Project Sekai - ✅-crypto-nec

nec_easy - 1000 points

Category: Crypto Description: Can we factor N which is related to EC ? Author : kiona nc nec-easy.chal.crewc.tf 20006 Files:

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Sutx pinned a message to this channel. 07/07/2023 10:02 PM

@Utaha wants to collaborate

@kanon wants to collaborate

@Violin wants to collaborate

@Aptx wants to collaborate

06:22

@layka_ wants to collaborate

anyone good with lattices here ?

07:56

(sig2_j - sig2_i) * nonce - (sig1_j - sig1_i) * d = 0 mod r

07:56

we have 7 equations of that

07:56

with unknown modulus

what is known?

sig2 sig1 (edited)

08:08

2.07 KB

08:08

thinking of this form

so I guess it's a * nonce = b * d mod r, where a, b is known?

yep

let's say you can have a1, b1, a2, b2, (edited)

08:09

then a1b2-a2b1 is a multiple of r

08:09

so you can take gcd of all a1b2-a2b1 and get r

08:09

nonce and d is trivial afterward

08:09

tho you only get the ratio (edited)

Utaha

then a1b2-a2b1 is a multiple of r

i always forget abt this trick

lmao

i'll go for that

solved

layka_

used /ctf solve

✅ Challenge solved.