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Daily AlpacaHack

A daily CTF challenge with a fun new puzzle every day

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We publish one simple, beginner-friendly or educational CTF challenge every day!

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Today's Challenge
minaminaominaminao
Even Worse RSA
Crypto
Hard
15 solves
Submissions (latest 3)
tsukuyomi-chan

SOLVED!

May 22, 7:46 PM

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admin
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Writeups

tadanobutubutu

Writeup for Time Travelers' OTP

tadanobutubutu

ja
Time Travelers' OTP

23 minutes ago

Daily AlpacaHackに挑戦するつくよみちゃん 05/21 misc/Python: Impossible/kakur41

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Writeup for Python:Impossible

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tadanobutubutu

Writeup for Small d

ja

2026/05/19 16:03

Rows:

Even Worse RSA

Topic: Number TheoryReleased: May 23, 2026

15 solves
Crypto
Hard

by

minaminao

minaminao

It seems one-p-rsa has been defeated ...

Beginner Hint 1 (AI-translated)
  • Unlike one-p-rsa, the exponent e is changed from 65537 to 65538.
  • As a result, the naive solution for one-p-rsa no longer works.
  • First, think about why the original approach stops working.
Beginner Hint 2 (AI-translated)
  • In one-p-rsa, p-1 and e were coprime, so it was possible to compute the inverse of e modulo p-1.
  • This challenge is different. Since e factors as 2 * 3^2 * 11 * 331, gcd(e, p-1) is even. It also has about a 1/2 chance to be a multiple of 3, because p-1 mod 3 is either 0 or 1.
  • In this case, how can we solve it?
  • By leveraging SageMath, you can solve it more easily.
even-worse-rsa.tar.gz

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