diff --git a/jmbitcoin/jmbitcoin/__init__.py b/jmbitcoin/jmbitcoin/__init__.py
index 209bc1d..ac763cc 100644
--- a/jmbitcoin/jmbitcoin/__init__.py
+++ b/jmbitcoin/jmbitcoin/__init__.py
@@ -1,3 +1,6 @@
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import *
 import coincurve as secp256k1
 from jmbitcoin.secp256k1_main import *
 from jmbitcoin.secp256k1_transaction import *
diff --git a/jmbitcoin/jmbitcoin/bci.py b/jmbitcoin/jmbitcoin/bci.py
index 6eda124..37ca2a9 100644
--- a/jmbitcoin/jmbitcoin/bci.py
+++ b/jmbitcoin/jmbitcoin/bci.py
@@ -1,4 +1,7 @@
 #!/usr/bin/python
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 import json, re
 import random
 import time
diff --git a/jmbitcoin/jmbitcoin/bech32.py b/jmbitcoin/jmbitcoin/bech32.py
index 45e65ce..36f3202 100644
--- a/jmbitcoin/jmbitcoin/bech32.py
+++ b/jmbitcoin/jmbitcoin/bech32.py
@@ -19,7 +19,9 @@
 # THE SOFTWARE.
 
 """Reference implementation for Bech32 and segwit addresses."""
-
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 
 CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
 
diff --git a/jmbitcoin/jmbitcoin/btscript.py b/jmbitcoin/jmbitcoin/btscript.py
index c658c4e..4ef74be 100644
--- a/jmbitcoin/jmbitcoin/btscript.py
+++ b/jmbitcoin/jmbitcoin/btscript.py
@@ -1,3 +1,6 @@
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 #OP codes; disabled commented.
 
 # push value
diff --git a/jmbitcoin/jmbitcoin/secp256k1_deterministic.py b/jmbitcoin/jmbitcoin/secp256k1_deterministic.py
index c1d3436..1407769 100644
--- a/jmbitcoin/jmbitcoin/secp256k1_deterministic.py
+++ b/jmbitcoin/jmbitcoin/secp256k1_deterministic.py
@@ -1,6 +1,10 @@
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import *
 from jmbitcoin.secp256k1_main import *
 import hmac
 import hashlib
+import struct
 
 # Below code ASSUMES binary inputs and compressed pubkeys
 MAINNET_PRIVATE = b'\x04\x88\xAD\xE4'
@@ -32,29 +36,30 @@ def raw_bip32_ckd(rawtuple, i):
                      hashlib.sha512).digest()
 
     if vbytes in PRIVATE:
-        newkey = add_privkeys(I[:32] + B'\x01', priv, False)
+        newkey = add_privkeys(I[:32] + b'\x01', priv, False)
         fingerprint = bin_hash160(privtopub(key, False))[:4]
     if vbytes in PUBLIC:
-        newkey = add_pubkeys([privtopub(I[:32] + '\x01', False), key], False)
+        newkey = add_pubkeys([privtopub(I[:32] + b'\x01', False), key], False)
         fingerprint = bin_hash160(key)[:4]
 
     return (vbytes, depth + 1, fingerprint, i, I[32:], newkey)
 
 def bip32_serialize(rawtuple):
     vbytes, depth, fingerprint, i, chaincode, key = rawtuple
-    i = encode(i, 256, 4)
-    chaincode = encode(hash_to_int(chaincode), 256, 32)
+    if isinstance(i, int):
+        i = struct.pack(b'>L', i)
+    chaincode = chaincode
     keydata = b'\x00' + key[:-1] if vbytes in PRIVATE else key
     bindata = vbytes + from_int_to_byte(
         depth % 256) + fingerprint + i + chaincode + keydata
-    return changebase(bindata + bin_dbl_sha256(bindata)[:4], 256, 58)
+    return b58encode(bindata + bin_dbl_sha256(bindata)[:4])
 
 def bip32_deserialize(data):
-    dbin = changebase(data, 58, 256)
+    dbin = b58decode(data)
     if bin_dbl_sha256(dbin[:-4])[:4] != dbin[-4:]:
         raise Exception("Invalid checksum")
     vbytes = dbin[0:4]
-    depth = from_byte_to_int(dbin[4])
+    depth = dbin[4]
     fingerprint = dbin[5:9]
     i = decode(dbin[9:13], 256)
     chaincode = dbin[13:45]
diff --git a/jmbitcoin/jmbitcoin/secp256k1_main.py b/jmbitcoin/jmbitcoin/secp256k1_main.py
index fa73fc0..c2a698a 100644
--- a/jmbitcoin/jmbitcoin/secp256k1_main.py
+++ b/jmbitcoin/jmbitcoin/secp256k1_main.py
@@ -1,96 +1,221 @@
 #!/usr/bin/python
-from __future__ import print_function
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
+from future.utils import bytes_to_native_str
 import binascii
 import hashlib
-import re
 import sys
 import base64
+import struct
 import coincurve as secp256k1
 
 #Required only for PoDLE calculation:
 N = 115792089237316195423570985008687907852837564279074904382605163141518161494337
 
