Information

Points	Category	Level
75	Cryptography	Easy

Challenge

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?.

Hint

• Submit your answer in our competition’s flag format. For example, if you answer was ‘hello’, you would submit ‘picoCTF{HELLO}’ as the flag.
• Please use all caps for the message.

Solution

So what we have here? the ciphertext (encoded text) is: llkjmlmpadkkc the key is: thisisalilkey And we got this table:

The length of each key and ciphertext is equal so probably for each char in the plaintext (the original text).
We use the char in the same index in our key and this gives us the ciphertext.
After some searching in google I found an encryption with the name “Vigenère cipher“
and the description of it look the same encryption we use here, and in this encryption they use the same table called “Vigenère square”.

So for being lazy I just used this site in order to decrypt the ciphertext, and got the flag.

Flag

picoCTF{secretmessage}

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