.
Additional details will be available after launching your challenge instance.

launch istance

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 64500 ctf-player@rhea.picoctf.net
Using the password 1db87a14. Accept the fingerprint with yes, and ls once connected to begin. \

Remember, in a shell, passwords are hidden!
Checksum: 55b983afdd9d10718f1db3983459efc5cc3f5a66841e2651041e25dec3efd46a
To decrypt the file once you’ve verified the hash, run ./decrypt.sh files/.

hint

• 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.
• You can create a SHA checksum of a file with sha256sum or all files in a directory with sha256sum /*.

• Remember you can pipe the output of one command to another with

  . Try practicing with the ‘First Grep’ challenge if you’re stuck!

solve

ssh -p 64500 ctf-player@rhea.picoctf.net
# pass: 1db87a14

ls
checksum.txt  decrypt.sh  files

./decrypt.sh
# Expected usage: decrypt.sh <filename>

./decrypt.sh checksum.txt
# bad magic number
# Error: Failed to decrypt 'checksum.txt'. This flag is fake! Keep looking!

sha256sum files/* | grep -i "55b983afdd9d10718f1db3983459efc5cc3f5a66841e2651041e25dec3efd46a"
# 55b983afdd9d10718f1db3983459efc5cc3f5a66841e2651041e25dec3efd46a  files/2cdcb2de

./decrypt.sh files/2cdcb2de
# picoCTF{trust_but_verify_2cdcb2de}

flag

picoCTF{trust_but_verify_2cdcb2de}