 #Standard prefix for Bitcoin message signing.
-BITCOIN_MESSAGE_MAGIC = '\x18' + 'Bitcoin Signed Message:\n'
-
-if sys.version_info.major == 2:
-    string_types = (str, unicode)
-    string_or_bytes_types = string_types
-    int_types = (int, float, long)
-
-    # Base switching
-    code_strings = {
-        2: '01',
-        10: '0123456789',
-        16: '0123456789abcdef',
-        32: 'abcdefghijklmnopqrstuvwxyz234567',
-        58: '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',
-        256: ''.join([chr(x) for x in range(256)])
-    }
-
-    def lpad(msg, symbol, length):
-        if len(msg) >= length:
-            return msg
-        return symbol * (length - len(msg)) + msg
-
-    def get_code_string(base):
-        if base in code_strings:
-            return code_strings[base]
+BITCOIN_MESSAGE_MAGIC = b'\x18' + b'Bitcoin Signed Message:\n'
+
+string_types = (str)
+string_or_bytes_types = (str, bytes)
+int_types = (int, float)
+
+# Base switching
+code_strings = {
+    2: '01',
+    10: '0123456789',
+    16: '0123456789abcdef',
+    32: 'abcdefghijklmnopqrstuvwxyz234567',
+    58: '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',
+    256: ''.join([chr(x) for x in range(256)])
+}
+
+def lpad(msg, symbol, length):
+    if len(msg) >= length:
+        return msg
+    return symbol * (length - len(msg)) + msg
+
+def get_code_string(base):
+    if base in code_strings:
+        return code_strings[base]
+    else:
+        raise ValueError("Invalid base!")
+
+def bin_to_b58check(inp, magicbyte=b'\x00'):
+    if not isinstance(magicbyte, int):
+        magicbyte = struct.unpack(b'B', magicbyte)[0]
+    assert(0 <= magicbyte <= 0xff)
+    if magicbyte == 0:
+        inp_fmtd = struct.pack(b'B', magicbyte) + inp
+    while magicbyte > 0:
+        inp_fmtd = struct.pack(b'B', magicbyte % 256) + inp
+        magicbyte //= 256
+    checksum = bin_dbl_sha256(inp_fmtd)[:4]
+    return b58encode(inp_fmtd + checksum)
+
+def bytes_to_hex_string(b):
+    return b.encode('hex')
+
+def safe_from_hex(s):
+    return s.decode('hex')
+
+def from_int_to_byte(a):
+    return struct.pack(b'B', a)
+
+def from_byte_to_int(a):
+    return struct.unpack(b'B', a)[0]
+
+def from_string_to_bytes(a):
+    return a if isinstance(a, bytes) else bytes(a, 'utf-8')
+
+def safe_hexlify(a):
+    return str(binascii.hexlify(a), 'utf-8')
+
+class SerializationError(Exception):
+    """Base class for serialization errors"""
+
+
+class SerializationTruncationError(SerializationError):
+    """Serialized data was truncated
+    Thrown by deserialize() and stream_deserialize()
+    """
+
+def ser_read(f, n):
+    """Read from a stream safely
+    Raises SerializationError and SerializationTruncationError appropriately.
+    Use this instead of f.read() in your classes stream_(de)serialization()
+    functions.
+    """
+    MAX_SIZE = 0x02000000
+    if n > MAX_SIZE:
+        raise SerializationError('Asked to read 0x%x bytes; MAX_SIZE exceeded' % n)
+    r = f.read(n)
+    if len(r) < n:
+        raise SerializationTruncationError('Asked to read %i bytes, but only got %i' % (n, len(r)))
+    return r
+
+B58_DIGITS = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
+
+class Base58Error(Exception):
+    pass
+
+class InvalidBase58Error(Base58Error):
+    """Raised on generic invalid base58 data, such as bad characters.
+    Checksum failures raise Base58ChecksumError specifically.
+    """
+    pass
+
+def b58encode(b):
+    """Encode bytes to a base58-encoded string"""
+
+    # Convert big-endian bytes to integer
+    n = int('0x0' + binascii.hexlify(b).decode('utf8'), 16)
+
+    # Divide that integer into bas58
+    res = []
+    while n > 0:
+        n, r = divmod(n, 58)
+        res.append(B58_DIGITS[r])
+    res = ''.join(res[::-1])
+
+    # Encode leading zeros as base58 zeros
+    czero = b'\x00'
+    if sys.version > '3':
+        # In Python3 indexing a bytes returns numbers, not characters.
+        czero = 0
+    pad = 0
+    for c in b:
+        if c == czero:
+            pad += 1
         else:
-            raise ValueError("Invalid base!")
-
-    def changebase(string, frm, to, minlen=0):
-        if frm == to:
-            return lpad(string, get_code_string(frm)[0], minlen)
-        return encode(decode(string, frm), to, minlen)
-
-    def bin_to_b58check(inp, magicbyte=0):
-        inp_fmtd = chr(int(magicbyte)) + inp
-        leadingzbytes = len(re.match('^\x00*', inp_fmtd).group(0))
-        checksum = bin_dbl_sha256(inp_fmtd)[:4]
-        return '1' * leadingzbytes + changebase(inp_fmtd + checksum, 256, 58)
-
-    def bytes_to_hex_string(b):
-        return b.encode('hex')
-
-    def safe_from_hex(s):
-        return s.decode('hex')
-
-    def from_int_to_byte(a):
-        return chr(a)
-
-    def from_byte_to_int(a):
-        return ord(a)
-
-    def from_string_to_bytes(a):
-        return a
-
-    def safe_hexlify(a):
-        return binascii.hexlify(a)
-
-    def encode(val, base, minlen=0):
-        base, minlen = int(base), int(minlen)
-        code_string = get_code_string(base)
-        result = ""
-        while val > 0:
-            result = code_string[val % base] + result
-            val //= base
-        return code_string[0] * max(minlen - len(result), 0) + result
-
-    def decode(string, base):
-        base = int(base)
-        code_string = get_code_string(base)
-        result = 0
-        if base == 16:
-            string = string.lower()
-        while len(string) > 0:
-            result *= base
-            result += code_string.find(string[0])
-            string = string[1:]
-        return result
-
-else:
-    raise NotImplementedError("Only Python2 currently supported by btc interface") #pragma: no cover
+            break
+    return B58_DIGITS[0] * pad + res
+
+def b58decode(s):
+    """Decode a base58-encoding string, returning bytes"""
+    if not s:
+        return b''
+
+    # Convert the string to an integer
+    n = 0
+    for c in s:
+        n *= 58
+        if c not in B58_DIGITS:
+            raise InvalidBase58Error('Character %r is not a valid base58 character' % c)
+        digit = B58_DIGITS.index(c)
+        n += digit
+
+    # Convert the integer to bytes
+    h = '%x' % n
+    if len(h) % 2:
+        h = '0' + h
+    res = bytes(binascii.unhexlify(h.encode('utf8')))
+
+    # Add padding back.
+    pad = 0
+    for c in s[:-1]:
+        if c == B58_DIGITS[0]: pad += 1
+        else: break
+    return b'\x00' * pad + res
+
+def uint256encode(s):
+    """Convert bytes to uint256"""
+    r = 0
+    t = struct.unpack(b"<IIIIIIII", s[:32])
+    for i in range(8):
+        r += t[i] << (i * 32)
+    return r
+
+def uint256decode(u):
+    r = b""
+    for i in range(8):
+        r += struct.pack(b'<I', u >> (i * 32) & 0xffffffff)
+    return r
+
+def encode(val, base, minlen=0):
+    base, minlen = int(base), int(minlen)
+    code_string = get_code_string(base)
+    result_bytes = bytes()
+    while val > 0:
+        curcode = code_string[val % base]
+        result_bytes = bytes([ord(curcode)]) + result_bytes
+        val //= base
+
+    pad_size = minlen - len(result_bytes)
+
+    padding_element = b'\x00' if base == 256 else b'1' \
+        if base == 58 else b'0'
+    if (pad_size > 0):
+        result_bytes = padding_element*pad_size + result_bytes
+
+    result_string = ''.join([chr(y) for y in result_bytes])
+    result = result_bytes if base == 256 else result_string
+
+    return result
+
+def decode(string, base):
+    if base == 256 and isinstance(string, str):
+        string = bytes(bytearray.fromhex(string))
+    base = int(base)
+    code_string = get_code_string(base)
+    result = 0
+    if base == 256:
+        def extract(d, cs):
+            if isinstance(d, int):
+                return d
+            else:
+                return struct.unpack(b'B', d)[0]
+    else:
+        def extract(d, cs):
+            return cs.find(d if isinstance(d, str) else chr(d))
+
+    if base == 16:
+        string = string.lower()
+    while len(string) > 0:
+        result *= base
+        result += extract(string[0], code_string)
+        string = string[1:]
+    return result
 
 """PoDLE related primitives
 """
@@ -98,7 +223,7 @@ def getG(compressed=True):
     """Returns the public key binary
     representation of secp256k1 G
     """
-    priv = "\x00"*31 + "\x01"
+    priv = b"\x00"*31 + b"\x01"
     G = secp256k1.PrivateKey(priv).public_key.format(compressed)
     return G
 
@@ -137,12 +262,11 @@ def bin_sha256(string):
 def sha256(string):
     return bytes_to_hex_string(bin_sha256(string))
 
-def bin_dbl_sha256(s):
-    bytes_to_hash = from_string_to_bytes(s)
+def bin_dbl_sha256(bytes_to_hash):
     return hashlib.sha256(hashlib.sha256(bytes_to_hash).digest()).digest()
 
 def dbl_sha256(string):
-    return safe_hexlify(bin_dbl_sha256(string))
+    return hashlib.sha256(hashlib.sha256(string).digest()).hexdigest()
 
 def hash_to_int(x):
     if len(x) in [40, 64]:
@@ -150,11 +274,14 @@ def hash_to_int(x):
     return decode(x, 256)
 
 def num_to_var_int(x):
-    x = int(x)
+    if not isinstance(x, int):
+        if len(x) == 0:
+            return b'\x00'
+        x = struct.unpack(b'B', x)[0]
     if x < 253: return from_int_to_byte(x)
-    elif x < 65536: return from_int_to_byte(253) + encode(x, 256, 2)[::-1]
-    elif x < 4294967296: return from_int_to_byte(254) + encode(x, 256, 4)[::-1]
-    else: return from_int_to_byte(255) + encode(x, 256, 8)[::-1]
+    elif x < 65536: return from_int_to_byte(253) + struct.pack(b'<H', x)
+    elif x < 4294967296: return from_int_to_byte(254) + struct.pack(b'<I', x)
+    else: return from_int_to_byte(255) + struct.pack(b'<Q', x)
 
 def message_sig_hash(message):
     """Used for construction of signatures of
@@ -166,22 +293,20 @@ def message_sig_hash(message):
 
 # Encodings
 def b58check_to_bin(inp):
-    leadingzbytes = len(re.match('^1*', inp).group(0))
-    data = b'\x00' * leadingzbytes + changebase(inp, 58, 256)
+    data = b58decode(inp)
     assert bin_dbl_sha256(data[:-4])[:4] == data[-4:]
     return data[1:-4]
 
 def get_version_byte(inp):
-    leadingzbytes = len(re.match('^1*', inp).group(0))
-    data = b'\x00' * leadingzbytes + changebase(inp, 58, 256)
+    data = b58decode(inp)
     assert bin_dbl_sha256(data[:-4])[:4] == data[-4:]
-    return ord(data[0])
+    return data[:1]
 
-def hex_to_b58check(inp, magicbyte=0):
+def hex_to_b58check(inp, magicbyte=b'\x00'):
     return bin_to_b58check(binascii.unhexlify(inp), magicbyte)
 
 def b58check_to_hex(inp):
-    return safe_hexlify(b58check_to_bin(inp))
+    return binascii.hexlify(b58check_to_bin(inp))
 
 def pubkey_to_address(pubkey, magicbyte=0):
     if len(pubkey) in [66, 130]:
@@ -191,9 +316,11 @@ def pubkey_to_address(pubkey, magicbyte=0):
 
 pubtoaddr = pubkey_to_address
 
-def wif_compressed_privkey(priv, vbyte=0):
+def wif_compressed_privkey(priv, vbyte=b'\x00'):
     """Convert privkey in hex compressed to WIF compressed
     """
+    if not isinstance(vbyte, int):
+        vbyte = struct.unpack(b'B', vbyte)[0]
     if len(priv) != 66:
         raise Exception("Wrong length of compressed private key")
     if priv[-2:] != '01':
@@ -201,20 +328,22 @@ def wif_compressed_privkey(priv, vbyte=0):
     return bin_to_b58check(binascii.unhexlify(priv), 128 + int(vbyte))
 
