diff --git a/ChaCha20_Poly1305_64/sim/do_poly_1305.py b/ChaCha20_Poly1305_64/sim/do_poly_1305.py
new file mode 100644
index 0000000..c648483
--- /dev/null
+++ b/ChaCha20_Poly1305_64/sim/do_poly_1305.py
@@ -0,0 +1,54 @@
+from typing import List
+
+def mask_r(r: int) -> int:
+    r_bytes = r.to_bytes(16, "little")
+
+    r_masked = bytearray(r_bytes)
+    r_masked[3] &= 15;
+    r_masked[7] &= 15;
+    r_masked[11] &= 15;
+    r_masked[15] &= 15;
+    r_masked[4] &= 252;
+    r_masked[8] &= 252;
+    r_masked[12] &= 252;
+
+
+    r_masked = int.from_bytes(r_masked, "little")
+
+    return r_masked
+
+
+def poly1305(message: bytes, r: int, s: int):
+    r = mask_r(r)
+    p = 2**130-5
+    acc = 0
+
+    blocks = [int.from_bytes(message[i:i+16], "little") for i in range(0, len(message), 16)]
+
+    for block in blocks:
+        byte_length = (block.bit_length() + 7) // 8
+        
+        block += 1 << (8*byte_length)
+
+        acc = ((acc+block)*r) % p
+
+    acc += s
+
+    return acc & (2**128-1)
+
+    
+def main():
+    r = 0xa806d542fe52447f336d555778bed685
+    s = 0x1bf54941aff6bf4afdb20dfb8a800301
+    
+    golden_result = 0xa927010caf8b2bc2c6365130c11d06a8
+
+    msg = b"Cryptographic Forum Research Group"
+
+    result = poly1305(msg, r, s)
+
+    print(f"{golden_result:x}")
+    print(f"{result:x}")
+
+if __name__ == "__main__":
+    main()