CTF Writeup - ezRSA - Ramadan CTF 2026

The writeup for "ezRSA" from Ramadan CTF 2026 details a cryptography challenge involving RSA decryption without quantum computing. Here's a summary of key points:

1. Challenge Overview: The problem involves decrypting an RSA ciphertext with a given public exponent (e) and modulus (n), but the quantum computing hint is misleading.

2. Solution Approach:

   • Fermat Factorization: Initially attempted, but not applicable here.
   • Wiener's Attack: Exploits small private key (d). The writeup shows how to implement this using continued fractions and checking if derived p and q factors multiply back to n.
   • Pollard's p-1 Algorithm: Another factorization method tried when Wiener fails.
   • FactorDB Query: Checks an online database for precomputed factorizations of the modulus.

3. Key Takeaways:

   • Quantum computing is a red herring in this challenge context.
   • Implementation weaknesses (like small d) can break RSA regardless of key size.
   • Systematically escalate attacks from simple to complex methods.
   • Use automated tools like RsaCtfTool for efficiency.

4. Flag: Not explicitly shown

Read the full article at InfoSec Write-ups - Medium

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