simple bitoin-like program

bitzap.py

#==========Bitzap: a tiny bitcoin-like program.==========#
# The goal is secure published transactions. Not yet completed.
# Install Notes:
#  Uses dbdict, a recipe from: http://code.activestate.com/recipes/576642-persistent-dict-with-multiple-standard-file-format/
#  On Ubuntu the Crypto library can be installed with "sudo apt-get install python-crypto"
# Details:
#  Addresses are first 32 chars of a hash of the public key.
#  Transaction IDs are first 32 chars of the buyer's signature.
#  Receipts are lists of debits and credits that have been applied to each address.
#  Buyer is sender, seller is receiver.
#===============================#
from Crypto.Hash import SHA256
from Crypto.PublicKey import RSA
from Crypto import Random
import time
#from dbdict import PersistentDict
from pprint import pprint
#===============================#
#d = PersistentDict('bitzap.json',flag='c',format='json')
def r(): return Random.new().read
def k(): return RSA.generate(1024,r())
def newitem():
    key=k(); pkey=key.publickey()
    text=pkey.exportKey()
    return SHA256.new(text).hexdigest()[:32], key, pkey
def privateaddress(address, key, pkey):
    return {address:key.exportKey()}
def publicaddress(address, key, pkey):
    return {address:pkey.exportKey()}
def newaddress(d,item):
    d['private'].update(privateaddress(*item))
    d['public'].update(publicaddress(*item))
    d['receipt']['debit'].update({item[0]:[]})
    d['receipt']['credit'].update({item[0]:[]})
def newreciept(transid):
    buyer,seller,amount=transinfo(transid)[:3]
    d['receipt']['credit'][seller].append(transid)
    d['receipt']['debit'][buyer].append(transid)
#---lookup functions---#
def getpkey(address):
    text=d['public'][address]
    return RSA.importKey(text)
def getkey(address):
    text=d['private'][address]
    return RSA.importKey(text)
def transinfo(transid):
    return d['transaction'][transid][1]
def transbuyer(transid):
    return transinfo(transid)[0]
def transseller(transid):
    return transinfo(transid)[1]
def transamount(transid):
    return transinfo(transid)[2]
#---transaction functions---#
def createtransaction(buyer,seller,amount):
    key=getkey(buyer)
    transinfo=[buyer,seller,amount,time.ctime()]
    transtext=str(transinfo)
    transsig=key.sign(transtext,'')
    transid=str(transsig[0])[:32]
    return {transid:[transsig,transinfo]}
def addtransaction(buyer,seller,amount):
    trans=createtransaction(buyer,seller,amount)
    d['transaction'].update(trans)
    transid=trans.keys()[0]
    newreciept(transid)
    return transid
def verifytranssig(transid):
    trans=d['transaction'][transid]
    transsig=trans[0]
    transinfo=trans[1]
    pkey=getpkey(transinfo[0])
    return pkey.verify(str(transinfo),transsig)
def getamounts(address,transtype):
    translist=d['receipt'][transtype][address]
    total=[]
    for transid in translist:
        total.append(transamount(transid))
    return sum(total)
def verifytransamount(transid):
    available=getamounts(transbuyer(transid),'credit')-getamounts(transbuyer(transid),'debit')
    return available >= transamount(transid)
def verifytransaction(transid):
    return verifytranssig(transid) & verifytransamount(transid)
#---test---#
def init():
    d={}; d['private'],d['public'],d['transaction'],d['receipt']={},{},{},{'credit':{},'debit':{}}
    return d
d=init()
item=newitem()
newaddress(d,item)
buyer=item[0]
item=newitem()
newaddress(d,item)
seller=item[0]
amount=100
trans=addtransaction(buyer, seller, amount)
def p(text): pprint(d[text])
p('receipt')
print verifytransamount(trans)
def publishtrans(transid):
    transinfo=transinfo(transid)
    if verifytransaction(transid):
        sendtrans(transid)
    else:
        deletetrans(transid)
def deletetrans(transid):
    trans=d['transaction'].pop(transid)
    buyer,seller=trans[1][:2]
    d['receipt']['debit'].pop(buyer)
    d['receipt']['credit'].pop(seller)