StegCryptoDIY - Final Boss

crypto RSA FCSC 2019 solved on

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Description

As you remember, Dumb and Dumby exchanged messages a few weeks ago by using a new cryptosystem dubbed CryptoDIY based on the problems FACT and DLP.

Recall that the parameters g_1 and g_2 are defined as:

  • N = p . q
  • g_1 = g^(s_1 . (p - 1)) (mod N)
  • g_2 = g^(s_2 . (q - 1)) (mod N) where g is an unknown generator, s_1 and s_2 two nonces, and p and q are unknown as well.

They think they found a hardened version of the cryptosystem: prove them wrong by recovering their shared secret using the information from the two previous challenges StegCrypto DIY - PNG and StegCrypto DIY - RNG.

Note: This challenge has been made for the finale of FCSC 2019.

This challenge has been split into three parts:

Files

  • leHACK19_chall.png
    142.81 KiB – 9bf1385ef8fc2638b90dfaa3d47d4a50ad52b67bf173b052621040f3ce48ca90
  • leHACK19_ref.png
    65.17 KiB – 9151821ba115ed4de102a79695dca76f4994550c6c37068804abe71778c9009e

Author

Guena

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