# Gavin Andresen
# 2010-09-13 12:38:24
# https://bitcointalk.org/index.php?topic=1026.msg12557#msg12557

This bitcoind address validator is a subclass of the Django forms.CharField class, but could easily be adapted to other frameworks or to be standalone code. @p{par}

It does a "deep" validation, checking that the checksum built into every bitcoin address matches the address. It needs the PyCrypto library for the SHA256 function. @p{par}

I hereby release this code into the public domain, do with it what you will.  And please let me know if you find any bugs in it. @p{par}

BCAddressField.py:
Code:
# @p{brk}
# DJango field type for a Bitcoin Address @p{brk}
# @p{brk}
import re @p{brk}
from django import forms @p{brk}
from django.forms.util import ValidationError @p{brk}
from Crypto.Hash import SHA256 @p{par}

class BCAddressField(forms.CharField): @p{brk}
  default_error_messages = { @p{brk}
    'invalid': 'Invalid Bitcoin address.', @p{brk}
    } @p{par}

  def __init__(self, *args, **kwargs): @p{brk}
    super(BCAddressField, self).__init__(*args, **kwargs) @p{par}

  def clean(self, value): @p{brk}
    value = value.strip() @p{brk}
    if re.match(r"[a-zA-Z1-9]{27,35}$", value) is None: @p{brk}
      raise ValidationError(self.error_messages['invalid']) @p{brk}
    version = get_bcaddress_version(value) @p{brk}
    if version is None: @p{brk}
      raise ValidationError(self.error_messages['invalid']) @p{brk}
    return value @p{par}

import math @p{par}

__b58chars = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz' @p{brk}
__b58base = len(__b58chars) @p{par}

def b58encode(v): @p{brk}
  """ encode v, which is a string of bytes, to base58.                                                                                                                @p{brk}
  """ @p{par}

  long_value = 0L @p{brk}
  for (i, c) in enumerate(v[::-1]): @p{brk}
    long_value += (256**i) * ord(c) @p{par}

  result = '' @p{brk}
  while long_value @s{gt}= __b58base: @p{brk}
    div, mod = divmod(long_value, __b58base) @p{brk}
    result = __b58chars[mod] + result @p{brk}
    long_value = div @p{brk}
  result = __b58chars[long_value] + result @p{par}

  # Bitcoin does a little leading-zero-compression:                                                                                                                   @p{brk}
  # leading 0-bytes in the input become leading-1s                                                                                                                    @p{brk}
  nPad = 0 @p{brk}
  for c in v: @p{brk}
    if c == '\0': nPad += 1 @p{brk}
    else: break @p{par}

  return (__b58chars[0]*nPad) + result @p{par}

def b58decode(v, length): @p{brk}
  """ decode v into a string of len bytes                                                                                                                             @p{brk}
  """ @p{brk}
  long_value = 0L @p{brk}
  for (i, c) in enumerate(v[::-1]): @p{brk}
    long_value += __b58chars.find(c) * (__b58base**i) @p{par}

  result = '' @p{brk}
  while long_value @s{gt}= 256: @p{brk}
    div, mod = divmod(long_value, 256) @p{brk}
    result = chr(mod) + result @p{brk}
    long_value = div @p{brk}
  result = chr(long_value) + result @p{par}

  nPad = 0 @p{brk}
  for c in v: @p{brk}
    if c == __b58chars[0]: nPad += 1 @p{brk}
    else: break @p{par}

  result = chr(0)*nPad + result @p{brk}
  if length is not None and len(result) != length: @p{brk}
    return None @p{par}

  return result @p{par}

def get_bcaddress_version(strAddress): @p{brk}
  """ Returns None if strAddress is invalid.  Otherwise returns integer version of address. """ @p{brk}
  addr = b58decode(strAddress,25) @p{brk}
  if addr is None: return None @p{brk}
  version = addr[0] @p{brk}
  checksum = addr[-4:] @p{brk}
  vh160 = addr[:-4] # Version plus hash160 is what is checksummed                                                                                                     @p{brk}
  h3=SHA256.new(SHA256.new(vh160).digest()).digest() @p{brk}
  if h3[0:4] == checksum: @p{brk}
    return ord(version) @p{brk}
  return None @p{brk}

@p{(bf}October 20:@p{bf)} Fixed bug with bitcoin addresses with leading-1's.