Слово за слово (Word for Word)

Platform: CUSTOM | Category: Crypto | Type: Challenge | Difficulty: Easy | OS: N/A | **Author: XESXOR Techniques: Character-by-character hash reversal, MD5 rainbow table attack on single characters, Precomputed hash lookup table

Summary

Walkthrough of the CUSTOM Crypto Слово за слово (Word for Word). Task: 43 MD5 hashes separated by spaces. Solution: Each hash is MD5 of a single character; build a lookup table for all printable ASCII characters and decode the flag character by character.

Description

"В школе Вы часто списывали? Если это так, то данное задание не вызовет у Вас трудностей. А тем, кто привык всё делать сам - соболезнуем"

Translation: "Did you often cheat in school? If so, this task won't be difficult for you. And for those who are used to doing everything themselves - our condolences"

Analysis

The file word for word.txt contains a string of 43 MD5 hashes separated by spaces:

0d61f8370cad1d412f80b84d143e1257 f186217753c37b9b9f958d906208506e f623e75af30e62bbd73d6df5b50bb7b5 3a3ea00cfc35332cedf6e5e9a32e94da 9d5ed678fe57bcca610140957afab571 ...

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Key observations:

1. 43 hashes = 43 characters — typical length for a flag in CODEBY{...} format
2. Each hash is 32 hex characters — standard MD5
3. Title "Слово за слово" (Word for Word) — hints at letter-by-letter copying/lookup
4. Description about "cheating" — suggests using precomputed tables (rainbow tables)

Hypothesis: Each MD5 hash is a hash of a single character. We need to create a lookup table for all possible characters and find matches.

Verifying the Hypothesis

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 python read-only • copy allowed Copy
import hashlib

# Check the first hash
test_hash = "0d61f8370cad1d412f80b84d143e1257"

for c in "ABCDEFGHIJKLMNOPQRSTUVWXYZ":
    if hashlib.md5(c.encode()).hexdigest() == test_hash:
        print(f"Found: '{c}'")
        break
# Output: Found: 'C'

The first hash corresponds to the letter 'C' — the beginning of the flag CODEBY!

Solution

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

# Read the file with hashes
with open("word for word.txt", "r") as f:
    content = f.read().strip()

hashes = content.split()
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# Create a lookup table for all possible characters
chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_{}-!@#$%^&*().,;:' "
hash_to_char = {}

for c in chars:
    h = hashlib.md5(c.encode()).hexdigest()
    hash_to_char[h] = c

# Decode each hash
result = []
for h in hashes:
    if h in hash_to_char:
        result.append(hash_to_char[h])
    else:
        result.append('?')  # Unknown character

flag = "".join(result)
print(flag)

Output:

CODEBY{REDACTED}

Alternative Solution: Online Services

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You can use online MD5 rainbow tables:

• https://crackstation.net/
• https://md5decrypt.net/
• https://hashes.com/en/decrypt/hash

Each hash is looked up separately, and the results are combined into a string.

Why This Works

MD5 hash of a single character is easy to crack:

• Only ~95 printable ASCII characters
• All 95 hashes can be precomputed in milliseconds
• Rainbow table for single characters is trivial

Important: This attack works ONLY for hashes of single characters. For hashes of words or phrases, you need full rainbow tables or brute-force. ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Hash Table

Related Techniques

• Rainbow table attack — precomputed hash tables
• Dictionary attack — attack using a wordlist
• Brute-force — exhaustive search
• Hash identification — determining hash type by length/format ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Key Takeaways / Lessons

• Mastering Character-by-character hash reversal, MD5 rainbow table attack on single characters, Precomputed hash lookup table was key to this challenge.
• Always check for common misconfigurations and verify assumptions.

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Crafted by XESXOR Research • 2026-01-02 • CUSTOM • Слово за слово (Word for Word) • Difficulty: Easy