Transaction Scripting

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Transcript Transaction Scripting

Bitcoin Transaction Scripting

MIT Bitcoin Expo, May 3rd, 2014

Andy Ofiesh

Senior Software Engineer Armory Technologies, Inc.

Who am I?

What have I done?

What am I doing?

What is a Transaction?

• • • • The Block chain has a list of Blocks A Block has a list Transactions (Tx) A Transaction has a list of Transaction Inputs (TxIn) and TransactionOutputs (TxOut) Each TxIn has a corresponding TxOut that it Spends. Some TxOuts are Unspent © Armory Technologies, Inc. 2014

What is a Transaction Script?

• • • • Transaction Scripts come in two parts.

A TxOut Script gives the puzzle that must be solved in order to spend a TxOut.

A TxIn Script (SigScript) gives the solution to a TxOut Script’s puzzle.

The two parts of the transaction script are executed when you try to spend a TxOut. 1 st execute your spending TxIn’s SigScript, then the spent TxOut’s Script. If there is no failure and the top of the stack is non-zero, then spending the TxOut is allowed.

Transaction Scripting Language

• • • • • Bitcoin is not just a value transfer system. It is a programmable money system.

Many types of contracts and escrow are possible.

https://en.bitcoin.it/wiki/Contracts Stack-Based (Forth-like) Not Turing-Complete (No loops) Language reference: https://en.bitcoin.it/wiki/Script © Armory Technologies, Inc. 2014

Standard Transaction Scripts

• – – – There 4 different Standard Transaction Types – Pay to Public Key (P2PK, generally used for mined Bitcoins) Pay to Public Key Hash (P2PKH) Multi-Signature M-of-N (MultiSig) Pay to Script Hash (P2SH) © Armory Technologies, Inc. 2014

Non-Standard Transaction Scripts

• • • • • There are many valid scripts that are not standard.

Most miners only mine standard scripts, but a few will mine non-standard scripts by request.

Most Bitcoin nodes won’t even forward non-standard transactions to peers.

Putting a non-standard transaction into a P2SH TxOut script makes the TxOut standard – Spending this TxOut is still non standard, but that’s the receiver’s problem Testnet considers all scripts standard.

Tools

• • • • • • Block Chain Info Bitcoin Armory Application Armory Python Scripting Tools – https://bitcoinarmory.com/developers/python-scripting/ BitcoinD Command Line BitcoinJ – https://code.google.com/p/bitcoinj/ Jeff Garzik’s – python-bitcoinlib – https://bitcointalk.org/index.php?topic=150436.0

Pay to Public Key Hash Example

TxOut Script 76 a9 14 9fde...4abe 88 ac TxIn Script OP_DUP OP_HASH160 Push 20 Public Key Hash OP_EQUALVERIFY OP_CHECKSIG 49 3046...b101 41 04c8...eb79

Push 65 (or 33) bytes – Public Key Push ~73 bytes – DER Encoded Signature Signature Public Key Signature Public Key Public Key Signature Pub Key Hash Public Key Signature Pub Key Hash Pub Key Hash Public Key Signature Public Key Signature OP_TRUE © Armory Technologies, Inc. 2014

Multi Signature

TxOut Script 52 41 041...6c84 41 04db...8751 41 043b...d649

53 ae OP_2 Push 65 (or 33) bytes – Public Key (times 3) OP_3 TxIn Script 00 48 3045...9c01 49 3046...e601 OP_CHECKMULTISIG OP_FALSE OP_FALSE Push ~73 bytes – DER Encoded Signature (times 2) Signature Signature OP_FALSE OP_2 Signature Signature OP_FALSE Pub Key Hash Pub Key Hash Pub Key Hash OP_2 Signature Signature OP_FALSE OP_3 Pub Key Hash Pub Key Hash Pub Key Hash OP_2 Signature Signature OP_FALSE OP_TRUE © Armory Technologies, Inc. 2014

Pay to Script Hash Example

TxOut Script a9 14 1451...dbc0 87 TxIn Script OP_HASH160 Push 20 Public Key Hash OP_EQUAL 48 3045...9c01 49 3046...e601 4c c9 5241...53ae Push ~73 bytes – DER Encoded Signature (times 2) Signature Signature Push 201 bytes - Serialized Script Serialized Script Signature Signature Script Hash Serialized Script Signature Signature Script Hash Script Hash Serialized Script Signature Signature OP_TRUE Serialized Script Signature Signature © Armory Technologies, Inc. 2014

MIT Expo Bitcoin Puzzles by Armory

• • • • 1 Bitcoin Treasure Hunt – Get Handout – https://blockchain.info/tx/6804a732fe2ca7a653b2a30580d2f035750114e02d5e1841512274b1eb45008a Total of 1 Bitcoin can be collected by solving all of these on Testnet: – – – – – http://blockexplorer.com/testnet/tx/4ad79d6373431defd0de6459368f7e295d674aa316293fc4a0b249567fb0f889 http://blockexplorer.com/testnet/tx/c5c6b5582ff9d572296e7af3d6821f103f88386ee9f77ffae78c2db45816b80e http://blockexplorer.com/testnet/tx/fb6839158e862a660d7d37cc1437805bbd4ad81d00fae28b9f58c72393c8a166 http://blockexplorer.com/testnet/tx/e83e207c0400df52785c2999785b25ea65f5e6ca5643caa6347f62d715b85777 http://blockexplorer.com/testnet/tx/2d931ffc545e9e42612d38cd6a8aa013256c9dedad3bc069336f9f6347abbd80 For helpful links and other resources visit: https://bitcoinarmory.com/developers/mit-expo/ For questions and to submit Testnet solutions send email to [email protected]