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+# Oblivious Pseudo-Random function
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+
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+# Constructing an OPRF on elliptic curves is possible if the curve is a
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+# prime-order group.
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+Fp = GF(0x40000000000000000000000000000000224698fc094cf91b992d30ed00000001)
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+
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+input_block = Fp(42)
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+
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+# Alice generates a random blinding factor r, and multiplies her input block
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+# with this r
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+r = Fp.random_element()
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+alpha = input_block * r
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+
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+# She sends alpha over to Bob, who has the key k and wants to keep it secret,
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+# so Bob calculates beta from alpha and the key
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+#k = Fp.random_element()
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+k = Fp(69420)
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+beta = alpha * k
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+
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+# And then sends back beta to Alice, who can then unblind the result, by
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+# multiplying beta with 1/r
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+output_block = beta * (1 / r)
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+
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+# If we expand the last calculation we can see how r is eliminated by 1/r
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+# output_block = input_block * r * k * (1/r)
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+# And by cancelling out r and 1/r we get:
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+#output_block = input_block * k
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+print(output_block)
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parazyd