Lrep

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

Summary

Walkthrough of the CUSTOM Reversing Lrep. Language: Perl. Source code provided. Program extracts flag characters from a hardcoded string based on XOR condition.

Description

Language: Perl. Source code provided. Program extracts flag characters from a hardcoded string based on XOR condition.

Analysis

 perl read-only • copy allowed Copy
$text = "2I7VjH)Q3RkPK*Sm3R!aY8!1P:5T6YL-`N4U5M,;xB#v1D%24U";
# For each pair of adjacent chars (a, b) in text:
# if ord(a) == (ord(b) ^ 97), then a must match next char of input

The program iterates through pairs of adjacent characters in $text. If ord(a) == ord(b) ^ 97, then character a must match the next input character. ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Solution

Find all positions where the condition is satisfied and collect the characters:

 python read-only • copy allowed Copy
text = "2I7VjH)Q3RkPK*Sm3R!aY8!1P:5T6YL-`N4U5M,;xB#v1D%24U"
flag = ""
for i in range(len(text)-1):
    if ord(text[i]) == (ord(text[i+1]) ^ 97):
        flag += text[i]
# REDACTED

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Key Takeaways / Lessons

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

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Crafted by XESXOR Research • 2026-03-09 • CUSTOM • Lrep • Difficulty: Easy