@bash — Atbash Cipher

Platform: CUSTOM | Category: Crypto | Type: Challenge | Difficulty: Easy | OS: N/A | **Author: XESXOR Techniques: atbash_decryption

Summary

Walkthrough of the CUSTOM Crypto @bash — Atbash Cipher. Task: Decode Atbash-encrypted text with flag format. Solution: Apply Atbash cipher decryption (A↔Z substitution) to reveal the flag.

Description

Decode the text: HKyXGU{olo_gsrh_rh_zgyzhs}

Analysis

The task name "@bash" is a hint at the Atbash cipher. Atbash is a simple substitution cipher where each letter is replaced with its "mirror" in the alphabet:

• A ↔ Z
• B ↔ Y
• C ↔ X
• etc.

Solution

 python read-only • copy allowed Copy
#!/usr/bin/env python3
def atbash(text):
    result = []
    for c in text:
        if c.isalpha():
            base = ord('A') if c.isupper() else ord('a')
            result.append(chr(base + 25 - (ord(c) - base)))
        else:
            result.append(c)
    return ''.join(result)
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ciphertext = "HKyXGU{olo_gsrh_rh_zgyzhs}"
print(atbash(ciphertext))
# Output: SPbCTF{REDACTED}

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Key Takeaways / Lessons

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

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Crafted by XESXOR Research • 2026-03-08 • CUSTOM • @bash — Atbash Cipher • Difficulty: Easy