NCS Competition 2021 Writeup
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NCS Competition 2021 Writeup
HHousen National Cyber Scholarship Competition 2021 Writeup
Forensics
Crypto
CM01 - 250pts
CM02 - 250pts
CX01 - 1000pts
CH01 - 500pts
CH02 - 500pts
Binary
Networking
Web
Challenge Name
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CH01 - 500pts

Briefing

Download the files and find a way to retrieve the encrypted data. Contents: 1.pub, 2.pub, m1.enc, m2.enc
Challenge Files:

Solution

  1. 1.
    Searching for "rsa two messages different exponents" finds this Crypto StackExchange answer which links to this other Crypto StackExchange answer which mentions a "common modulus attack."
  2. 2.
    ​Mathematical Attacks on RSA Cryptosystem states: "A Common Modulus attack can be used to recover the plaintext when the same message is encrypted to two RSA keys that use the same modulus. This algorithm works if and only if message sends with the same modulus and relatively prime encryption exponents." You can learn more by reading this article RSA Attacks: Common Modulus.
  3. 3.
    Searching for a Python script to conduct this attack finds HexPandaa/RSA-Common-Modulus-Attack.
  4. 4.
    We can run this tool using python3 rsa-cm.py -c1 ch01/m1.enc -c2 ch01/m2.enc -k1 ch01/1.pub -k2 ch01/2.pub to get the flag: Flag: shaRinGisCaRinG-010.

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shaRinGisCaRinG-010
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CH02 - 500pts
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Briefing
Solution
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