hack(crypto): mock up a hash_to_curve implementation

coordination-layer/crypto.py

@@ -55,6 +55,21 @@ def prf(domain, *elements) -> Field:
     return Field(int(POSEIDON([*_str_to_vec(domain), *elements])))
 
 
+def hash_to_curve(domain, *elements) -> Point:
+    # HACK: we don't currently have a proper hash_to_curve implementation
+    # so we hack the Point.random() function.
+    #
+    # Point.random() calls into the global `random` module to generate a
+    # point. We will seed the random module with the result of hashing the
+    # elements and then call Point.random() to retreive the point
+    # corresponding to the mentioned elements.
+
+    r = prf(f"HASH_TO_CURVE_{domain}", *elements)
+
+    import random
+
+    random.seed(r.v)
+    return Point.random()
 
 
 def comm(*elements):

coordination-layer/test_crypto.py

@@ -0,0 +1,21 @@
+"""
+This module tests that all the hacks we introduced in our crypto mocks give us
+the basic behaviour that we need.
+"""
+
+from unittest import TestCase
+
+
+from crypto import hash_to_curve, Field
+
+
+class TestCrypto(TestCase):
+    def test_hash_to_curve(self):
+        p1 = hash_to_curve(Field(0), Field(1), Field(2))
+        p2 = hash_to_curve(Field(0), Field(1), Field(2))
+
+        assert p1 == p2
+
+        p3 = hash_to_curve(Field(0), Field(1), Field(3))
+
+        assert p1 != p3