# PicoCTF 2018 Walkthrough – Crypto Warmups

## Crypto Warmup 1

Category: Cryptography

Points: 75

### 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?.

### 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

In this crypto exercise, we are given 2 strings of text which do not have any meaning among themselves. We are also given a table which we can use to solve the message.

The table has a mapping from a-z characters. We can use the same to solve our challenge. As the two strings are of the same length therefore we can use the table to find out the corresponding letter in respective horizontal and vertical positions.

Going through the table we will get ‘SECRETMESSAGE’ as the mapped message. Enter the same in the text provided and hit submit.

### Solution Flag

picoCTF{SECRETMESSAGE}

## Crypto Warmup 2

Category: Cryptography

Points: 75

### Problem

Cryptography doesn’t have to be complicated, have you ever heard of something called rot13? `cvpbPGS{guvf_vf_pelcgb!}`

### Hint

• This can be solved online if you don’t want to do it by hand!

### Solution

In this problem, we are asked about rot13. Upon googling it we found that its just a cryptography algorithm which shifts a character by its corresponding next 13th letter. Therefore A becomes N, Z becomes M and so on. By applying the cypher twice on the same message we will get the original message back because of 13+13 =26 and there are 26 alphabets in the English. You can learn more about the same here.

Coming to the question we can do it by hand by just shifting each character in the message by 13 places. There are decoders online which can perform the same. One of which you can see here. Enter the decoded message in the text area provided and hit submit.

### Solution Flag

picoCTF{this_is_crypto!}

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