diff --git a/trezorlib/tools.py b/trezorlib/tools.py
index 9f874d4b5c..4ff3b50e86 100644
--- a/trezorlib/tools.py
+++ b/trezorlib/tools.py
@@ -22,6 +22,17 @@ 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()
@@ -41,8 +52,8 @@ def hash_160_to_bc_address(h160, address_type):
 
 
 def compress_pubkey(public_key):
-    if public_key[0] == 4:
-        return bytes(public_key[64] & 1 + 2) + public_key[1:33]
+    if byteindex(public_key, 0) == 4:
+        return bytes((byteindex(public_key, 64) & 1) + 2) + public_key[1:33]
     raise ValueError("Pubkey is already compressed")
 
 
@@ -62,7 +73,7 @@ def b58encode(v):
     """ encode v, which is a string of bytes, to base58."""
 
     long_value = 0
-    for c in v:
+    for c in iterbytes(v):
         long_value = long_value * 256 + c
 
     result = ''
@@ -75,7 +86,7 @@ def b58encode(v):
     # Bitcoin does a little leading-zero-compression:
     # leading 0-bytes in the input become leading-1s
     nPad = 0
-    for c in v:
+    for c in iterbytes(v):
         if c == 0:
             nPad += 1
         else: