diff --git a/tests/device_tests/test_zerosig.py b/tests/device_tests/test_zerosig.py
index 0e1393b80d..2a518830db 100644
--- a/tests/device_tests/test_zerosig.py
+++ b/tests/device_tests/test_zerosig.py
@@ -25,13 +25,6 @@ import common
 
 from trezorlib import messages as proto
 
-if sys.version_info < (3,):
-    def byteindex(data, index):
-        return ord(data[index])
-else:
-    def byteindex(data, index):
-        return data[index]
-
 
 TXHASH_d5f65e = binascii.unhexlify('d5f65ee80147b4bcc70b75e4bbf2d7382021b871bd8867ef8fa525ef50864882')
 
@@ -63,7 +56,7 @@ class TestZeroSig(common.TrezorTest):
 
             tx = self.client.call(msg)
 
-            siglen = byteindex(tx.serialized_tx, 44)
+            siglen = tx.serialized_tx[44]
             print(siglen)
             if siglen < 67:
                 print("!!!!", n)
@@ -89,7 +82,7 @@ class TestZeroSig(common.TrezorTest):
         )
 
         (signatures, serialized_tx) = self.client.sign_tx('Bitcoin', [inp1, ], [out1, ])
-        siglen = byteindex(serialized_tx, 44)
+        siglen = serialized_tx[44]
 
         # TREZOR must strip leading zero from signature
         self.assertEqual(siglen, 67)
@@ -112,7 +105,7 @@ class TestZeroSig(common.TrezorTest):
         )
 
         (signatures, serialized_tx) = self.client.sign_tx('Bitcoin', [inp1, ], [out1, ])
-        siglen = byteindex(serialized_tx, 44)
+        siglen = serialized_tx[44]
 
         # TREZOR must strip leading zero from signature
         self.assertEqual(siglen, 66)
diff --git a/trezorlib/ckd_public.py b/trezorlib/ckd_public.py
index 1aee54e4f3..4ee2244d09 100644
--- a/trezorlib/ckd_public.py
+++ b/trezorlib/ckd_public.py
@@ -32,20 +32,13 @@ from . import messages as proto
 
 PRIME_DERIVATION_FLAG = 0x80000000
 
-if sys.version_info < (3,):
-    def byteindex(data, index):
-        return ord(data[index])
-else:
-    def byteindex(data, index):
-        return data[index]
-
 
 def point_to_pubkey(point):
     order = SECP256k1.order
     x_str = number_to_string(point.x(), order)
     y_str = number_to_string(point.y(), order)
     vk = x_str + y_str
-    return struct.pack('B', (byteindex(vk, 63) & 1) + 2) + vk[0:32]  # To compressed key
+    return struct.pack('B', vk[63] & 1 + 2) + vk[0:32]  # To compressed key
 
 
 def sec_to_public_pair(pubkey):
@@ -152,7 +145,7 @@ def deserialize(xpub):
     node.chain_code = data[13:45]
 
     key = data[45:-4]
-    if byteindex(key, 0) == 0:
+    if key[0] == 0:
         node.private_key = key[1:]
     else:
         node.public_key = key
diff --git a/trezorlib/tools.py b/trezorlib/tools.py
index 4ff3b50e86..9f874d4b5c 100644
--- a/trezorlib/tools.py
+++ b/trezorlib/tools.py
@@ -22,17 +22,6 @@ import binascii
 import struct
 import sys
 
-if sys.version_info < (3,):
-    def byteindex(data, index):
-        return ord(data[index])
-
-    def iterbytes(data):
-        return (ord(char) for char in data)
-else:
-    def byteindex(data, index):
-        return data[index]
-    iterbytes = iter
-
 
 def Hash(data):
     return hashlib.sha256(hashlib.sha256(data).digest()).digest()
@@ -52,8 +41,8 @@ def hash_160_to_bc_address(h160, address_type):
 
 
 def compress_pubkey(public_key):
-    if byteindex(public_key, 0) == 4:
-        return bytes((byteindex(public_key, 64) & 1) + 2) + public_key[1:33]
+    if public_key[0] == 4:
+        return bytes(public_key[64] & 1 + 2) + public_key[1:33]
     raise ValueError("Pubkey is already compressed")
 
 
@@ -73,7 +62,7 @@ def b58encode(v):
     """ encode v, which is a string of bytes, to base58."""
 
     long_value = 0
-    for c in iterbytes(v):
+    for c in v:
         long_value = long_value * 256 + c
 
     result = ''
@@ -86,7 +75,7 @@ def b58encode(v):
     # Bitcoin does a little leading-zero-compression:
     # leading 0-bytes in the input become leading-1s
     nPad = 0
-    for c in iterbytes(v):
+    for c in v:
         if c == 0:
             nPad += 1
         else: