Matthew Roberts

I am a cryptobiologist specializing in the study of digital life forms like blockchains and certain kinds of unbounded smart contracts. “We must not let our politics harm these beautiful creatures.” – Myself.

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Atomic kidney-swap contracts to improve exchange liquidity across blockchains

Update 26 May 2017 - the 3 of 6 multi-sig scheme has an obvious race condition. This problem can be fixed by using a 4 of 7 scheme that looks like future, future, y1, xy, current, x1, and x2 public keys where xy becomes a special key with new consensus rules based on homomorphic secret sharing (will define this in more detail tomorrow.) 4 of 8 might also work where the keys would be future1, future2, y1, y2, current1, x1, x2, x3 but I’ll need to work out how to reduce the key no first.

Update 2: The existence of valid signatures that come from a secret and which utilise knowledge of future or current owner outside of the expected reveal periods imply that the exchange is attempting to attack the process. Fortunately, this can be added to the protocol too as ECDSA sigs can be directly validated from within Ethereum. Thus the entire scheme can so far be reduced to a 3 of 4 multi sig...

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What I think ShapeShift’s new Prism platform will be like

In about 12 days will announce details of their new system “built entirely on smart-contracts.” I don’t want to jump to conclusions here but if this is what I think it is – this could be the start of a very, very significant trend towards the big players in cryptocurrency exchange providing their customers with a much higher level of security.

For anyone who has been following these technologies you’ll notice that there hasn’t been any major companies trying to tackle “decentralized exchange.” I know of only a few companies who have tried to do this since 2013 and none of them managed to raise more than a few hundred K.

There are a few different reasons for this but what I think it comes down to is cost: it is far cheaper and easier to build a regular exchange and market it as a high security exchange then it is to do the opposite. So with ShapeShift’s Prism - I think it...

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Hundreds of lines of complex Bitcoin hacks reduced to a simple Solidity contract. Wow.

A couple of years back I was working on a smart contract in Bitcoin that implemented pay for private key contracts. The idea was that you can setup a contract to pay someone for releasing the details that allow a particular ECDSA Bitcoin private key to be extracted and payment is obviously conditional on the solution being correct.

In Bitcoin this is really damn complicated for a number of reasons. The first reason is that transaction IDs in Bitcoin can be randomly mutated so that chains of unconfirmed transactions can be invalided [0]. And the second reason is that all of the OP_CODES you need to create complex contracts in Bitcoin are either disabled or too limited to use.

That meant that the only way I could figure out how to get this contract to work on Bitcoin was to:

  1. Rely on a theoretical segwit existing (it’s not deployed yet) and
  2. Build a chain of transactions in such a way...

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A coin for security

Here’s another idea for a cryptocurrency - a coin that rewards people for the practices they use to secure their cryptocurrencies on other blockchains.

This can all be done without trust because many aspects of cryptocurrency security already depend on cryptographic proof. A brief list of things that a cryptocurrency like this might check for includes:

  • N factor auth and hardware devices used for multi-sig signing.
  • Fail-safe theft recovery procedures
  • Password complexity and rotation checks (like revealing hash-locked inputs.)
  • Cryptographically provable wallet backups.
  • Use of privacy enhancing protocols.
  • Use of secure exchanges to purchase coins.
  • Other, e.g. provably secure constructs, possibly with trusted computing.

There are so many different ways to protect crypto-assets and I’ve put a lot of thought into working them all out over the years. But in spite of this the biggest...

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Events are arbitrary

When I first got into Bitcoin my main area of interest was in smart contracts. I used to marvel at how the blockchain could be used to eliminate trust between people and I’d despair whenever an OP_CODE was removed (making the former harder to do.) But that’s only because I didn’t understand one subtle quality of how a blockchain works: events are arbitrary.