 
-def from_wif_privkey(wif_priv, compressed=True, vbyte=0):
+def from_wif_privkey(wif_priv, compressed=True, vbyte=b'\x00'):
     """Convert WIF compressed privkey to hex compressed.
     Caller specifies the network version byte (0 for mainnet, 0x6f
     for testnet) that the key should correspond to; if there is
     a mismatch an error is thrown. WIF encoding uses 128+ this number.
     """
+    if isinstance(vbyte, int):
+        vbyte = struct.pack(b'B', vbyte)
     bin_key = b58check_to_bin(wif_priv)
     claimed_version_byte = get_version_byte(wif_priv)
-    if not 128+vbyte == claimed_version_byte:
+    if not from_int_to_byte(128+from_byte_to_int(vbyte)) == claimed_version_byte:
         raise Exception(
             "WIF key version byte is wrong network (mainnet/testnet?)")
     if compressed and not len(bin_key) == 33:
         raise Exception("Compressed private key is not 33 bytes")
-    if compressed and not bin_key[-1] == '\x01':
+    if compressed and not bin_key[-1:] == b'\x01':
         raise Exception("Private key has incorrect compression byte")
     return safe_hexlify(bin_key)
 
@@ -252,9 +381,9 @@ def hexbin(func):
             newargs = []
             for arg in args[:-1]:
                 if isinstance(arg, (list, tuple)):
-                    newargs += [[x.decode('hex') for x in arg]]
+                    newargs += [[binascii.unhexlify(x) for x in arg]]
                 else:
-                    newargs += [arg.decode('hex')]
+                    newargs += [binascii.unhexlify(arg)]
             newargs += [False]
             returnval = func(*newargs, **kwargs)
             if isinstance(returnval, bool):
@@ -268,7 +397,7 @@ def hexbin(func):
 
 def read_privkey(priv):
     if len(priv) == 33:
-        if priv[-1] == '\x01':
+        if priv[-1:] == b'\x01':
             compressed = True
         else:
             raise Exception("Invalid private key")
@@ -286,7 +415,7 @@ def privkey_to_pubkey_inner(priv, usehex):
     and return compressed/uncompressed public key as appropriate.'''
     compressed, priv = read_privkey(priv)
     #secp256k1 checks for validity of key value.
-    newpriv = secp256k1.PrivateKey(secret=priv)
+    newpriv = secp256k1.PrivateKey(secret=bytes_to_native_str(priv))
     return newpriv.public_key.format(compressed)
 
 def privkey_to_pubkey(priv, usehex=True):
@@ -311,7 +440,7 @@ def multiply(s, pub, usehex, rawpub=True, return_serialized=True):
     '''
     newpub = secp256k1.PublicKey(pub)
     #see note to "tweak_mul" function in podle.py
-    res = newpub.multiply(s)
+    res = newpub.multiply(bytes_to_native_str(s))
     if not return_serialized:
         return res
     return res.format()
@@ -339,7 +468,7 @@ def add_privkeys(priv1, priv2, usehex):
     p1 = secp256k1.PrivateKey(newpriv1)
     res = p1.add(newpriv2).secret
     if compressed:
-        res += '\x01'
+        res += b'\x01'
     return res
 
 @hexbin
diff --git a/jmbitcoin/jmbitcoin/secp256k1_transaction.py b/jmbitcoin/jmbitcoin/secp256k1_transaction.py
index 54f0d62..e9d0aff 100644
--- a/jmbitcoin/jmbitcoin/secp256k1_transaction.py
+++ b/jmbitcoin/jmbitcoin/secp256k1_transaction.py
@@ -1,87 +1,61 @@
 #!/usr/bin/python
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import *
+from past.builtins import basestring
+from io import BytesIO
 import binascii
 import copy
 import re
-import sys
+import os
 from jmbitcoin.secp256k1_main import *
 from jmbitcoin.bech32 import *
-from _functools import reduce
 
-is_python2 = sys.version_info.major == 2
-
-### Hex to bin converter and vice versa for objects
-def json_is_base(obj, base):
-    if not is_python2 and isinstance(obj, bytes): #pragma: no cover
-        return False
+# Transaction serialization and deserialization
 
-    alpha = get_code_string(base)
-    if isinstance(obj, string_types):
-        for i in range(len(obj)):
-            if alpha.find(obj[i]) == -1:
-                return False
-        return True
-    elif isinstance(obj, int_types) or obj is None:
-        return True
-    elif isinstance(obj, list):
-        for i in range(len(obj)):
-            if not json_is_base(obj[i], base):
-                return False
-        return True
+def deserialize(txinp):
+    if isinstance(txinp, basestring) and re.match('^[0-9a-fA-F]*$', txinp):
+        tx = BytesIO(binascii.unhexlify(txinp))
+        hexout = True
     else:
-        for x in obj:
-            if not json_is_base(obj[x], base):
-                return False
-        return True
-
+        tx = BytesIO(txinp)
+        hexout = False
 
-def json_changebase(obj, changer):
-    if isinstance(obj, string_or_bytes_types):
-        return changer(obj)
-    elif isinstance(obj, int_types) or obj is None:
-        return obj
-    elif isinstance(obj, list):
-        return [json_changebase(x, changer) for x in obj]
-    return dict((x, json_changebase(obj[x], changer)) for x in obj)
-
-# Transaction serialization and deserialization
+    def hex_string(scriptbytes, hexout):
+        if hexout:
+            return binascii.hexlify(scriptbytes)
+        else:
+            return scriptbytes
 
-def deserialize(tx):
-    if isinstance(tx, (str, unicode)) and re.match('^[0-9a-fA-F]*$', tx):
-        #tx = bytes(bytearray.fromhex(tx))
-        return json_changebase(
-            deserialize(binascii.unhexlify(tx)), lambda x: safe_hexlify(x))
-    # http://stackoverflow.com/questions/4851463/python-closure-write-to-variable-in-parent-scope
-    # Python's scoping rules are demented, requiring me to make pos an object
-    # so that it is call-by-reference
-    pos = [0]
-
-    #TODO: these are disgustingly ignorant of overrun errors!
     def read_as_int(bytez):
-        pos[0] += bytez
-        return decode(tx[pos[0] - bytez:pos[0]][::-1], 256)
+        if bytez == 2:
+            return struct.unpack(b'<H', ser_read(tx, 2))[0]
+        elif bytez == 4:
+            return struct.unpack(b'<I', ser_read(tx, 4))[0]
+        elif bytez == 1:
+            return struct.unpack(b'B', ser_read(tx, 1))[0]
+        elif bytez == 8:
+            return struct.unpack(b'<Q', ser_read(tx, 8))[0]
+        else:
+            raise SerializationError('Asked to read unsupported %x bytes; bytez can only be 1, 2, 4 or 8' % bytez)
 
     def read_var_int():
-        pos[0] += 1
-
-        val = from_byte_to_int(tx[pos[0] - 1])
+        val = from_byte_to_int(ser_read(tx, 1))
         if val < 253:
             return val
         return read_as_int(pow(2, val - 252))
 
-    def read_bytes(bytez):
-        pos[0] += bytez
-        return tx[pos[0] - bytez:pos[0]]
-
     def read_var_string():
         size = read_var_int()
-        return read_bytes(size)
+        return ser_read(tx, size)
 
     def read_flag_byte(val):
-        flag = read_bytes(1)
+        last = tx.tell()
+        flag = ser_read(tx, 1)
         if from_byte_to_int(flag)==val:
             return True
         else:
-            pos[0] -= 1
+            tx.seek(last)
             return False
 
     obj = {"ins": [], "outs": []}
@@ -98,18 +72,18 @@ def deserialize(tx):
     for i in range(ins):
         obj["ins"].append({
             "outpoint": {
-                "hash": read_bytes(32)[::-1],
+                "hash": hex_string(ser_read(tx, 32)[::-1], hexout),
                 "index": read_as_int(4)
             },
             #TODO this will probably crap out on null for segwit
-            "script": read_var_string(),
+            "script": hex_string(read_var_string(), hexout),
             "sequence": read_as_int(4)
         })
     outs = read_var_int()
     for i in range(outs):
         obj["outs"].append({
             "value": read_as_int(8),
-            "script": read_var_string()
+            "script": hex_string(read_var_string(), hexout)
         })
     #segwit flag is only set if at least one txinwitness exists,
     #in other words it would have to be at least partially signed;
@@ -127,52 +101,98 @@ def deserialize(tx):
             num_items = read_var_int()
             items = []
             for ni in range(num_items):
-                items.append(read_var_string())
+                items.append(hex_string(read_var_string(), hexout))
             obj["ins"][i]["txinwitness"] = items
 
