X

Challenge Information

Name: X
Points: 100
Category: Reverse
Objective: Analyze and reverse engineer the application to retrieve the flag.

Solution

Initial Analysis:
- Use tools such as Ghidra, IDA Pro, or Radare2 to analyze the code.
- Upon analysing the application, it performs XOR operations on a specific variable.

Reversing the XOR:

Since XOR is a reversible operation (XOR is its own inverse):
Apply the same XOR key to the modified value to retrieve the original data (flag).

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xor_values = [
    (0x6B, 56),  
    (0x75, 61),  
    (0x65, 38),  
    (0x68, 60),  
    (0x74, 50),  
    (0x69, 91),  
    (0x6F, 91),  
    (0x77, 12),  
]

aBcb4ce08a36317 = "bcb4ce08a3/6317b67`d8`d58e6e1e`b"

decoded_first_part = []
for xor_val, expected in xor_values:
    decoded_first_part.append(chr(expected ^ xor_val)) 

decoded_second_part = []
for char in aBcb4ce08a36317:
    decoded_second_part.append(chr(ord(char) + 1)) 

full_string = ''.join(decoded_first_part) + ''.join(decoded_second_part)

print(f"Full String: {full_string}"+"}")

Flag

Flag: SHCTF24{cdc5df19b407428c78ae9ae69f7f2fac}