Object Oriented Programming

There’s this small up and coming language called java I want to tell you about

Files:

• src.zip

Solution

Extracting from src.zip gives us a bunch of Java files with two-letter names and an rather verbose Main.java file. Each two-letter Java file has several two-letter functions, each returning some other two-letter string. The gist of Main.java is:

• It takes as input a string of length 16 from the user.
• It first converts this input into a new string by XORing each character with a “secure encryption key”, which is the difference between the characters at index 7 and 1 of the canonical name of the encryption key generator class.
  • I don’t have much knowledge of Java, so I guessed this canonical name is Main.EncryptionKeyInstantiator.EncryptionKeyFactory, which would mean the encryption key is 2. Thankfully, I was right :)
• It breaks up the new string into 4 chunks of 4 characters each.
• For each chunk, it encrypts it as follows:
  • From the Java file having the first half of the chunk (of length 2 characters) as its name, it calls the function whose name matches the second half of the chunk.
  • The function in the same Java file whose name matches the return value of the first function is called.
  • The function in the same Java file whose name matches the return value of the second function is called.
  • The return value of the third function is the final encryption of the chunk.
• Once the input is converted into an 8-character string in this manner, it checks if this string equals the package name of scanner (without any punctuation), which I found out is javautil. If so, the user input is the flag.

This sufficiently detailed explanation should be enough to get the flag. The chunks corresponding to ja, va, ut and il were found to be glvg, prpk, qgam and fggg respectively. XORing glvgprpkqgamfggg with 2 gave enterprisecodeee, which was the flag.

Flag

rgbCTF{enterprisecodeee}