     obj["locktime"] = read_as_int(4)
     return obj
 
-def serialize(txobj):
-    o = []
-    if json_is_base(txobj, 16):
-        json_changedbase = json_changebase(txobj,
-                                           lambda x: binascii.unhexlify(x))
-        hexlified = safe_hexlify(serialize(json_changedbase))
-        return hexlified
-    o.append(encode(txobj["version"], 256, 4)[::-1])
+def serialize(tx):
+    """Assumes a deserialized transaction in which all
+    dictionary values are decoded hex strings or numbers.
+    Rationale: mixing raw bytes/hex/strings in dict objects causes
+    complexity; since the dict tx object has to be inspected
+    in this function, avoid complicated logic elsewhere by making
+    all conversions to raw byte strings happen here.
+    Table of dictionary keys and type for the value:
+    ================================================
+    version: int
+    ins: list
+    ins[0]["outpoint"]["hash"]: hex encoded string
+    ins[0]["outpoint"]["index"]: int
+    ins[0]["script"]: hex encoded string
+    ins[0]["sequence"]: int
+    ins[0]["txinwitness"]: list (optional, may not exist)
+    ins[0]["txinwitness"][0]: hex encoded string
+    outs: list
+    outs[0]["script"]: hex encoded string
+    outs[0]["value"]: int
+    locktime: int
+    =================================================
+    Returned serialized transaction is a byte string.
+    """
+    #Because we are manipulating the dict in-place, need
+    #to work on a copy
+    txobj = copy.deepcopy(tx)
+    o = BytesIO()
+    hexout = False
+    o.write(struct.pack(b'<I', txobj["version"]))
     segwit = False
-    if any("txinwitness" in x.keys() for x in txobj["ins"]):
+    if any("txinwitness" in x for x in txobj["ins"]):
         segwit = True
     if segwit:
         #append marker and flag
-        o.append('\x00')
-        o.append('\x01')
-    o.append(num_to_var_int(len(txobj["ins"])))
+        o.write(b'\x00')
+        o.write(b'\x01')
+    o.write(num_to_var_int(len(txobj["ins"])))
     for inp in txobj["ins"]:
-        o.append(inp["outpoint"]["hash"][::-1])
-        o.append(encode(inp["outpoint"]["index"], 256, 4)[::-1])
-        o.append(num_to_var_int(len(inp["script"])) + (inp["script"] if inp[
-            "script"] or is_python2 else bytes()))
-        o.append(encode(inp["sequence"], 256, 4)[::-1])
-    o.append(num_to_var_int(len(txobj["outs"])))
+        if len(inp["outpoint"]["hash"]) == 64:
+            o.write(binascii.unhexlify(inp["outpoint"]["hash"])[::-1])
+            hexout = True
+        elif len(inp["outpoint"]["hash"]) == 32:
+            o.write(inp["outpoint"]["hash"][::-1])
+        else:
+            raise SerializationError('Hash has unsupported length: %x bytes; must be 64 or 32 bytes' % len(inp["outpoint"]["hash"]))
+        o.write(struct.pack(b'<I', inp["outpoint"]["index"]))
+        if len(inp["script"]) == 0:
+            o.write(b'\x00')
+        elif isinstance(inp["script"], basestring) and re.match('^[0-9a-fA-F]*$', inp["script"]):
+            o.write(num_to_var_int(len(binascii.unhexlify(inp["script"]))))
+            o.write(binascii.unhexlify(inp["script"]))
+        else:
+            o.write(num_to_var_int(len(inp["script"])))
+            o.write(inp["script"])
+        o.write(struct.pack(b'<I', inp["sequence"]))
+    o.write(num_to_var_int(len(txobj["outs"])))
     for out in txobj["outs"]:
-        o.append(encode(out["value"], 256, 8)[::-1])
-        o.append(num_to_var_int(len(out["script"])) + out["script"])
+        o.write(struct.pack(b'<Q', out["value"]))
+        if len(out["script"]) == 0:
+            o.write(b'\x00')
+        elif isinstance(out["script"], basestring) and re.match('^[0-9a-fA-F]*$', out["script"]):
+            o.write(num_to_var_int(len(binascii.unhexlify(out["script"]))))
+            o.write(binascii.unhexlify(out["script"]))
+        else:
+            o.write(num_to_var_int(len(out["script"])))
+            o.write(out["script"])
     if segwit:
         #number of witnesses is not explicitly encoded;
         #it's implied by txin length
         for inp in txobj["ins"]:
-            if "txinwitness" not in inp.keys():
-                o.append('\x00')
+            if "txinwitness" not in inp:
+                o.write(b'\x00')
                 continue
             items = inp["txinwitness"]
-            o.append(num_to_var_int(len(items)))
+            o.write(num_to_var_int(len(items)))
             for item in items:
-                o.append(num_to_var_int(len(item)) + item)
-    o.append(encode(txobj["locktime"], 256, 4)[::-1])
+                if isinstance(item, basestring) and re.match('^[0-9a-fA-F]*$', item):
+                    item = binascii.unhexlify(item)
+                o.write(num_to_var_int(len(item)) + item)
+    o.write(struct.pack(b'<I', txobj["locktime"]))
 
-    return ''.join(o) if is_python2 else reduce(lambda x, y: x + y, o, bytes())
+    if hexout:
+        return binascii.hexlify(o.getvalue())
+    else:
+        return o.getvalue()
 
 # Hashing transactions for signing
 
@@ -192,54 +212,61 @@ def segwit_signature_form(txobj, i, script, amount, hashcode=SIGHASH_ALL,
     #    return serialize(segwit_signature_form(deserialize(txobj), i, script,
     #                                           amount, hashcode))
     script = decoder_func(script)
-    nVersion = encode(txobj["version"], 256, 4)[::-1]
+    nVersion = struct.pack(b'<I', txobj["version"])
+    if not isinstance(hashcode, int):
+        hashcode = struct.unpack(b'B', hashcode)[0]
     #create hashPrevouts
     if hashcode & SIGHASH_ANYONECANPAY:
-        hashPrevouts = "\x00"*32
+        hashPrevouts = b"\x00"*32
     else:
-        pi = ""
+        pi = b""
         for inp in txobj["ins"]:
             pi += decoder_func(inp["outpoint"]["hash"])[::-1]
-            pi += encode(inp["outpoint"]["index"], 256, 4)[::-1]
+            pi += struct.pack(b'<I', inp["outpoint"]["index"])
         hashPrevouts = bin_dbl_sha256(pi)
     #create hashSequence
     if not hashcode & SIGHASH_ANYONECANPAY and not (
         hashcode & 0x1f == SIGHASH_SINGLE) and not (hashcode & 0x1f == SIGHASH_NONE):
-        pi = ""
+        pi = b""
         for inp in txobj["ins"]:
-            pi += encode(inp["sequence"], 256, 4)[::-1]
+            pi += struct.pack(b'<I', inp["sequence"])
         hashSequence = bin_dbl_sha256(pi)
     else:
-        hashSequence = "\x00"*32
+        hashSequence = b"\x00"*32
     #add this input's outpoint
     thisOut = decoder_func(txobj["ins"][i]["outpoint"]["hash"])[::-1]
-    thisOut += encode(txobj["ins"][i]["outpoint"]["index"], 256, 4)[::-1]
+    thisOut += struct.pack(b'<I', txobj["ins"][i]["outpoint"]["index"])
     scriptCode = num_to_var_int(len(script)) + script
-    amt = encode(amount, 256, 8)[::-1]
-    thisSeq = encode(txobj["ins"][i]["sequence"], 256, 4)[::-1]
+    amt = struct.pack(b'<Q', amount)
+    thisSeq = struct.pack(b'<I', txobj["ins"][i]["sequence"])
     #create hashOutputs
     if not (hashcode & 0x1f == SIGHASH_SINGLE) and not (hashcode & 0x1f == SIGHASH_NONE):
-        pi = ""
+        pi = b""
         for out in txobj["outs"]:
-            pi += encode(out["value"], 256, 8)[::-1]
+            pi += struct.pack(b'<Q', out["value"])
             pi += (num_to_var_int(len(decoder_func(out["script"]))) + \
                    decoder_func(out["script"]))
         hashOutputs = bin_dbl_sha256(pi)
     elif hashcode & 0x1f == SIGHASH_SINGLE and i < len(txobj['outs']):
-        pi = encode(txobj["outs"][i]["value"], 256, 8)[::-1]
+        pi = struct.pack(b'<Q', txobj["outs"][i]["value"])
         pi += (num_to_var_int(len(decoder_func(txobj["outs"][i]["script"]))) +
                decoder_func(txobj["outs"][i]["script"]))
         hashOutputs = bin_dbl_sha256(pi)
     else:
-        hashOutputs = "\x00"*32
-    nLockTime = encode(txobj["locktime"], 256, 4)[::-1]
+        hashOutputs = b"\x00"*32
+    nLockTime = struct.pack(b'<I', txobj["locktime"])
     return nVersion + hashPrevouts + hashSequence + thisOut + scriptCode + amt + \
            thisSeq + hashOutputs + nLockTime
 
 def signature_form(tx, i, script, hashcode=SIGHASH_ALL):
-    i, hashcode = int(i), int(hashcode)
-    if isinstance(tx, string_or_bytes_types):
-        return serialize(signature_form(deserialize(tx), i, script, hashcode))
+    if not isinstance(hashcode, int):
+        hashcode = struct.unpack(b'B', hashcode)[0]
+    if isinstance(tx, basestring) and re.match('^[0-9a-fA-F]*$', tx):
+        tx = deserialize(tx)
+    elif isinstance(tx, basestring):
+        tx = deserialize(binascii.hexlify(tx))
+    if isinstance(script, basestring) and not re.match('^[0-9a-fA-F]*$', script):
+        script = binascii.hexlify(script)
     newtx = copy.deepcopy(tx)
     for inp in newtx["ins"]:
         #If tx is passed in in segwit form, it must be switched to non-segwit.
@@ -288,16 +315,19 @@ def txhash(tx, hashcode=None, check_sw=True):
     If check_sw is True it checks the serialized format for
     segwit flag bytes, and produces the correct form for txid (not wtxid).
     """
-    if isinstance(tx, str) and re.match('^[0-9a-fA-F]*$', tx):
-        tx = changebase(tx, 16, 256)
+    if not isinstance(tx, basestring):
+        tx = serialize(tx)
+    if isinstance(tx, basestring) and re.match('^[0-9a-fA-F]*$', tx):
+        tx = binascii.unhexlify(tx)
     if check_sw and from_byte_to_int(tx[4]) == 0:
         if not from_byte_to_int(tx[5]) == 1:
             #This invalid, but a raise is a DOS vector in some contexts.
             return None
         return segwit_txid(tx, hashcode)
     if hashcode:
-        return dbl_sha256(from_string_to_bytes(tx) + encode(
-            int(hashcode), 256, 4)[::-1])
+        if not isinstance(hashcode, int):
+            hashcode = struct.unpack(b'B', hashcode)[0]
+        return dbl_sha256(from_string_to_bytes(tx) + struct.pack(b'<I', hashcode))
     else:
         return safe_hexlify(bin_dbl_sha256(tx)[::-1])
 
