Problem: Crpyto can often be done by hand, here’s a message you got from a friend, llkjmlmpadkkc with the key of thisisalilkey. Can you use this table to solve it?.
File: The table
Solution: This is a Vigenere cipher. You can use the table for you can use an online solver. Like https://www.boxentriq.com/code-breaking/vigenere-cipher.
Flag: picoCTF{SECRETMESSAGE}