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What’s Worrying/Exciting about Bitcoin in 2017



Looking forward into the next year and more of bitcoin, I see three main areas of concern, each related to the other. Let’s look at the problems, and the work going on to solve them.

  • Fungibility
  • Centralization
  • Scalability

Fungibility: Protecting Your Privacy

Fungibility technically means all coins are substitutable, but in practice it means that you can spend your bitcoins how you want. That means that nobody has the power to stop your transaction (see: Centralization), and nobody has reason not to accept your coins.

The state of fungibility in bitcoin today is poor. Services exist which aim to trace where bitcoins came from and whose they are. The fact that coins can be traced means some services are obliged to do so, and they refuse to interact with coins they see as “tainted”.

The simplest weakness of fungibility is the public ledger: everyone can try to analyze payments to see where they went. Consider transaction 3d96bcd… from April 8th 2016; one output is 3.10510875 BTC, the other is 0.05934611 BTC. If we convert them using the USD closing rate from April 7th, that’s $1307.8842 and $24.9968. It’s fair to guess that the second output is a $25 payment, and the first output is back to the payer. I’d also guess the payer is in the United States.

Addresses naturally cluster when a wallet has to use more than one input to create a transaction; when public addresses are revealed (particularly with address reuse!), analysis becomes easier. I asked someone to look at my bitcoin address, and he immediately linked me to using such techniques.

Different software creates slightly different transactions, which can also be used to link transactions and thus addresses. Differences in fee estimation is another method. And every transaction you know makes it easier to guess the remaining transactions, like solving a crossword puzzle. Fungibility is a network property: other people having it helps you have it, too.

There are also active probes going on; fake bitcoin nodes which connect to as many other nodes as they can, presumably to try to nail down the original source of transactions.

What’s Being Done For Fungiblity

Software is slowly improving: every bitcoin core release changelog seems to include tweaks to make active snooping more difficult.

We may see more uniformity in wallet implementations, too, though in the short term things like replace-by-fee will probably make wallets more different, not less.

The most promising development here is TumbleBit: it’s a tumbler which you don’t need to trust with your coins or your privacy. A normal tumbler is where I take everyone’s coins, and then return them randomly. Of course, I might decide to not return them, or keep records so I can trace whose coins went where. TumbleBit is more complicated, but doesn’t have either of these problems. It’s in early development, but once it’s complete I look forward to quite a few TumbleBit servers mudding the waters.

Centralization: Control of The Network

If the miners refuse to mine your transactions, your bitcoins aren’t worth anything. With better fungibility that becomes unlikely, but still possible (miners could insist on ID for every transaction, for example).

In most systems, there are economies of scale which drive centralization, and bitcoin mining is no exception. The invention of mining pools dramatically increased centralization, as small miners delegated their transaction selection to a handful of pools (this smooths out a miners income, by profit sharing). As block sizes increased, the situation became worse: if your block is slow to get out to the other miners, it’s likely to lose a race, and if you’re slow to get blocks from other miners, you’re more likely to produce obsolete blocks. Blocks which lose out like this are called “orphan blocks”, and how often you produce them is your “orphan rate”. More than 1% and your profitability is probably shot.

You can drop your orphan rate by being the biggest miner (or, part of the biggest pool). If a single miner or pool gets more than 50% (which has happened), they can reliably censor the network (which hasn’t). With even less they can still profitably exploit vendors who accept unconfirmed transactions (which has happened). And it turns out that larger miners can drive up orphan rates of other miners (so-called selfish mining) and magnify their advantage.

It should be no surprise then that mining is fairly centralized: four groups control more than half the mining power. Fortunately, there doesn’t seem to be deliberate orphaning attacks happening.

The other issue is that fear of orphaning leads to miners mining empty blocks (aka SPV mining). They do this because they watch other mining pools, and as soon as they see a block header which refers a new previous block, they start mining an empty block themselves. They have to mine an empty block, because they don’t know what transactions were in the previous block. That doesn’t help the network throughput at all, and because they are not validating the previous block, it greatly weakens the security of lightweight nodes which assume miners are actually checking blocks. It turns out over 50% of mining power was doing this in 2015, and many still are.

