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Task 11 [Day 5] Reverse engineering A Christmas DOScovery: Tapes of Yule-tide Past.md

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Task 11 [Day 5] Reverse engineering A Christmas DOScovery: Tapes of Yule-tide Past


Screenshot 2023-12-24 at 2 52 06 AM

Learning Objectives

  • Experience how to navigate an unfamiliar legacy system.
  • Learn about DOS and its connection to its contemporary, the Windows Command Prompt.
  • Discover the significance of file signatures and magic bytes in data recovery and file system analysis.

After the machine is up.

Open AC2023.BAK using the MS-DOS Editor and the command

EDIT C:\AC2023.BAK. 

As you can see, the current bytes are set to XX. According to the troubleshooting section we've read, BUMASTER.EXE expects the magic bytes of a file to be 41 43. These are hexadecimal values, however, so we need to convert them to their ASCII representations first.

Go back to the MS-DOS Editor window, move your cursor to the first two characters, remove XX, and replace it with AC. Once that's done, save the file by going to "File > Save".


Screenshot 2023-12-24 at 3 08 47 AM

Now, you can run the command

BUMASTER.EXE C:\AC2023.BAK

Screenshot 2023-12-24 at 3 10 20 AM

Questions:

  1. How large (in bytes) is the AC2023.BAK file?

ANSWER

12,704
  1. What is the name of the backup program?

ANSWER

backupmaster3000
  1. What should the correct bytes be in the backup's file signature to restore the backup properly?

ANSWER

41 43
  1. What is the flag after restoring the backup successfully?

ANSWER

THM{0LD_5CH00L_C00L_d00D}