@@ -337,12 +367,7 @@ def mk_scripthash_script(addr):
 
 def segwit_scriptpubkey(witver, witprog):
     """Construct a Segwit scriptPubKey for a given witness program."""
-    if sys.version_info >= (3, 0):
-        x = bytes([witver + 0x50 if witver else 0, len(witprog)] + witprog)
-    else:
-        x = chr(witver + 0x50) if witver else '\x00'
-        x += chr(len(witprog))
-        x += bytearray(witprog)
+    x = bytes([witver + 0x50 if witver else 0, len(witprog)] + witprog)
     return x
 
 def mk_native_segwit_script(addr):
@@ -412,31 +437,53 @@ def p2sh_scriptaddr(script, magicbyte=5):
 scriptaddr = p2sh_scriptaddr
 
 
-def deserialize_script(script):
-    if isinstance(script, str) and re.match('^[0-9a-fA-F]*$', script):
-        return json_changebase(
-            deserialize_script(binascii.unhexlify(script)),
-            lambda x: safe_hexlify(x))
-    out, pos = [], 0
-    while pos < len(script):
-        code = from_byte_to_int(script[pos])
+def deserialize_script(scriptinp):
+    """Note that this is not used internally, in
+    the jmbitcoin package, to deserialize() transactions;
+    its function is only to allow parsing of scripts by
+    external callers. Thus, it returns in the format used
+    outside the package: a deserialized script is a list of
+    entries which can be any of:
+    None
+    integer
+    hex string
+    """
+    def hex_string(scriptbytes, hexout):
+        if hexout:
+            return binascii.hexlify(scriptbytes)
+        else:
+            return scriptbytes
+
+    if isinstance(scriptinp, basestring) and re.match('^[0-9a-fA-F]*$', scriptinp):
+        script = BytesIO(binascii.unhexlify(scriptinp))
+        hexout = True
+    else:
+        script = BytesIO(scriptinp)
+        hexout = False
+    script.seek(0, os.SEEK_END)
+    length = script.tell()
+    script.seek(0, os.SEEK_SET)
+    out = []
+    while script.tell() < length:
+        code = from_byte_to_int(ser_read(script, 1))
         if code == 0:
             out.append(None)
-            pos += 1
         elif code <= 75:
-            out.append(script[pos + 1:pos + 1 + code])
-            pos += 1 + code
+            out.append(hex_string(ser_read(script, code), hexout))
         elif code <= 78:
-            szsz = pow(2, code - 76)
-            sz = decode(script[pos + szsz:pos:-1], 256)
-            out.append(script[pos + 1 + szsz:pos + 1 + szsz + sz])
-            pos += 1 + szsz + sz
+            if code == 78:
+                sz = struct.unpack(b'<I', ser_read(script, 4))[0]
+            elif code == 77:
+                sz = struct.unpack(b'<H', ser_read(script, 2))[0]
+            elif code == 76:
+                sz = struct.unpack(b'<B', ser_read(script, 1))[0]
+            else:
+                sz = code
+            out.append(hex_string(ser_read(script, sz), hexout))
         elif code <= 96:
             out.append(code - 80)
-            pos += 1
         else:
             out.append(code)
-            pos += 1
     return out
 
 
@@ -449,45 +496,28 @@ def serialize_script_unit(unit):
     elif unit is None:
         return b'\x00'
     else:
+        if isinstance(unit, basestring) and re.match('^[0-9a-fA-F]*$', unit):
+            unit = binascii.unhexlify(unit)
         if len(unit) <= 75:
             return from_int_to_byte(len(unit)) + unit
         elif len(unit) < 256:
-            return from_int_to_byte(76) + from_int_to_byte(len(unit)) + unit
+            return from_int_to_byte(76) + struct.pack(b'<B', len(unit)) + unit
         elif len(unit) < 65536:
-            return from_int_to_byte(77) + encode(len(unit), 256, 2)[::-1] + unit
+            return from_int_to_byte(77) + struct.pack(b'<H', len(unit)) + unit
         else:
-            return from_int_to_byte(78) + encode(len(unit), 256, 4)[::-1] + unit
-
-
-if is_python2:
-
-    def serialize_script(script):
-        #bugfix: if *every* item in the script is of type int,
-        #for example a script of OP_TRUE, or None,
-        #then the previous version would always report json_is_base as True,
-        #resulting in an infinite loop (look who's demented now).
-        #There is no easy solution without being less flexible;
-        #here we default to returning a hex serialization in cases where
-        #there are no strings to use as flags.
-        if all([(isinstance(x, int) or x is None) for x in script]):
-            #no indication given whether output should be hex or binary, so..?
-            return binascii.hexlify(''.join(map(serialize_script_unit, script)))
-        if json_is_base(script, 16):
-            return binascii.hexlify(serialize_script(json_changebase(
-                script, lambda x: binascii.unhexlify(x))))
-        return ''.join(map(serialize_script_unit, script))
-
-else: #pragma: no cover
-
-    def serialize_script(script):
-        #TODO Python 3 bugfix as above needed
-        if json_is_base(script, 16):
-            return safe_hexlify(serialize_script(json_changebase(
-                script, lambda x: binascii.unhexlify(x))))
-
-        result = bytes()
-        for b in map(serialize_script_unit, script):
-            result += b if isinstance(b, bytes) else bytes(b, 'utf-8')
+            return from_int_to_byte(78) + struct.pack(b'<I', len(unit)) + unit
+
+
+def serialize_script(script):
+    result = b''
+    hexout = True
+    for b in script:
+        if isinstance(b, basestring) and not re.match('^[0-9a-fA-F]*$', b):
+            hexout = False
+        result += serialize_script_unit(b)
+    if hexout:
+        return binascii.hexlify(result)
+    else:
         return result
 
 
@@ -508,18 +538,18 @@ def verify_tx_input(tx, i, script, sig, pub, witness=None, amount=None):
     if re.match('^[0-9a-fA-F]*$', script):
         script = binascii.unhexlify(script)
     if not re.match('^[0-9a-fA-F]*$', sig):
-        sig = safe_hexlify(sig)
+        sig = binascii.hexlify(sig)
     if not re.match('^[0-9a-fA-F]*$', pub):
-        pub = safe_hexlify(pub)
+        pub = binascii.hexlify(pub)
     if witness:
         if not re.match('^[0-9a-fA-F]*$', witness):
             witness = safe_hexlify(witness)
-    hashcode = decode(sig[-2:], 16)
+    hashcode = binascii.unhexlify(sig[-2:])
     if witness and amount:
         #TODO assumes p2sh wrapped segwit input; OK for JM wallets
-        scriptCode = "76a914"+hash160(binascii.unhexlify(pub))+"88ac"
-        modtx = segwit_signature_form(deserialize(binascii.hexlify(tx)), int(i),
-                                      scriptCode, amount, hashcode)
+        scriptCode = binascii.unhexlify("76a914"+hash160(binascii.unhexlify(pub))+"88ac")
+        modtx = segwit_signature_form(deserialize(tx), int(i),
+                                      scriptCode, amount, hashcode, decoder_func=lambda x: x)
     else:
         modtx = signature_form(tx, int(i), script, hashcode)
     return ecdsa_tx_verify(modtx, sig, pub, hashcode)
@@ -527,9 +557,11 @@ def verify_tx_input(tx, i, script, sig, pub, witness=None, amount=None):
 