What’s Being Done For Centralization

Fast block propagation was a big area of work last year, with Bitcoin Unlimited’s XTHIN and Bitcoin Core’s Compact Block work. Both send short summaries of the block contents which often allow a node (which usually knows all the transactions already, just not which ones are in this block) to reconstruct it.

Matt Corallo previously ran the Bitcoin Relay Network to try to increase propagation and reduce incentive to SPV mine; the latest version is based on compact blocks and is even more efficient, called Bitcoin Fibre. You’re welcome to run your own Fibre network, too (I run a test one on Digital Ocean, for example). It uses UDP and error correction so you can get blocks from multiple sources at once, and handle packet loss. Matt claims that there’s no point in SPV mining any more; Fibre gets you the blocks just as fast.

There’s ongoing work on speeding up new block creation further: I’m told Bitcoin Unlimited removed the validity double-check on newly created blocks (it’s caught issues in the past, but maybe it’s time) and Bitcoin Core has worked on speeding it up so it’s no longer measurable. Combined with more significant fee income (which is lost when SPV mining), we may see SPV mining eliminated this year.

None of these addresses the core problem of centralization; this is the issue we have fewest technical fixes for and thus is likely to be least amenable to technical efforts.

Nontheless, Roger Ver’s mining pool gives me hope that we’ll see some diversity in motivations for miners. Making life easier and more convenient for small miners (especially solo mining) should be a priority for those who care about centralization. In the long term, as more businesses become dependent on bitcoin, I’d like them to start investing in mining capacity as a kind of distributed insurance policy.

Scalability: More Transactions

In the early days, bitcoin software had a 100k block limit and no transaction fees were required. Nobody cared, and blocks were never full.

When blocks passed 700k, bitcoin saw its first centralization crisis as orphan rates spiked and one pool ( got over 50% of the hash power. Since then developers have scrambled over the issue of block propagation; in theory, it could be independent of block size, but in practice it’s not. Centralization has remained a core source of tension with hopes for enlarging blocksize. Blocks are now full (though only 85% of theoretical maximum), and the transition from “free” to “user pays” is causing pain as software has to be upgraded and users proceed through the stages of mourning on free transactions (disbelief, denial, bargaining, guilt, anger, depression, and acceptance).

But other scalability issues exist: the bitcoin history has reached 100GB (that’s a lot of work for starting a new node), the size of unspent outputs each node has to remember keeps expanding (it must remember these forever), and the number of full nodes in the network is in long-term decline (though currently flat).

What’s Being Done For Scalability

There are several “20% improvement” factors on the horizon, and together they multiply to give significant improvements in scalability as software improves. Rising fees are causing wallet authors to (finally!) begin optimizing their transactions, because users are noticing.

Block propagation has gotten better (see centralization above) and slightly less coupled to blocksize, and validation has gotten much faster (thanks much to libsecp256k1) which may see us close the gap between the theoretical 1MB blocksize and the current 850k average blocksize.

Segregated Witness should increase blocks to about 2MB, though it depends how quickly the ecosystem (wallets and other transaction businesses) start using it.

Segregated witness makes signatures (aka “witnesses”) discardable, and gives them a discount over parts of transactions which must be kept (ie. unspent outputs). This should bias wallets towards using it so more of the blocks can be discarded by nodes.

Replace-by-fee is becoming more common: this allows you to bump the fee on transactions which are taking too long to confirm. This not only means you can be more aggressive on lowering fees, it also allows you to combine multiple payments into one if you have them, which reduces your total transaction size.

On the horizon are Schnorr signatures, which can be combined together, reducing witness size even further: instead of a transaction with two inputs which are each a 33 byte key and 72 byte signature, we might have two 33 byte keys, and a single signature. Interestingly, this also provides an incentive to adopt mixing protocols (like TumbleBit) because they are smaller and hence cheaper, helping the network fungibility even if you don’t care about fungibility yourself.

