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🔒 CrewCTF 2023 / ✅-crypto-pi_is_314
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Sutx BOT 07/07/2023 10:02 PM
pi_is_3.14 - 1000 points
Category: Crypto Description: Area of a quarter circle of radius 1 is pi/4 Let's estimate pi by Monte Carlo simulation! Author : y011d4 nc pi-is-3-14.chal.crewc.tf 20003 Files:Tags: No tags.
07/07/2023 10:02 PM
Sutx pinned a message to this channel. 07/07/2023 10:02 PM
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Sutx BOT 07/07/2023 10:26 PM
@Utaha wants to collaborate 🤝
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Utaha 07/07/2023 10:41 PM
use low bit to gen the floating number
22:42
the state update logic looks like LFSR
22:42
basically each bit is a linear combinatino of the original key
22:46
the way to do this is probably: if the outcome is outside of the circle, then with 90% prob x > 0.5, which means the low bit of n32 is 1
22:47
we have roughly 10000 * (1-pi/4) = 2146 equations
22:47
it should be more than enough since we have only 64 variables (edited)
22:50
gonna go to sleep so feel free to just take it
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Sutx BOT 07/08/2023 12:25 AM
@kanon wants to collaborate 🤝
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Sutx BOT 07/08/2023 2:31 AM
@Violin wants to collaborate 🤝
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Sutx BOT 07/08/2023 6:33 AM
@layka_ wants to collaborate 🤝
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Utaha 07/08/2023 6:43 AM
I'm back
06:44
maybe it might be better to say (x&1, y&1) != (0, 0) for points outside of the circle
06:44
so we can get rid of any probability issues and randomization
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Utaha
used /ctf solve
Sutx BOT 07/08/2023 7:17 AM
✅ Challenge solved.
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