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Challenge 33: (70 Points) Reverse engineer challen...

Создано: 9 октября 2026 г.

Отвечено с использованием GPT-5.6 Thinking от Chat01

Вопрос

challenge3.exe

Challenge 33: (70 Points)
Reverse engineer challenge3.exe on the target machine with the IP address 172.25.65.103 and identify the standard algorithm implemented by the membership validation function.(Answer Format: Xxxx Xxxxxxxxx)
Answer Text
Challenge 34: (30 Points)
Analyze the fiile challenge3.exe and determine the hexadecimal value used as the divisor in its final checksum validation on the machine with the IP address 172.25.65.103.(Answer Format: NxNX)

Ответ

I’ll analyze the uploaded challenge3.exe statically first, focusing on the membership-validation routine and the final checksum comparison. I’ll avoid executing the binary unless static inspection leaves something unresolved.

Мысль

Inspected executable metadata, strings, UPX, and binary analysis tools

Ответ

The executable is a 64-bit Windows PE packed with UPX, so its meaningful code is compressed. I’ve confirmed the packing signature; next I’m unpacking or reconstructing the code section, then I’ll trace the validation math.

Мысль

Decoding bit logic

I’m interpreting getbit as returning the buffer’s top bit while maintaining a sentinel. The main loop appears to build a value from one bit, then read a second bit as a continuation flag; a set flag ends that phase.

Мысль

Analyzed UPX-packed binary structure, decompression, strings, and validation logic

Worked for 1m 46s

Ответ

Challenge 33: Luhn Algorithm
Challenge 34: 0x0A

The validation routine doubles alternating digits from the right, subtracts 9 when the result exceeds 9, sums the digits, then checks whether the checksum is divisible by 10—the standard Luhn Algorithm.

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