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Archive for January, 2015

Top secret free information

January 26th, 2015 No comments

I may or may not have been at a top secret hackathon at the weekend.

Secret hackathon wording

If you read the above text please leave your contact details in the comments so I can arrange to have somebody come round and shoot you.

In other news, I saw last week that the European Delegated Act requires that the European Space Agency to provide “Free and open access to Sentinel satellite data…” A requirement that is not incompatible with the wording above.

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Live coding, where should I send my invoice for performance royalties?

January 19th, 2015 4 comments

Live coding (i.e., performance art + coding) is the shiny new thing in trendy circles (which is why it was a while before I heard about it). I’m sure readers have had the experience of having to code around issues on customer sites while everyone looked on, this is certainly a performance and there is an art to making it look like minor issues, rather than major problems, are being sorted out.

Isn’t musical improvisation live coding? Something that people like J. S. Bach were doing hundreds of years ago.

I don’t think that the TOPLAP (Transdimensional Organisation for the Permanence of Live Algorithm Programming) website is aimed at people like me, but I did enjoy the absurdity of its manifesto.

Who originated the term live coding? Perhaps it was a salesman trying to turn the poor user interface on the product he was peddling into desirable feature, i.e., having to write code to get the instrument to play a tune is a benefit.

Live performers are always looking for a new angle to attract the public. Perhaps they have noticed the various efforts to get kids coding and have adapted the message to their own ends. No, that cannot be true, academics are making arduous journeys to German country houses to discuss this emerging new technology Don’t worry if you missed out, you can attend the First Live Coding International Conference in July!

I’m sure live coding will get a few students programming who would otherwise have gone off and done something else. But then so would a few rainy weekends.

I suspect that most developers would prefer to do fewer live coding sessions.

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My 2cents on the design of the contract language in Ethereum

January 12th, 2015 No comments

My previous post on Ethereum contracts got me thinking about how Ethereum should be going about creating a language and virtual machine for the contracts aspect of their cryptocurrency.

I would base the contract development gui on Scratch. Contract development will involve business people and having been extensively field tested on children Scratch stands some chance of being usable for business types.

For the language itself I would find a language already being used for contract related programming and simply adopt it.

At the moment the internal specification of contracts is visible for all to see. I expect a lot of people will be unwilling to share contract information with anybody outside of those they are dealing with. The Ethereum Virtual Machine needs to include opcodes that perform Homomorphic encryption, i.e., operations on encrypted values producing a result that is the encrypted version of the result from performing the same operation on the unencrypted values. Homomorphic encryption operations would allow writers of contracts that keep sensitive numeric values secret, they get to decide who gets a copy of thee dencryption keys needed to see the plain-text result.

The only way I see of overcoming the denial-of-service attack outlined in my previous post is to require that the miner who receives payment for executing a contract prove that they did the work of executing the contract by including program values existing at various randomly chosen points of contract execution.

Ethereum contracts, is the design viable?

January 11th, 2015 4 comments

I went to a workshop run by Ethereum today, to learn about cryptocurrency/virtual currency from a developer’s point of view. Ethereum can be thought of as Bitcoin+contracts; they are also doing various things to address some of the design problems experienced by Bitcoin. This article is about the contract component of Ethereum, which is being promoted as its unique selling point.

The Ethereum people talk so much about contacts that I thought once currency (known as ether, a finney is a thousandth of an ether, with other names going down to 10^{-18}) had been mined it was not considered legal tender until it was associated with the execution of a contract. In fact people will be free to mine as many ethers as they like without having any involvement with the contract side of things.

Ethereum expect the computational cost of mining to be significantly greater than the cost of executing contracts.

A contract is a self-contained piece of code created by a client and executed by a miner (the client pays the miner for this service). The result of executing the contract is added to the data associated with a block of mined currency (only one contract per block).

How confident can the client, and interested third parties, be that the miner paid to execute the contract is telling the truth and didn’t make up the data included in the mined currency block?

The solution adopted by Ethereum is to require all miners involved in the execution of contracts to execute all contracts that have been associated with mined currency, so that the result posted by the miner who got paid to execute each contract can be validated (51% agreement is required).

For this design to work, the cost of executing contracts to verify the data produced by other miners has to be small relative to paid income received from executing contracts.

If somebody is in the ether mining business, executing contracts has the potential to provide additional income for a small increase in effort, i.e., the currency has been mined why not get paid to execute contracts, adding the resulting data to blocks that have been mined?

