128 is new black — RSA Factorization

Platform: spbctf | Category: Crypto | Type: Challenge | Difficulty: Easy | OS: NA | Author: XESXOR | Date: 2026-03-08 | Status: Solved Techniques: rsa_factorization_online

Summary

Task: Factorize a 128-bit RSA modulus. Solution: Use online factorization service (factordb.com) to get the prime factors.

128 is new black — Crypto Kids 2.0

Description

Factorize n = 203412571701246538324790493908119368569. Answer is any factor.

Analysis

A 128-bit number is easily factorized using online services (factordb.com) or local tools (yafu, msieve).

Solution

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

n = 203412571701246538324790493908119368569

# Using factordb API
url = f"http://factordb.com/api?query={n}"
response = requests.get(url)
data = response.json()

# Or directly:
# p = REDACTED
# q = 15727497203256431323
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p = REDACTED
q = 15727497203256431323

assert p * q == n
print(f"p = {p}")
print(f"q = {q}")

# Flag is any of the factors
print(f"Flag: {p}")

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