diff --git a/bitcoin/core/_ripemd160.py b/bitcoin/core/_ripemd160.py
new file mode 100644
index 00000000..4b4decbf
--- /dev/null
+++ b/bitcoin/core/_ripemd160.py
@@ -0,0 +1,127 @@
+"""
+ Copyright (c) 2021 Pieter Wuille
+ Distributed under the MIT software license
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy
+ of this software and associated documentation files (the "Software"), to deal
+ in the Software without restriction, including without limitation the rights
+ to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ copies of the Software, and to permit persons to whom the Software is
+ furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in all
+ copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ SOFTWARE.
+"""
+
+"""Pure Python RIPEMD160 implementation."""
+
+# Message schedule indexes for the left path.
+ML = [
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+    7, 4, 13, 1, 10, 6, 15, 3, 12, 0, 9, 5, 2, 14, 11, 8,
+    3, 10, 14, 4, 9, 15, 8, 1, 2, 7, 0, 6, 13, 11, 5, 12,
+    1, 9, 11, 10, 0, 8, 12, 4, 13, 3, 7, 15, 14, 5, 6, 2,
+    4, 0, 5, 9, 7, 12, 2, 10, 14, 1, 3, 8, 11, 6, 15, 13
+]
+
+# Message schedule indexes for the right path.
+MR = [
+    5, 14, 7, 0, 9, 2, 11, 4, 13, 6, 15, 8, 1, 10, 3, 12,
+    6, 11, 3, 7, 0, 13, 5, 10, 14, 15, 8, 12, 4, 9, 1, 2,
+    15, 5, 1, 3, 7, 14, 6, 9, 11, 8, 12, 2, 10, 0, 4, 13,
+    8, 6, 4, 1, 3, 11, 15, 0, 5, 12, 2, 13, 9, 7, 10, 14,
+    12, 15, 10, 4, 1, 5, 8, 7, 6, 2, 13, 14, 0, 3, 9, 11
+]
+
+# Rotation counts for the left path.
+RL = [
+    11, 14, 15, 12, 5, 8, 7, 9, 11, 13, 14, 15, 6, 7, 9, 8,
+    7, 6, 8, 13, 11, 9, 7, 15, 7, 12, 15, 9, 11, 7, 13, 12,
+    11, 13, 6, 7, 14, 9, 13, 15, 14, 8, 13, 6, 5, 12, 7, 5,
+    11, 12, 14, 15, 14, 15, 9, 8, 9, 14, 5, 6, 8, 6, 5, 12,
+    9, 15, 5, 11, 6, 8, 13, 12, 5, 12, 13, 14, 11, 8, 5, 6
+]
+
+# Rotation counts for the right path.
+RR = [
+    8, 9, 9, 11, 13, 15, 15, 5, 7, 7, 8, 11, 14, 14, 12, 6,
+    9, 13, 15, 7, 12, 8, 9, 11, 7, 7, 12, 7, 6, 15, 13, 11,
+    9, 7, 15, 11, 8, 6, 6, 14, 12, 13, 5, 14, 13, 13, 7, 5,
+    15, 5, 8, 11, 14, 14, 6, 14, 6, 9, 12, 9, 12, 5, 15, 8,
+    8, 5, 12, 9, 12, 5, 14, 6, 8, 13, 6, 5, 15, 13, 11, 11
+]
+
+# K constants for the left path.
+KL = [0, 0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xa953fd4e]
+
+# K constants for the right path.
+KR = [0x50a28be6, 0x5c4dd124, 0x6d703ef3, 0x7a6d76e9, 0]
+
+
+def fi(x, y, z, i):
+    """The f1, f2, f3, f4, and f5 functions from the specification."""
+    if i == 0:
+        return x ^ y ^ z
+    elif i == 1:
+        return (x & y) | (~x & z)
+    elif i == 2:
+        return (x | ~y) ^ z
+    elif i == 3:
+        return (x & z) | (y & ~z)
+    elif i == 4:
+        return x ^ (y | ~z)
+    else:
+        assert False
+
+
+def rol(x, i):
+    """Rotate the bottom 32 bits of x left by i bits."""
+    return ((x << i) | ((x & 0xffffffff) >> (32 - i))) & 0xffffffff
+
+
+def compress(h0, h1, h2, h3, h4, block):
+    """Compress state (h0, h1, h2, h3, h4) with block."""
+    # Left path variables.
+    al, bl, cl, dl, el = h0, h1, h2, h3, h4
+    # Right path variables.
+    ar, br, cr, dr, er = h0, h1, h2, h3, h4
+    # Message variables.
+    x = [int.from_bytes(block[4*i:4*(i+1)], 'little') for i in range(16)]
+
+    # Iterate over the 80 rounds of the compression.
+    for j in range(80):
+        rnd = j >> 4
+        # Perform left side of the transformation.
+        al = rol(al + fi(bl, cl, dl, rnd) + x[ML[j]] + KL[rnd], RL[j]) + el
+        al, bl, cl, dl, el = el, al, bl, rol(cl, 10), dl
+        # Perform right side of the transformation.
+        ar = rol(ar + fi(br, cr, dr, 4 - rnd) + x[MR[j]] + KR[rnd], RR[j]) + er
+        ar, br, cr, dr, er = er, ar, br, rol(cr, 10), dr
+
+    # Compose old state, left transform, and right transform into new state.
+    return h1 + cl + dr, h2 + dl + er, h3 + el + ar, h4 + al + br, h0 + bl + cr
+
+
+def ripemd160(data):
+    """Compute the RIPEMD-160 hash of data."""
+    # Initialize state.
+    state = (0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0)
+    # Process full 64-byte blocks in the input.
+    for b in range(len(data) >> 6):
+        state = compress(*state, data[64*b:64*(b+1)])
+    # Construct final blocks (with padding and size).
+    pad = b"\x80" + b"\x00" * ((119 - len(data)) & 63)
+    fin = data[len(data) & ~63:] + pad + (8 * len(data)).to_bytes(8, 'little')
+    # Process final blocks.
+    for b in range(len(fin) >> 6):
+        state = compress(*state, fin[64*b:64*(b+1)])
+    # Produce output.
+    return b"".join((h & 0xffffffff).to_bytes(4, 'little') for h in state)
diff --git a/bitcoin/core/serialize.py b/bitcoin/core/serialize.py
index d181c7d3..e9b85e89 100644
--- a/bitcoin/core/serialize.py
+++ b/bitcoin/core/serialize.py
@@ -20,6 +20,8 @@
 
 from io import BytesIO
 
+from ._ripemd160 import ripemd160
+
 MAX_SIZE = 0x02000000
 
 
@@ -29,9 +31,7 @@ def Hash(msg):
 
 def Hash160(msg):
     """RIPEME160(SHA256(msg)) -> bytes"""
-    h = hashlib.new('ripemd160')
-    h.update(hashlib.sha256(msg).digest())
-    return h.digest()
+    return ripemd160(hashlib.sha256(msg).digest())
 
 
 class SerializationError(Exception):