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basicswap/ed25519_fast_util.py

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+# -*- coding: utf-8 -*-
+
+import secrets
+import hashlib
+import basicswap.contrib.ed25519_fast as edf
+
+
+def get_secret():
+    return 9 + secrets.randbelow(edf.l - 9)
+
+
+def encodepoint(P):
+    zi = edf.inv(P[2])
+    x = (P[0] * zi) % edf.q
+    y = (P[1] * zi) % edf.q
+    y += ((x & 1) << 255)
+    return y.to_bytes(32, byteorder='little')
+
+
+def hashToEd25519(bytes_in):
+    hashed = hashlib.sha256(bytes_in).digest()
+    for i in range(1000):
+        h255 = bytearray(hashed)
+        x_sign = 0 if h255[31] & 0x80 == 0 else 1
+        h255[31] &= 0x7f  # Clear top bit
+        y = int.from_bytes(h255, byteorder='little')
+        x = edf.xrecover(y, x_sign)
+        if x == 0 and y == 1:  # Skip infinity point
+            continue
+
+        P = [x, y, 1, (x * y) % edf.q]
+        # Keep trying until the point is in the correct subgroup
+        if edf.isoncurve(P) and edf.is_identity(edf.scalarmult(P, edf.l)):
+            return P
+        hashed = hashlib.sha256(hashed).digest()
+    raise ValueError('hashToEd25519 failed')