Caesar in the fence score: 10

  • Source: Tianshu Group of BuPT
  • Difficulty: easy
  • Number of participants: 4,531
  • Get Flag: 2,124
  • Number of answers: 2,285
  • Problem solving pass rate: 93%

NlEyQd{seft}

Solution link:

The original link: www.shiyanbar.com/ctf/1867

【 答 案 】

This is the fourth question THAT I started to write in the beginning of cryptography, this question is somewhat interesting, the title is Caesar trapped in the fence, it must be used to fence password and Caesar password, so we first brute force crack this character, then we can use a tool called CTFCrackTools

By the way, I have been using the online decryption tool for a long time, mainly because CTFCrackTools has not been used, and finally found out that the JDK version requires JDK1.8, the mentality exploded, but today I can finally use it. CTFCrackTools in Windows showed A Java Exception has occurred

CTFCrackTools this tool can go to the official website to download, here I will not repeat, need tools partners can also private letter me or message oh ~~~

Here we use the latest version of CTFCrackTools V3.1.3, then we can brute force cracking

The results are as follows:

Crack, found that there are four crack after the fence password, at this time we are stuck in an impasse, how to do?

Small white found a paragraph of very 6 characters, here we briefly introduce the fence password

The so-called fence password is to encrypt the plaintext into a group of N, and then the first word of each group connected to form a paragraph of irregular words. However, there is an unspoken rule in the fence code itself, which is that there are usually not too many letters to make up the fence. (Usually no more than 30, which is one or two sentences)

Very six indicates that the encrypted plaintext is divided into six groups, so at this time we can choose the first fence password to crack the Caesar password

Here, I briefly introduce the Caesar password ~~~

Caesar cipher as one of the oldest symmetric encryption system, was very popular in ancient Rome, his basic idea is: by moving the letter a certain number of digits to achieve encryption and decryption. All letters in the plaintext are replaced with ciphertext after being offset backward (or forward) in the alphabet by a fixed number. For example, when the offset is 3, all letters A will be replaced with D, B will become E, and so on X will become A, Y will become B, and Z will become C. Thus, the bits are the keys to the Encryption and decryption of the Caesar cipher.

So we can do the following:

The results are as follows:

Here we find the word CTF, indicating that this is the answer we need