Bitrans

A bitcoin transaction script language / vm implementation in python. Built based on info from the bitcoin wiki.

Getting it running

• Install bitcoind
  • Guide for installing using Macports on Maverick guide
• Enable the bitcoin rpc server and historical transaction indexing in ~/bitcoin.conf by adding/uncommenting the following lines and replacing bracketed things:
  • txindex=1
  • server=1
  • rpcuser=[yourUser]
  • rpcpassword=[yourPass]
  • rpcport=8332
  • rpcconnect=127.0.0.1
• Spin up a bitcoind daemon, rebuilding the historical index. This will take some time to complete; about a day for all transactions. You will be able to work with the current state of the index, though, so transactions from early blocks should work pretty quickly.

bitcoind -conf=/path/to/your/bitcoin.conf -daemon -reindex

• Get bitrans:

git clone https://github.com/hackscience/bitrans.git
cd bitrans

• Install the python ecdsa lib.
• Fire up python:

python

• Establish a connection to the bitcoind daemon

>>> import rpc
>>> s = rpc.jsonrpc("yourUser","yourPass")

• Grab a transaction
  • the transaction id could be found in https://blockchain.info/
  • for testing, we use txid = ‘fff2525b8931402dd09222c50775608f75787bd2b87e56995a7bdd30f79702c4’.
  • Note that if your bitcoind hasn’t finished reindex, the current rpcserver will just return NoneType Error.Just grab a different txid or wait until reindex finishes.

>>> import transaction
>>> t = transaction.transaction('fff2525b8931402dd09222c50775608f75787bd2b87e56995a7bdd30f79702c4',s)

• Verify the transaction:

t.verify()

Description

this is outdated Here’s how it works:

There are three primary abstractions: opcodes, bytestreams, and machines. A stream is a sequence of bytes; it is implemented as a wrapper around python strings of human readable hex (like ‘AFAF’). A machine consists of two stacks (a primary and alternative stack). An opcode takes a stream and a machine as input and does stuff (maybe mutates) one, both, or neither.

Byte streams will be a mixture of opcodes and ‘raw’ data. The elements of the stacks are themselves bytestreams. Raw data is interpreted as variable-length little-endian signed integers. Opcodes are one-byte unsigned little-endian big-endian ints.

There doesn’t seem to be any reason to compile anything. A script is interpreted by continually reading an opcode from a stream representing the script and applying the opcode to the stream and a machine. I think scripts have headers but I haven’t quite figured it out yet. (Multiple) scripts are embedded in transactions which provide some metadata. A transaction is valid if all scripts do not fail during interpretation and the top stack item after interpretation is true.

Structure

• ops.py: Opcode implementations.
• opfns.py: Implementations of the functions that opcodes are built from.
• machine.py: Stack machine implementation.
• bytestream.py: Bytestream implementation.
• script.py: Implements a script.
• transaction.py: Parses and represents entire transactions.

Immediate todo

• Implement remaining opfns and ops

Fun todo

• Write a higher-level representation which compiles to bytestreams.
• Animate the process of interpreting a script.
• Throw a whole bunch of garbage at the vm and see if anything causes it to lock up or overflow or something.

Running tests

Install and run nose:

pip install nose
nosetests