Ethereum has specified the relative cost of operations executed by the Ethereum Virtual Machine. The Client specifies a value used to multiply these costs to produce an actual cost per operation that are willing to pay.

Requiring the community of contract executors to execute all contracts creates a possible vulnerability that can be exploited.

To profit from executing contracts the following condition must hold:

N_c A_o E_c < A_o P_o

where: N_c is the ratio of unpaid to paid contracts, A_o is the average number of operations performed per contract, E_c is the average execution cost per operation and P_o is the average amount clients pay per operation.

This simplifies to:

N_c {E_c/P_o} < 1

What would be a reasonable estimate for N_c, the ratio of unpaid to paid contracts? Would 1,000 miners offering contract execution services be a reasonable number? If we assume that contracts are evenly distributed among everybody involved in contract execution, then there are disincentives of scale; every new market entrant reduces income and increases costs for existing members.

What if businessman Bob wants to corner the contract market and decides to drive up the cost of executing contracts for all miners except himself? To do this he enlists the help of accomplice Alice as a client offering contracts at extremely poorly paid rates, which Bob is happy to accept and be paid for appearing to execute them (Alice has told him the result of executing the contracts); these contracts are expensive to execute, but Bob and Alice know number theory and don’t need a computer to figure out the results.

So Bob, Alice and all their university chums flood the Ethereum currency world with expensive to compute contracts. What conditions need to hold for them to continue profiting from executing contracts?

Lets assume that expensive contracts dominate, then the profitability condition becomes:

M_n N_c M_a A_o M_e E_c < A_o P_o

where: M_e is the increase in the number of contracts, M_a the increase in the average number of operations performed per contract and M_e the increase in average execution cost per operation.

This simplifies to:

M_n M_a M_e N_c {E_c/P_o} < 1

What values do we assign to the three multipliers: M_n M_a M_e? Lets say M_n=5,  M_a=10, M_e=3, which tells us that the price paid has to increase by a factor of 150 for those involved in the market to maintain the same profit level.

Given that Ethereum are making such a big fuss about contracts I had expected the language being used to express contracts to be tailored to that task. No such luck. Serpent is superficially Python-like, with the latest release moving in a Perl-ish direction, not in themselves a problem. The problem is that the languages is not business oriented, let alone contract oriented, and is really just a collection of features bolted together (the self absorbed use case for the new float type: “… elliptic curve signature pubkey recovery code…”, says it all). Another Ethereum language Mutan is claimed to be C-like; well, it does use curly brackets rather than indentation to denote scope.

If Ethereum does fly, then there is an opportunity for somebody to add-on a domain specific language for contracts, one that has the kind of built in checks that anybody involved with contracting will want to use t prevent expensive mistakes being made.

Users of Open source software are either the product or are irrelevant

January 9th, 2015 1 comment

Users of software often believe that the people who produced it are interested in the views and opinions of their users.

In a commercial environment there are producers who are interested in what users have to say, because of the financial incentive, and some Open source software exists within this framework, e.g., companies selling support services for the code they have Open sourced.

Without a commercial framework why would any producer of Open source be interested in the views and opinions of users? Answers include:

  • users are the product: I have met developers who are strongly motivated by the pleasure they get from being at the center of a community, i.e., the community of people using the software that they are actively involved in creating,
  • users are irrelevant: other developers are more strongly motivated by the pleasure of building things and in particular building using what are considered to be the right tools and techniques, i.e., the good-enough approach is not considered to be good-enough.

How do these Open source dynamics play out in the evolution of software systems?

It is the business types who are user oriented or rather source of money oriented. They are the people who stop developers from upsetting customers by introducing incompatibilities with previous releases, in fact a lot of the time its the business types pushing developers to concentrate on fixing problems and not wasting time doing more interesting stuff.

Keeping existing customers happy often means that products change slowly and gradually ossify (unless the company involved has a dominant market position that forces users to take what they are given).

A project primarily fueled its developers’ desire for pleasure cannot stand still, it has to change. Users who complain that change has an impact on their immediate need for compatibility get told that today’s pain is necessary for a brighter future tomorrow.

An example of users as the product is gcc. Companies pay people to work on gcc because they want access to the huge amount of software written by ‘the product’ using gcc.

As example of users as irrelevant is llvm. Apple is paying for llvm to happen and what does this have to do with anybody else using it?

The users of Angular.js now know what camp they are in.

As Bob Dylan pointed out: “Just because you like my stuff doesn’t mean I owe you anything.”