 def sign(tx, i, priv, hashcode=SIGHASH_ALL, usenonce=None, amount=None):
     i = int(i)
-    if (not is_python2 and isinstance(re, bytes)) or not re.match(
-            '^[0-9a-fA-F]*$', tx):
-        return binascii.unhexlify(sign(safe_hexlify(tx), i, priv))
+    if isinstance(tx, basestring) and re.match('^[0-9a-fA-F]*$', tx):
+        tx = binascii.unhexlify(tx)
+        hexout = True
+    else:
+        hexout = False
     if len(priv) <= 33:
         priv = safe_hexlify(priv)
     if amount:
@@ -541,7 +573,13 @@ def sign(tx, i, priv, hashcode=SIGHASH_ALL, usenonce=None, amount=None):
     sig = ecdsa_tx_sign(signing_tx, priv, hashcode, usenonce=usenonce)
     txobj = deserialize(tx)
     txobj["ins"][i]["script"] = serialize_script([sig, pub])
-    return serialize(txobj)
+    serobj = serialize(txobj)
+    if hexout and isinstance(serobj, basestring) and not re.match('^[0-9a-fA-F]*$', serobj):
+        return binascii.hexlify(serobj)
+    elif not hexout and re.match('^[0-9a-fA-F]*$', serobj):
+        return binascii.unhexlify(serobj)
+    else:
+        return serobj
 
 def p2sh_p2wpkh_sign(tx, i, priv, amount, hashcode=SIGHASH_ALL, usenonce=None):
     """Given a serialized transaction, index, private key in hex,
@@ -612,7 +650,6 @@ def mktx(*args):
                 (ins if is_inp(a) else outs).append(a)
         else:
             (ins if is_inp(arg) else outs).append(arg)
-
     txobj = {"locktime": 0, "version": 1, "ins": [], "outs": []}
     for i in ins:
         if isinstance(i, dict) and "outpoint" in i:
@@ -627,7 +664,7 @@ def mktx(*args):
                 "sequence": 4294967295
             })
     for o in outs:
-        if isinstance(o, string_or_bytes_types):
+        if isinstance(o, basestring):
             addr = o[:o.find(':')]
             val = int(o[o.find(':') + 1:])
             o = {}
@@ -646,6 +683,5 @@ def mktx(*args):
             raise Exception("Could not find 'address' or 'script' in output.")
         outobj["value"] = o["value"]
         txobj["outs"].append(outobj)
-
     return serialize(txobj)
 
diff --git a/jmbitcoin/test/test_addresses.py b/jmbitcoin/test/test_addresses.py
index 0888374..810f464 100644
--- a/jmbitcoin/test/test_addresses.py
+++ b/jmbitcoin/test/test_addresses.py
@@ -1,3 +1,6 @@
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 import jmbitcoin as btc
 import json
 import pytest
@@ -7,14 +10,13 @@ testdir = os.path.dirname(os.path.realpath(__file__))
 def validate_address(addr, nettype):
     """A mock of jmclient.validate_address
     """
-    BTC_P2PK_VBYTE = {"mainnet": 0x00, "testnet": 0x6f}
-    BTC_P2SH_VBYTE = {"mainnet": 0x05, "testnet": 0xc4}    
+    BTC_P2PK_VBYTE = {"mainnet": b'\x00', "testnet": b'\x6f'}
+    BTC_P2SH_VBYTE = {"mainnet": b'\x05', "testnet": b'\xc4'}    
     try:
         ver = btc.get_version_byte(addr)
-    except AssertionError:
+    except AssertionError as e:
         return False, 'Checksum wrong. Typo in address?'
     except Exception as e:
-        print repr(e)
         return False, "Invalid bitcoin address"
     if ver not in [BTC_P2PK_VBYTE[nettype], BTC_P2SH_VBYTE[nettype]]:
         return False, 'Wrong address version. Testnet/mainnet confused?'
@@ -52,7 +54,6 @@ def test_b58_valid_addresses():
             else:
                 net = "mainnet"
             #if using pytest -s ; sanity check to see what's actually being tested
-            print 'testing this address: ' + addr
             res, message = validate_address(addr, net)
             assert res == True, "Incorrectly failed to validate address: " + addr + " with message: " + message
 
diff --git a/jmbitcoin/test/test_bech32.py b/jmbitcoin/test/test_bech32.py
index a04a863..a0d0d51 100644
--- a/jmbitcoin/test/test_bech32.py
+++ b/jmbitcoin/test/test_bech32.py
@@ -1,5 +1,7 @@
 #!/usr/bin/python
-from __future__ import print_function
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 
 # Copyright (c) 2017 Pieter Wuille
 #
@@ -24,21 +26,10 @@ from __future__ import print_function
 
 """Reference tests for segwit adresses"""
 
-import sys
 import binascii
 import unittest
 import jmbitcoin as btc
 
-def segwit_scriptpubkey(witver, witprog):
-    """Construct a Segwit scriptPubKey for a given witness program."""
-    if sys.version_info >= (3, 0):
-        x = bytes([witver + 0x50 if witver else 0, len(witprog)] + witprog)
-    else:
-        x = chr(witver + 0x50) if witver else '\x00'
-        x += chr(len(witprog))
-        x += bytearray(witprog)
-    return x
-
 VALID_CHECKSUM = [
     "A12UEL5L",
     "an83characterlonghumanreadablepartthatcontainsthenumber1andtheexcludedcharactersbio1tt5tgs",
@@ -120,7 +111,7 @@ class TestSegwitAddress(unittest.TestCase):
                 hrp = "tb"
                 witver, witprog = btc.bech32addr_decode(hrp, address)
             self.assertIsNotNone(witver)
-            scriptpubkey = segwit_scriptpubkey(witver, witprog)
+            scriptpubkey = btc.segwit_scriptpubkey(witver, witprog)
             self.assertEqual(scriptpubkey, binascii.unhexlify(hexscript))
             addr = btc.bech32addr_encode(hrp, witver, witprog)
             self.assertEqual(address.lower(), addr)
diff --git a/jmbitcoin/test/test_bip32.py b/jmbitcoin/test/test_bip32.py
index dc92dcb..d26c07b 100644
--- a/jmbitcoin/test/test_bip32.py
+++ b/jmbitcoin/test/test_bip32.py
@@ -1,3 +1,6 @@
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 import pytest
 import jmbitcoin as btc
 import binascii
@@ -71,13 +74,13 @@ def test_bip32_vector(vector):
     currentkey = master
     for i in range(1, len(vector['depths'])):
         currentkey = btc.bip32_ckd(currentkey, vector['depths'][i])
-        print currentkey
-        print vector['keys'][i][0]
+        print(currentkey)
+        print(vector['keys'][i][0])
         assert currentkey == vector['keys'][i][
             0], 'failed: child priv key, should be: ' + vector['keys'][i][0]
         pub = btc.bip32_privtopub(currentkey)
-        print pub
-        print vector['keys'][i][1]
+        print(pub)
+        print(vector['keys'][i][1])
         assert pub == vector['keys'][i][
             1], 'failed: child pub key, should be: ' + vector['keys'][i][1]
 
@@ -95,13 +98,13 @@ def test_ckd_pubkeys():
     pub = 'xpub68Gmy5EdvgibQVfPdqkBBCHxA5htiqg55crXYuXoQRKfDBFA1WEjWgP6LHhwBZeNK1VTsfTFUHCdrfp1bgwQ9xv5ski8PX9rL2dZXvgGDnw'
     new_pub = btc.bip32_ckd(pub, 4)
     #how to check it's right?
-    print new_pub
+    print(new_pub)
     #try to do on hardened, should fail, that's the idea:
     with pytest.raises(Exception) as e_info:
         new_pub = btc.bip32_ckd(pub, 2**31+1)
 
 def test_bip32_descend():
-    master = btc.bip32_master_key('\x07'*32)
+    master = btc.bip32_master_key(b'\x07'*32)
     end_key = btc.bip32_descend(master, [2, 3, 10000])
     assert end_key=="6856ef965940a1a7b1311dc041050ac0013e326c7ff4e2c677a7694b4f0405c901"
     end_key = btc.bip32_descend(master, 2, 5, 4, 5)
diff --git a/jmbitcoin/test/test_btc_formatting.py b/jmbitcoin/test/test_btc_formatting.py
index 53691e0..cc15276 100644
--- a/jmbitcoin/test/test_btc_formatting.py
+++ b/jmbitcoin/test/test_btc_formatting.py
@@ -1,5 +1,7 @@
 #! /usr/bin/env python
-from __future__ import absolute_import
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 '''Test bitcoin module data handling'''
 
 import jmbitcoin as btc
@@ -16,15 +18,6 @@ def test_bad_code_string():
         with pytest.raises(ValueError) as e_info:
             btc.get_code_string(i)
 
-@pytest.mark.parametrize(
-    "st, frm, to, minlen, res",
-    [
-        ("0101aa", 16, 16, 12, "0000000101aa"),
-    ])
-def test_changebase(st, frm, to, minlen, res):
-    assert btc.changebase(st, frm, to, minlen) == res
-
-
 #Tests of compactsize encoding, see:
 #https://bitcoin.org/en/developer-reference#compactsize-unsigned-integers
 #note that little endian is used.
diff --git a/jmbitcoin/test/test_ecc_signing.py b/jmbitcoin/test/test_ecc_signing.py
index b201dd1..fa489b3 100644
--- a/jmbitcoin/test/test_ecc_signing.py
+++ b/jmbitcoin/test/test_ecc_signing.py
@@ -1,5 +1,7 @@
 #! /usr/bin/env python
-from __future__ import absolute_import
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 '''Test ECDSA signing and other key operations, including legacy message
 signature conversion.'''
 
