Project Sekai
🔒 CrewCTF 2023 / ✅-crypto-nec
nc nec.chal.crewc.tf 20005
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diff_sig1, diff_sig2 = [], []
for i in range(4 - 1):
for j in range(i+1, 4):
diff_sig1.append(sigs[i][1] - sigs[j][1])
diff_sig2.append(sigs[i][0] - sigs[j][0])
a_0, b_0 = diff_sig1[0], diff_sig2[0]
a_1, b_1 = diff_sig1[1], diff_sig2[1]
a_2, b_2 = diff_sig1[2], diff_sig2[2]
a_3, b_3 = diff_sig1[3], diff_sig2[3]
rk = GCD(a_2*b_0 - a_0*b_2, a_0*b_1 - a_1*b_0, a_2*b_1 - a_1*b_2, a_3*b_1 - a_1*b_3, a_3*b_0 - a_0*b_3)
r = int(list(factor(rk))[-1][0])
assert isPrime(r)
print(r)
d and r by the previous partG = (known, ?), where G is actually unknown except that its order is r (edited)
