Mike Hearn talks Hourglass Project and Avoiding Miner Fees

Hourglass is yet another promising project by BitcoinJ developer and former Google engineer Mike Hearn, which has already surpassed the crowdfunding goal for its initial design.

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Mike Hearn talks Hourglass Project and Avoiding Miner Fees

Hourglass is yet another promising project by BitcoinJ developer and former Google engineer Mike Hearn, which has already surpassed the crowdfunding goal for its initial design. Once the initial design is done, Hearn is planning to move forward to implement a real prototype of the service. CoinTelegraph reached out to Hearn to get some more insights about this project and what we can expect.


Hourglass is a specialized BTC wallet using bitcoin micropayment channels that allows users to pay per second. It can be used to pay for things like online lessons via Skype, consulting, internet radio and so on. Therefore, a person can get paid instantly for the amount of time they are spending.

According to the official design description, Hourglass would be built in the same style as Lighthouse and thus have the following features:

  • HD wallet that supports password protection and backup by writing down your 12 wallet words.
  • Simple but controllable threshold-signed online updates
  • Runs on Windows, Mac and Linux with potential for mobile versions in future.
  • Modern UI specifically tailored for the pay-per-second use case.

In contrast, the current financial architecture was never designed to handle micro transactions due to the limitations and friction of the credit card payment system, which was developed in the 1940’s and 50’s with other goals in mind.

However, bitcoin opened up a slew of new possibilities with its lower transaction fees enabling micro transactions whose processing costs previously rendered them unfeasible. Indeed, the biggest concern about any micro transaction services in any payment system is the transaction processing fees. But despite Bitcoin’s transactions having a fairly low fee (mining fee), the amount is nevertheless not negligible when we are talking about rolling, per second basis transactions.

Additionally, micropayment channels as shown in this video became possible by using the nLockTime feature in BTC transactions. Soon after that, many people went further and came up with numerous interesting ideas. But unfortunately, there has been a known issue with this method from the beginning, which in Bitcoin is called transaction malleability. Transaction malleability causes the ID of the transaction (hash of the whole transaction) to change, and as Hearn himself already mentioned, the whole micropayment channel is vulnerable to these attacks.

CoinTelegraph spoke to Hearn about the issue of mining fees, transaction malleability and other aspects with relation to the Hourglass project.

Mike Hearn

CoinTelegraph: How are you planning to deal with the mining fee in Hourglass?

Mike Hearn: The payment channels protocol allows for the avoidance of most miner fees by only placing two transactions onto the block chain rather than every single micropayment.

CT: Micropayment channels are all subject to transaction malleability. How do you deal with the malleability in Hourglass?

MH: Transaction malleability can be exploited to break the protocol and attempt to engage in a sort of ransom attempt, assuming the receiving party can communicate freely and anonymously with the sending party and assuming they win a network race. It's not very likely to be a problem in practice, but there is work being done (BIP 62) to fix malleability properly.

CT: Does Hourglass only work on desktop applications? Why don’t you consider web applications? Aren't they simpler to use for users?

MH: Good question - I will probably write an article on this at some point. Briefly, the web is a poor platform for app development in general but is extremely poor at making Bitcoin wallets for a host of technical reasons.

I don't agree that the web is simpler. It can be faster to get going if you're just experimenting with something, and assuming there's no registration requirement. But hundreds of millions of people have downloaded Skype, Spotify, iTunes, Google Earth, etc. On mobile, downloadable apps dominate. It's obviously not that complicated. On a good modern internet connection you can download Lighthouse in 30 seconds or so, without providing even your email address. Not a big deal.

CT: Hourglass seems to be a really interesting project that can be integrated with other services. Do you plan on integrating this service with other apps and services?

MH: It might be a feature of Lighthouse rather than a standalone app. I'm still thinking about it. It might also be worth integrating it with some kind of video streaming service as well.

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