The blockchain really only has two qualities worth mentioning:

  1. It can securely order events on a network of untrusted computers.
  2. It defines an event called a transaction.

The second quality is optional [0]. It just so happens that in the case of Bitcoin enough information is already included with the software to describe what a “transaction” means so that now its become impossible to separate the network definition of “the blockchain” from “a transaction” [1].

But if you understand why this is then you understand that the...

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Update: 19/02/2017 - added discussion on hacker news.
I also added an example.
Update: 21/02/2017 - added discussion of obfuscated exploits, early disclosure penalties, incentives, and scalability

Bug bounties suck. Researchers routinely don’t get paid for their work and vendors continue to get away with the same shitty behavior. It’s a system that lacks any kind of accountability and only benefits the company.

Solution: Do it as a smart contract on a blockchain.

An example

  1. A smart contract to audit a C-based program is written. It includes a test case to see if a file with a specific name has been created under the process’ permissions. It also includes information about the program.
  2. A researcher finds a bug and uses it to write a buffer overflow exploit. The exploit is designed to pass the test case and is written using a special domain specific language for exploitable code for...

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Some simple smart contracts to dispel the hype

In the past I’ve said that “smart contracts” are protocols for exchanging crypto-payment for some kind of specialized product or service without the need for trust. But within the Bitcoin-space I still see many examples of things that shouldn’t really be called a smart contract at all.

So here are some examples of some smart contracts that clearly show how payment can be given for some kind of service that has then been intertwined with payments so closely that trust is removed.

I’ll start with the simplest contract I know of and move on to some new contracts that help demonstrate the idea behind universal verifiability in trustless trade protocols. Here is the first contract.

Example 1: Paying for a hash collision

value1 = get_input()
value2 = get_input()
btc_address = get_input()

 Values need to be different to prove a collision.
if value1 == value2:

if sha256(value1)

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What if smart contracts were a new web standard = new achievement unlocked?

Edit: thought of a catchy name for this – Smart REST.

Smart contracts are all about formalizing trust relationships in an effort to try reduce critical points of failure within an agreement. The idea is that instead of trusting that a person will carry out a given function - we clearly segregate and define those responsibilities which can then be tied to the conditional release of collateral, the change of reputation, the conclusion of a legal contract, and even actions taking place within the real world.

To do this we use cryptographic ledgers which offer us a way to securely and publicly record relationships between individuals. In the case of financial relationships – some of these relationships can be made 100% trustless by using cryptography (a godsend to finance) - and in other cases its usually possible to reduce the amount of trust involved by using things like distributed...

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How a super computer could prevent future exchange hacks

Emin Gün Sirer published a paper this year [0] that described “Bitcoin vaults” [1] - a new mechanism for forcing coins to be locking up for a certain amount of time before they can be spent. The idea is for the owner to be able to recover coins during a designated clearing phase whose progress is made publicly visible on the blockchain. The owner could then recover coins from transactions [2] that he or she didn’t authorize even if their private keys were compromised. This idea is genuinely revolutionary [10] as currently owners have no way to reverse payments if they get hacked.


If something like this had of existed before the recent Bitfinex hack we might have had a chance to prevent it. Unfortunately, schemes like this rely on having to change Bitcoin’s consensus rules which is a task that’s notoriously difficult to do. Only certain changes to the code can be safely made and it...

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Datachains: an AI driven DAS for incentivizing taste-based content delivery

Future decentralized autonomous systems (DAS) will likely be focused on distributing specialized AI agents for finding patterns in bulk data sets. These DAS will be funded with a pre-existing cryptocurrency like Bitcoin and then pegged to the entity in such a way that the assets can be given out as rewards for correct solutions without human intervention. The resulting system forms a decentralized, autonomous, peer-to-peer, client-to-client, datachain that rewards assets for finding data that the AI likes.

The use-cases for such a system would be in big data processing, web scraping, and data mining where remote files are scattered all over the Internet and are too resource intensive for any one organization to search for specific patterns. Such a system may help us to find new meaning in the vast stores of content already accessible via the Internet and what better example to start...

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