@@ -16,7 +18,7 @@ def test_valid_sigs(setup_ecc):
         msg = v['msg']
         sig = v['sig']
         priv = v['privkey']
-        assert sig == btc.ecdsa_raw_sign(msg, priv, True, rawmsg=True)+'01'
+        assert btc.from_string_to_bytes(sig) == btc.ecdsa_raw_sign(msg, priv, True, rawmsg=True)+b'01'
         #check that the signature verifies against the key(pair)
         pubkey = btc.privtopub(priv)
         assert btc.ecdsa_raw_verify(msg, pubkey, sig[:-2], True, rawmsg=True)
@@ -24,8 +26,8 @@ def test_valid_sigs(setup_ecc):
         for i in [0,1,2,4,7,25,55]:
             #corrupt one byte
             binsig = binascii.unhexlify(sig)
-            checksig = binascii.hexlify(binsig[:i] + chr(
-                (ord(binsig[i])+1) %256) + binsig[i+1:-1])
+            checksig = binascii.hexlify(binsig[:i] + btc.from_string_to_bytes(chr(
+                (ord(binsig[i:i+1])+1) %256)) + binsig[i+1:-1])
             
             #this kind of corruption will sometimes lead to an assert
             #failure (if the DER format is corrupted) and sometimes lead
@@ -36,6 +38,7 @@ def test_valid_sigs(setup_ecc):
                 continue
             assert res==False
 
+
 @pytest.fixture(scope='module')
 def setup_ecc():
     global vectors
diff --git a/jmbitcoin/test/test_keys.py b/jmbitcoin/test/test_keys.py
index f0f9c28..b1fdbc6 100644
--- a/jmbitcoin/test/test_keys.py
+++ b/jmbitcoin/test/test_keys.py
@@ -1,5 +1,7 @@
 #! /usr/bin/env python
-from __future__ import absolute_import
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 '''Public and private key validity and formatting tests.'''
 
 import jmbitcoin as btc
@@ -10,30 +12,30 @@ import os
 testdir = os.path.dirname(os.path.realpath(__file__))
 
 def test_read_raw_privkeys():
-    badkeys = ['', '\x07'*31,'\x07'*34, '\x07'*33]
+    badkeys = [b'', b'\x07'*31,b'\x07'*34, b'\x07'*33]
     for b in badkeys:
         with pytest.raises(Exception) as e_info:
             c, k = btc.read_privkey(b)
-    goodkeys = [('\x07'*32, False), ('\x07'*32 + '\x01', True)]
+    goodkeys = [(b'\x07'*32, False), (b'\x07'*32 + b'\x01', True)]
     for g in goodkeys:
         c, k = btc.read_privkey(g[0])
         assert c == g[1]
 
 def test_wif_privkeys_invalid():
     #first try to create wif privkey from key of wrong length
-    bad_privs = ['\x01\x02'*17] #some silly private key but > 33 bytes
+    bad_privs = [b'\x01\x02'*17] #some silly private key but > 33 bytes
 
     #next try to create wif with correct length but wrong compression byte
-    bad_privs.append('\x07'*32 + '\x02')
+    bad_privs.append(b'\x07'*32 + b'\x02')
     
     for priv in bad_privs:
         with pytest.raises(Exception) as e_info:
             fake_wif = btc.wif_compressed_privkey(binascii.hexlify(priv))
 
     #Create a wif with wrong length
-    bad_wif1 = btc.bin_to_b58check('\x01\x02'*34, 128)
+    bad_wif1 = btc.bin_to_b58check(b'\x01\x02'*34, b'\x80')
     #Create a wif with wrong compression byte
-    bad_wif2 = btc.bin_to_b58check('\x07'*33, 128)
+    bad_wif2 = btc.bin_to_b58check(b'\x07'*33, b'\x80')
     for bw in [bad_wif1, bad_wif2]:
         with pytest.raises(Exception) as e_info:
             fake_priv = btc.from_wif_privkey(bw)
@@ -47,7 +49,7 @@ def test_wif_privkeys_invalid():
         bad_key = k[0]
         for netval in ["mainnet", "testnet"]:
             #if using pytest -s ; sanity check to see what's actually being tested
-            print 'testing this key: ' + bad_key
+            print('testing this key: ' + bad_key)
             #should throw exception
             with pytest.raises(Exception) as e_info:
                 from_wif_key = btc.from_wif_privkey(bad_key,
@@ -55,7 +57,7 @@ def test_wif_privkeys_invalid():
                 #in case the b58 check encoding is valid, we should
                 #also check if the leading version byte is in the
                 #expected set, and throw an error if not.
-                if chr(btc.get_version_byte(bad_key)) not in '\x80\xef':
+                if chr(btc.get_version_byte(bad_key)) not in b'\x80\xef':
                     raise Exception("Invalid version byte")
 
 def test_wif_privkeys_valid():
@@ -66,14 +68,14 @@ def test_wif_privkeys_valid():
         key, hex_key, prop_dict = a
         if prop_dict["isPrivkey"]:
             netval = "testnet" if prop_dict["isTestnet"] else "mainnet"
-            print 'testing this key: ' + key
-            assert chr(btc.get_version_byte(
-                key)) in '\x80\xef', "not valid network byte"
+            print('testing this key: ' + key)
+            assert btc.get_version_byte(
+                key) in b'\x80\xef', "not valid network byte"
             comp = prop_dict["isCompressed"]
             from_wif_key = btc.from_wif_privkey(
                 key,
                 compressed=comp,
-                vbyte=btc.get_version_byte(key)-128)
+                vbyte=btc.from_int_to_byte(btc.from_byte_to_int(btc.get_version_byte(key))-128))
             expected_key = hex_key
             if comp: expected_key += '01'
             assert from_wif_key == expected_key, "Incorrect key decoding: " + \
diff --git a/jmbitcoin/test/test_main.py b/jmbitcoin/test/test_main.py
index 1532eed..2caf52f 100644
--- a/jmbitcoin/test/test_main.py
+++ b/jmbitcoin/test/test_main.py
@@ -1,5 +1,7 @@
 #! /usr/bin/env python
-from __future__ import absolute_import
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 '''Testing mostly exceptional cases in secp256k1_main.
    Some of these may represent code that should be removed, TODO.'''
 
@@ -22,7 +24,7 @@ def test_lpad():
     assert btc.lpad("aaaa", "b", 3) == "aaaa"
     
 def test_safe_from_hex():
-    assert btc.safe_from_hex('ff0100') == '\xff\x01\x00'
+    assert btc.safe_from_hex('ff0100') == b'\xff\x01\x00'
 
 def test_hash2int():
     assert btc.hash_to_int("aa"*32) == \
@@ -30,9 +32,9 @@ def test_hash2int():
 
 @btc.hexbin
 def dummyforwrap(a, b, c, d="foo", e="bar"):
-    newa = a+"\x01"
+    newa = a+b"\x01"
     x, y = b
-    newb = [x+"\x02", y+"\x03"]
+    newb = [x+b"\x02", y+b"\x03"]
     if d == "foo":
         return newb[1]
     else:
@@ -41,7 +43,7 @@ def dummyforwrap(a, b, c, d="foo", e="bar"):
 def test_hexbin():
     assert dummyforwrap("aa", ["bb", "cc"], True) == "cc03"
     assert dummyforwrap("aa", ["bb", "cc"], True, d="baz") == "bb02"
-    assert dummyforwrap("\xaa", ["\xbb", "\xcc"], False) == "\xcc\x03"
+    assert dummyforwrap(b"\xaa", [b"\xbb", b"\xcc"], False) == b"\xcc\x03"
 
 def test_add_privkeys():
     with pytest.raises(Exception) as e_info:
@@ -54,7 +56,7 @@ def test_ecdsa_raw_sign():
     assert e_info.match("Invalid hash input")
     #build non-raw priv object as input
     privraw = "aa"*32
-    msghash = "\xbb"*32
+    msghash = b"\xbb"*32
     sig = binascii.hexlify(btc.ecdsa_raw_sign(msghash, privraw, False, rawpriv=False, rawmsg=True))
     assert sig == "3045022100b81960b4969b423199dea555f562a66b7f49dea5836a0168361f1a5f8a3c8298022003eea7d7ee4462e3e9d6d59220f950564caeb77f7b1cdb42af3c83b013ff3b2f"
 
