Mic Check Five

Platform: CUSTOM | Category: Reversing | Type: Challenge | Difficulty: Easy | OS: N/A | **Author: XESXOR Techniques: arithmetic_reverse, source_code_analysis

Summary

Walkthrough of the CUSTOM Reversing Mic Check Five. Language: C. Source code provided. Flag checker with positional shift encoding.

Description

Language: C. Source code provided. Flag checker with positional shift encoding.

Analysis

Verification algorithm:

 c read-only • copy allowed Copy
char serial[] = "f2hwldozg|:wbq";
for (i = 0; i < strlen(serial); i++) {
    if (input[i] + i != serial[i]) { /* wrong */ }
}

Solution

Reverse operation: input[i] = serial[i] - i

 python read-only • copy allowed Copy
serial = "f2hwldozg|:wbq"
flag = ''.join(chr(ord(c) - i) for i, c in enumerate(serial))
# REDACTED

‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Key Takeaways / Lessons

• Mastering arithmetic_reverse, source_code_analysis was key to this challenge.
• Always check for common misconfigurations and verify assumptions.

---

Crafted by XESXOR Research • 2026-03-09 • CUSTOM • Mic Check Five • Difficulty: Easy