SCSC2026 Quals - ngompor - Reverse Engineering Writeup

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1 minute

SCSC2026 Quals - ngompor - Reverse Engineering Writeup

2026-02-17

Writeup

CTF

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Security

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Reverse Engineering

Category: Reverse Engineering

Flag: SCS26{m4nu4l_h3x_c0mp4r3_is_sneaky}

Challenge Description#

Given a 64-bit ELF executable named ngompor.

Analysis#

After disassembling the binary, we found that the flag data is stored in memory but encoded using a bitwise NOT operation.

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$ objdump -d ngompor -M intel | grep -A 50 "flag_data"

The binary stores encoded bytes that need to be decoded by applying ~byte & 0xFF (bitwise NOT).

Solution#

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# !/usr/bin/env python3
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# Encoded flag data extracted from binary
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encoded_data = [
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    0xac, 0xbc, 0xac, 0xcd, 0xcf, 0x9a, 0xb4, 0xcd,
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    0x91, 0xb7, 0xcd, 0x93, 0x9c, 0x97, 0xb0, 0xb4,
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    0x9c, 0x91, 0x8c, 0xb4, 0xb6, 0x90, 0xb4, 0xb6,
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    0xb0, 0x8c, 0x91, 0x9c, 0x9c, 0x92, 0xb2, 0x86
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]
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# Apply bitwise NOT to decode
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flag = ''.join(chr(~b & 0xFF) for b in encoded_data)
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print(flag)