crypto: interpolation

crypto/interpolation/interpolation/Dockerfile

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+FROM sagemath/sagemath:latest
+
+RUN sudo apt update -y && sudo apt install -y socat
+
+COPY --chown=sage . .
+
+RUN chmod 755 entry.sh chall.sage
+
+EXPOSE ${LISTEN_PORT}
+
+ENTRYPOINT ["/home/sage/entry.sh"]

crypto/interpolation/interpolation/chall.sage

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+#!/usr/bin/sage
+import hashlib
+import re
+
+with open("flag.txt", "rb") as f:
+    FLAG = f.read()
+    assert re.match(rb"Hero{[0-9a-zA-Z_]{90}}", FLAG)
+
+F = FiniteField(2**256 - 189)
+R = PolynomialRing(F, "x")
+H = lambda n: int(hashlib.sha256(n).hexdigest(), 16)
+C = lambda x: [H(x[i : i + 4]) for i in range(0, len(FLAG), 4)]
+
+f = R(C(FLAG))
+
+points = []
+for _ in range(f.degree()):
+    r = F.random_element()
+    points.append([r, f(r)])
+print(points)
+
+flag = input(">").encode().ljust(len(FLAG))
+
+g = R(C(flag))
+
+for p in points:
+    if g(p[0]) != p[1]:
+        print("Wrong flag!")
+        break
+else:
+    print("Congrats!")

crypto/interpolation/interpolation/entry.sh

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+#! /bin/sh
+
+while :
+do
+    socat TCP-LISTEN:${LISTEN_PORT},forever,reuseaddr,fork EXEC:'/home/sage/chall.sage'
+done