Условный реверс (Conditional Reverse)

Platform: bug-makers | Category: Misc | Type: Challenge | Difficulty: Easy | OS: Linux | Author: XESXOR | Date: 2026-05-25 | Status: Solved Techniques: ascii_code_arithmetic, cell_dependency_resolution, xlsx_conditional_formatting_extraction

Summary

Task: Google Spreadsheet with conditional formatting rules on empty cells; reconstruct the flag by satisfying all rules. Solution: export as xlsx, parse conditional formatting with openpyxl, solve ASCII code arithmetic and cell dependency chains.

Условный реверс (Conditional Reverse) — Bug Makers CTF

Description

Нужно восстановить все символы флага так, чтобы они соответсвовали правилам условного форматирования в гугловой таблице. Ссылка на таблицу: https://docs.google.com/spreadsheets/d/14_eCC-Qyse0uUgxdm8yl5HDIJz9Jrqy7ZcdB7K_Na6Y/edit?gid=0#gid=0

English summary: A Google Spreadsheet titled "Реверс в экселе" (Reverse in Excel) contains conditional formatting rules on row 15. Some cells are pre-filled (BugCTF{...}), while cells F15–O15 are empty. The goal is to determine what value each empty cell must contain to satisfy its conditional formatting rule, thereby reconstructing the flag. ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Analysis

Row 15 of the spreadsheet contains the flag spread across cells C15 through P15:

• Pre-filled cells: C15="Bug", D15="CTF", E15="{", P15="}"
• Empty cells to solve: F15 through O15

Each cell has a conditional formatting rule that turns the cell green (or applies some visual indicator) when the correct value is entered. The rules use various Google Sheets formula constructs:

• Direct equality checks (cellIs equal)
• String prefix matching (beginsWith)
• Numeric range constraints (AND(x>2, x<4))
• ASCII code arithmetic (CODE(), CHAR())
• Cross-cell references creating dependency chains ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

The key insight is that some cells depend on other cells' values, creating a dependency graph that must be resolved in the correct order.

Solution

Step 1: Export the spreadsheet as .xlsx

Google Sheets conditional formatting rules are not visible in CSV exports but are preserved in xlsx format:

 bash read-only • copy allowed Copy
curl -L "https://docs.google.com/spreadsheets/d/14_eCC-Qyse0uUgxdm8yl5HDIJz9Jrqy7ZcdB7K_Na6Y/export?format=xlsx" -o spreadsheet.xlsx

Step 2: Extract conditional formatting rules

 python read-only • copy allowed Copy
#!/usr/bin/env python3
import openpyxl
‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

wb = openpyxl.load_workbook('spreadsheet.xlsx')
ws = wb.active

# Extract all conditional formatting rules
for cf in ws.conditional_formatting:
    for rule in cf.rules:
        cells = str(cf)
        print(f"Cells: {cells}")
        print(f"  Type: {rule.type}")
        print(f"  Operator: {rule.operator}")
        print(f"  Formula: {rule.formula}")
        print(f"  Text: {rule.text}")
        print()

Step 3: Solve each cell's rule

Solving order matters — start with cells that have direct constraints, then resolve dependent cells. ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Phase 1: Direct constraints (no dependencies)

Phase 2: Dependent cells (resolved using Phase 1 values)

Step 4: Assemble the flag

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

C15  D15  E15  F15  G15  H15  I15  J15  K15  L15  M15  N15  O15  P15
Bug  CTF  {    s    h    3    3    t    s    _    r    e    v    }

Flag: BugCTF{REDACTED}

The flag content "sh33ts_rev" is leetspeak for "sheets_rev" (sheets reverse), a wordplay on the challenge theme of reverse-engineering Google Sheets conditional formatting. ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