ls -al
total 28
drwxr-xr-x 3 root root  4096 Mar 11 20:09 .
drwxr-xr-x 3 root root  4096 Aug 10 14:31 ..
-rw-r--r-- 1 root root    65 Mar 11 20:09 checksum.txt
-rwxr-xr-x 1 root root   856 Mar 11 20:09 decrypt.sh
drwxr-xr-x 2 root root 12288 Mar 11 20:09 files

cat checksum.txt                             
3ad37ed6c5ab81d31e4c94ae611e0adf2e9e3e6bee55804ebc7f386283e366a4

sha256sum files/* | grep "3ad37ed6c5ab81d31e4c94ae611e0adf2e9e3e6bee55804ebc7f386283e366a4"
3ad37ed6c5ab81d31e4c94ae611e0adf2e9e3e6bee55804ebc7f386283e366a4  files/e018b574

./decrypt.sh files/e018b574
Error: 'files/e018b574' is not a valid file. Look inside the 'files' folder with 'ls -R'!

cat decrypt.sh  
        #!/bin/bash

        # Check if the user provided a file name as an argument
        if [ $# -eq 0 ]; then
            echo "Expected usage: decrypt.sh <filename>"
            exit 1
        fi

        # Store the provided filename in a variable
        file_name="$1"

        # Check if the provided argument is a file and not a folder
        if [ ! -f "/home/ctf-player/drop-in/$file_name" ]; then
            echo "Error: '$file_name' is not a valid file. Look inside the 'files' folder with 'ls -R'!"
            exit 1
        fi

        # If there's an error reading the file, print an error message
        if ! openssl enc -d -aes-256-cbc -pbkdf2 -iter 100000 -salt -in "/home/ctf-player/drop-in/$file_name" -k picoCTF; then
            echo "Error: Failed to decrypt '$file_name'. This flag is fake! Keep looking!"
        fi

openssl enc -d -aes-256-cbc -pbkdf2 -iter 100000 -salt -in "files/e018b574" -k picoCTF
picoCTF{trust_but_verify_e018b574}