Bitcoin Proof of Payment

Andy OfieshSenior Software EngineerArmory Technologies, Inc.

MIT Bitcoin Expo, March 7 & 8th, 2014

© Armory Technologies, Inc. 2014

Who am I?

Why am I here?

© Armory Technologies, Inc. 2014

What Does Armory Do?• First release in Dec 2011

• Open-source Bitcoin security wallet software

• Featured on Bitcoin.org for free

• Original innovator of cold-storage

• Current leading innovator of cold multi-sig storage

© Armory Technologies, Inc. 2014

• Lots of companies trying to bring Bitcoin to grandma

• Armory is bringing Bitcion to enterprises

• Armory free is for users protecting their own money

• Armory Quorum™ is for enterprises using employees to manage coins

– Distributed security

– Auditable, multi-user key management

– Full API for network/service integration (armoryd)

What is Proof of Payment?

Because Bitcoin converts money into public data, anyone can programmatically answer the question, “Did you pay for that?”

© Armory Technologies, Inc. 2014

By “anyone” I mean that any program can access the block chain to answer this question without using a trusted 3rd party.

How does it work?Proof of payment follows these steps:

1. Payer signs a message requesting something from payee

2. Payee receives the request, verifies the payer’s message was signed, and now has the payer’s bitcoin address.

3. Payee references the payer’s bitcoin address in the block chain to get the amounts paid and when.

4. Payee assesses payment and decides to either respond to the request or show a QR code to pay.

© Armory Technologies, Inc. 2014

Why should I care?

1. Everything that the payer and payee are doing can be done in a program.

2. Both can be anonymous.

3. Both can be program themselves

© Armory Technologies, Inc. 2014

Anonymity

Bitcoin allows anonymity, but it does guarantee it.

Things you can do to improve your anonymity

1. Single use addresses

2. Hold your own private keys

3. Coin Mixing

4. Cleaning Dust

5. Don’t use exchanges

6. Do/sell things for BTC

7. Write a piece of software using proof of payment.

© Armory Technologies, Inc. 2014

Tools

• BitcoinD

• ArmoryD

• Armory Python Scripting Tools– https://bitcoinarmory.com/using-armory-python

• Block Chain Info– https://blockchain.info

• BitcoinJ– http://bitcoinj.github.io

• Peter Todd’s – python-bitcoinlib– https://github.com/petertodd/python-bitcoinlib

© Armory Technologies, Inc. 2014

Lucy Van Pelt

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Five Cents Please

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Robot Lucy Van Pelt

© Armory Technologies, Inc. 2014

https://github.com/etotheipi/BitcoinArmory/tree/RobotLVP

Robot LVP Vulnerabilities

• A user could share their private key that paid for the service.

• A user could create a signer that does not reveal the private key to people sharing access.

• Software could be copied and the payment address changed.

© Armory Technologies, Inc. 2014

Robot LVP Contest Requirements

2 BTC will be paid to a program with these requirements

• Verify Payment on the Bitcoin Mainnet Blockchain

• Accept payment for 5 millibits

• Accept a request message if and only if it is signed by the private key that paid the fee

• Payment expires after 1 year

• If no valid payment is found, show the QR code to pay

• Verify that payment address has at least .1 millibits

• Submit your program to andy@bitcoinarmory.com by April 1st

© Armory Technologies, Inc. 2014