diff --git a/py_ecc/bls/api.py b/py_ecc/bls/api.py
index 461a4657..d8d5568a 100644
--- a/py_ecc/bls/api.py
+++ b/py_ecc/bls/api.py
@@ -1,6 +1,4 @@
-from operator import (
-    itemgetter,
-)
+
 from secrets import (
     randbelow,
 )
@@ -9,10 +7,6 @@
     Sequence,
     Tuple,
 )
-
-from cytoolz.itertoolz import (
-    groupby,
-)
 from eth_typing import (
     BLSPubkey,
     BLSSignature,
@@ -92,19 +86,15 @@ def aggregate_pubkeys(pubkeys: Sequence[BLSPubkey]) -> BLSPubkey:
     return G1_to_pubkey(o)
 
 
-def _group_by_messages(
-        message_hashes: Sequence[Hash32],
-        pubkeys: Sequence[BLSPubkey]) -> Iterator[Tuple[Hash32, Tuple[BLSPubkey, ...]]]:
+def _zip(pubkeys: Sequence[BLSPubkey],
+         message_hashes: Sequence[Hash32])-> Iterator[Tuple[BLSPubkey, Hash32]]:
     if len(pubkeys) != len(message_hashes):
         raise ValidationError(
             "len(pubkeys) (%s) should be equal to len(message_hashes) (%s)" % (
                 len(pubkeys), len(message_hashes)
             )
         )
-    groups = groupby(itemgetter(0), zip(message_hashes, pubkeys)).items()
-    for message_hash, group in groups:
-        group_pubkeys = tuple(BLSPubkey(pubkey) for _, pubkey in group)
-        yield Hash32(message_hash), group_pubkeys
+    return zip(pubkeys, message_hashes)
 
 
 def verify_multiple(pubkeys: Sequence[BLSPubkey],
@@ -113,11 +103,12 @@ def verify_multiple(pubkeys: Sequence[BLSPubkey],
                     domain: int) -> bool:
 
     o = FQ12.one()
-    for message_hash, group_pubkeys in _group_by_messages(message_hashes, pubkeys):
-        agg_pub = Z1
-        for key in group_pubkeys:
-            agg_pub = add(agg_pub, pubkey_to_G1(key))
-        o *= pairing(hash_to_G2(message_hash, domain), agg_pub, final_exponentiate=False)
+    for pubkey, message_hash in _zip(pubkeys, message_hashes):
+        o *= pairing(
+            hash_to_G2(message_hash, domain),
+            pubkey_to_G1(pubkey),
+            final_exponentiate=False,
+        )
     o *= pairing(signature_to_G2(signature), neg(G1), final_exponentiate=False)
     final_exponentiation = final_exponentiate(o)
     return final_exponentiation == FQ12.one()
@@ -139,15 +130,11 @@ def verify_multiple_multiple(
 
     random_ints = (1,) + tuple(2**randbelow(64) for _ in signatures[:-1])
     o = FQ12.one()
-    for r_i, pm in zip(random_ints, pubkeys_and_messages):
-        pubkeys, message_hashes = pm
-        for message_hash, group_pubkeys in _group_by_messages(message_hashes, pubkeys):
-            agg_pub = Z1
-            for key in group_pubkeys:
-                agg_pub = add(agg_pub, pubkey_to_G1(key))
+    for r_i, (pubkeys, message_hashes) in zip(random_ints, pubkeys_and_messages):
+        for pubkey, message_hash in _zip(pubkeys, message_hashes):
             o *= pairing(
                 multiply(hash_to_G2(message_hash, domain), r_i),
-                agg_pub,
+                pubkey_to_G1(pubkey),
                 final_exponentiate=False,
             )
     agg_sig = Z2