diff --git a/jmbitcoin/test/test_tx_serialize.py b/jmbitcoin/test/test_tx_serialize.py
index c538efb..e145a87 100644
--- a/jmbitcoin/test/test_tx_serialize.py
+++ b/jmbitcoin/test/test_tx_serialize.py
@@ -1,3 +1,6 @@
+from __future__ import (absolute_import, division,
+                        print_function, unicode_literals)
+from builtins import * # noqa: F401
 import jmbitcoin as btc
 import pytest
 import json
@@ -228,7 +231,7 @@ def test_serialization_roundtrip2():
         #ignore comment entries
         if len(j) < 2:
             continue
-        print j
+        print(j)
         deserialized = btc.deserialize(str(j[0]))
-        print deserialized
+        print(deserialized)
         assert j[0] == btc.serialize(deserialized)
diff --git a/jmclient/jmclient/btc.py b/jmclient/jmclient/btc.py
index 6ea8119..dac9d88 100644
--- a/jmclient/jmclient/btc.py
+++ b/jmclient/jmclient/btc.py
@@ -2,8 +2,8 @@
 different codebase than joinmarket's own.
 """
 #Protocol constants
-BTC_P2PK_VBYTE = {"mainnet": 0x00, "testnet": 0x6f}
-BTC_P2SH_VBYTE = {"mainnet": 0x05, "testnet": 0xc4}
+BTC_P2PK_VBYTE = {"mainnet": b'\x00', "testnet": b'\x6f'}
+BTC_P2SH_VBYTE = {"mainnet": b'\x05', "testnet": b'\xc4'}
 PODLE_COMMIT_FILE = None
 
 from jmbase.support import get_log
@@ -138,22 +138,11 @@ except ImportError:
     
     def b58check_to_bin(addr, version=False):
         """optionally include the version byte for get_version_byte.
-        Note that jmbitcoin does not need this flag, because it
-        uses the changebase() function, which here has been restricted.
         """
         if not version:
             return ebt.DecodeBase58Check(addr)[1:]
         else:
             return ebt.DecodeBase58Check(addr)
-    
-    def changebase(inp, frm=256, to=58):
-        """Implementation of base58 (*not* b58check) conversion
-        only. Used in message channel verifiable nick construction.
-        Explicitly disabling any other conversion for now.
-        """
-        if not (frm==256 and to==58):
-            raise NotImplementedError
-        return ebt.base_encode(inp, 58)
 
     def address_to_script(addr):
         return etr.Transaction.pay_script(ebt.TYPE_ADDRESS, addr)
diff --git a/jmclient/jmclient/client_protocol.py b/jmclient/jmclient/client_protocol.py
index 24e9fe3..1e4134d 100644
--- a/jmclient/jmclient/client_protocol.py
+++ b/jmclient/jmclient/client_protocol.py
@@ -62,7 +62,7 @@ class JMClientProtocol(amp.AMP):
         self.nick_pubkey = btc.privtopub(self.nick_priv)
         self.nick_pkh_raw = hashlib.sha256(self.nick_pubkey).digest()[
                     :self.nick_hashlen]
-        self.nick_pkh = btc.changebase(self.nick_pkh_raw, 256, 58)
+        self.nick_pkh = btc.b58encode(self.nick_pkh_raw)
         #right pad to maximum possible; b58 is not fixed length.
         #Use 'O' as one of the 4 not included chars in base58.
         self.nick_pkh += 'O' * (self.nick_maxencoded - len(self.nick_pkh))
@@ -111,9 +111,9 @@ class JMClientProtocol(amp.AMP):
         nick_stripped = nick[2:2 + max_encoded]
         #strip right padding
         nick_unpadded = ''.join([x for x in nick_stripped if x != 'O'])
-        if not nick_unpadded == btc.changebase(nick_pkh_raw, 256, 58):
+        if not nick_unpadded == btc.b58encode(nick_pkh_raw):
             jlog.debug("Nick hash check failed, expected: " + str(nick_unpadded)
-                       + ", got: " + str(btc.changebase(nick_pkh_raw, 256, 58)))
+                       + ", got: " + str(btc.b58encode(nick_pkh_raw)))
             verif_result = False
         d = self.callRemote(commands.JMMsgSignatureVerify,
                             verif_result=verif_result,
diff --git a/jmclient/jmclient/cryptoengine.py b/jmclient/jmclient/cryptoengine.py
index 693dd5f..62d1901 100644
--- a/jmclient/jmclient/cryptoengine.py
+++ b/jmclient/jmclient/cryptoengine.py
@@ -3,6 +3,7 @@ from __future__ import print_function, absolute_import, division, unicode_litera
 
 from binascii import hexlify, unhexlify
 from collections import OrderedDict
+import struct
 
 
 from . import btc
@@ -12,7 +13,7 @@ from .configure import get_network
 TYPE_P2PKH, TYPE_P2SH_P2WPKH, TYPE_P2WPKH = range(3)
 NET_MAINNET, NET_TESTNET = range(2)
 NET_MAP = {'mainnet': NET_MAINNET, 'testnet': NET_TESTNET}
-WIF_PREFIX_MAP = {'mainnet': 0x80, 'testnet': 0xef}
+WIF_PREFIX_MAP = {'mainnet': b'\x80', 'testnet': b'\xef'}
 BIP44_COIN_MAP = {'mainnet': 2**31, 'testnet': 2**31 + 1}
 
 
@@ -123,11 +124,11 @@ class BTCEngine(object):
     @classmethod
     def wif_to_privkey(cls, wif):
         raw = btc.b58check_to_bin(wif)
-        vbyte = btc.get_version_byte(wif)
+        vbyte = struct.unpack('B', btc.get_version_byte(wif))[0]
 
-        if (btc.BTC_P2PK_VBYTE[get_network()] + cls.WIF_PREFIX) & 0xff == vbyte:
+        if (struct.unpack('B', btc.BTC_P2PK_VBYTE[get_network()])[0] + struct.unpack('B', cls.WIF_PREFIX)[0]) & 0xff == vbyte:
             key_type = TYPE_P2PKH
-        elif (btc.BTC_P2SH_VBYTE[get_network()] + cls.WIF_PREFIX) & 0xff == vbyte:
+        elif (struct.unpack('B', btc.BTC_P2SH_VBYTE[get_network()])[0] + struct.unpack('B', cls.WIF_PREFIX)[0]) & 0xff == vbyte:
             key_type = TYPE_P2SH_P2WPKH
         else:
             key_type = None
diff --git a/jmclient/jmclient/maker.py b/jmclient/jmclient/maker.py
index 90c180b..bf1b858 100644
--- a/jmclient/jmclient/maker.py
+++ b/jmclient/jmclient/maker.py
@@ -7,6 +7,7 @@ import sys
 from binascii import unhexlify
 
 import btc
+from btc import SerializationError, SerializationTruncationError
 from jmclient.configure import jm_single
 from jmbase.support import get_log
 from jmclient.support import (calc_cj_fee)
@@ -110,7 +111,7 @@ class Maker(object):
         """
         try:
             tx = btc.deserialize(txhex)
-        except IndexError as e:
+        except (IndexError, SerializationError, SerializationTruncationError) as e:
             return (False, 'malformed txhex. ' + repr(e))
         jlog.info('obtained tx\n' + pprint.pformat(tx))
         goodtx, errmsg = self.verify_unsigned_tx(tx, offerinfo)
diff --git a/jmclient/test/commontest.py b/jmclient/test/commontest.py
index 9ce12c2..e5795e9 100644
--- a/jmclient/test/commontest.py
+++ b/jmclient/test/commontest.py
@@ -149,7 +149,6 @@ def make_sign_and_push(ins_full,
     binarize_tx(de_tx)
     de_tx = wallet.sign_tx(de_tx, scripts, hashcode=hashcode)
     #pushtx returns False on any error
-    print(de_tx)
     tx = binascii.hexlify(btc.serialize(de_tx))
     push_succeed = jm_single().bc_interface.pushtx(tx)
     if push_succeed:
diff --git a/jmdaemon/test/test_message_channel.py b/jmdaemon/test/test_message_channel.py
index 15f41b5..9f54beb 100644
--- a/jmdaemon/test/test_message_channel.py
+++ b/jmdaemon/test/test_message_channel.py
@@ -27,7 +27,7 @@ def make_valid_nick(i=0):
     nick_priv = hashlib.sha256(chr(i)*16).hexdigest() + '01'
     nick_pubkey = bitcoin.privtopub(nick_priv)
     nick_pkh_raw = hashlib.sha256(nick_pubkey).digest()[:NICK_HASH_LENGTH]
-    nick_pkh = bitcoin.changebase(nick_pkh_raw, 256, 58)
+    nick_pkh = bitcoin.b58encode(nick_pkh_raw)
     #right pad to maximum possible; b58 is not fixed length.
     #Use 'O' as one of the 4 not included chars in base58.
     nick_pkh += 'O' * (NICK_MAX_ENCODED - len(nick_pkh))
diff --git a/scripts/obwatch/ob-watcher.py b/scripts/obwatch/ob-watcher.py
index 8760f53..46ffef4 100644
--- a/scripts/obwatch/ob-watcher.py
+++ b/scripts/obwatch/ob-watcher.py
@@ -412,7 +412,7 @@ def get_dummy_nick():
     privacy, a conformant nick is created based on a random
     pseudo-pubkey."""
     nick_pkh_raw = hashlib.sha256(os.urandom(10)).digest()[:NICK_HASH_LENGTH]
-    nick_pkh = btc.changebase(nick_pkh_raw, 256, 58)
+    nick_pkh = btc.b58encode(nick_pkh_raw)
     #right pad to maximum possible; b58 is not fixed length.
     #Use 'O' as one of the 4 not included chars in base58.
     nick_pkh += 'O' * (NICK_MAX_ENCODED - len(nick_pkh))