Finally, there are at two significant efforts to create off-chain scaling for bitcoins; Lightning for microtransactions, and the proposed sidechain MimbleWimble. Lightning takes Satoshi’s original (but incomplete) ideas for payment channels on top of bitcoin and makes them bi-directional and trustless, and forms them into a network. There are at least four teams of us actively working on implementing it. MimbleWimble is more radical, and uses a cut-down scriptless bitcoin with some amazing math to produce a blockchain which doesn’t require transmission or storage of any historical state, just the current unspent outputs, without loss of security (but with great fungibility benefits). Implemented as a sidechain, you would move bitcoins across to it, then back. It has cast its spell on Andrew Poelstra and I look forward to seeing an alpha release this year.


It’s often hard to find an overview of all the different threads of development and effort going on at once in the bitcoin technical community. I haven’t even covered more speculative things like Bitcoin-NG or Confidential Transactions nor developments which don’t directly address these three areas such as covenants or new scripting enhancements, let alone things which will no doubt be dropped from the sky

But hopefully this gives you a list of things I’m looking forward to in 2017!

About the Author 

This article was written by Rusty Russell. Rusty is a Linux kernel dev who wandered into Blockstream, and is currently trying to produce a prototype and spec for bitcoin lightning.


Lessons Learnt from The Lean Startup



The Lean Startup book authored by Eric Ries has been sitting on my shelf for quite sometime now, so since I am currently contributing to the making of a startup I figured I’ll take a look into it.

The book is divided into 3 parts, after reading the first two I had my mind blown with the pragmatic and scientific approach to building startups that is described in the book.

In this post, I would like to share some important insights that I gained regarding building highly innovative businesses.

Validating Value Proposition And Growth Strategy Is The Priority

Usually, a highly innovative startup company is working in its most early stage at building a product or a service that will create a new market.

Consumers or businesses have not been yet exposed to something similar to what is going to be built by the startup. Therefore the absolute priority for startups in early stage is to validated their value proposition i.e. to get real data about eventual customers interest regarding their product/service.

The other priority is to validate that the growth strategy that is going to be executed is, in fact, effective.

The growth strategy of a startup is its plan to acquire more and more customers in the long term and in a sustainable fashion.

Three kinds of growth strategies are described in the book:

  • paid growth in which you rely on the fact that the customers are going to be charged for the product or service, the cash earned from early users is reinvested in acquiring new users via advertising for example
  • viral growth in which you rely on the fact that customers are going to bring customers as a side effect of using the product/service
  • sticky growth in which you rely on the fact that the customers are going to use the service in some regular fashion, paying for the service each time (via subscription for example).

These growth strategies are sustainable in the sense that they do not require continuous large capital investments or publicity stunts.

It is important to know as soon as possible which strategy or combination of strategies is the most effective at driving growth.

Applying The Scientific Method

The scientific method is a set of techniques that helps us figure out correct stuff. After making some observations regarding a phenomenon, you formulate a hypothesis about that phenomenon.

The hypothesis is an assumption that needs to be proven correct or incorrect. You then design experimentations that are going to challenge the assumption.

The results of the experimentations makes the correctness or incorrectness of the hypothesisclear allowing us to make judgments about its validity.

In the lean startup methodology, your job as an entrepreneur is to formulate two hypothesis:

  • hypothesis of value (assumptions about your value proposition)
  • hypothesis of growth (assumptions about the effectiveness of the growth strategy)

These hypothesis are then validated/invalidated through experimentation. Following the precepts of lean manufacturing, the lean startup methodology prescribes to make experimentations while minimizing/eliminating waste.

In other words, you have to burn minimum cash, effort and time when running experiments.

An experimentation in the lean startup sense is usually an actual product/service and helps startups in early stage learn invaluable things about their eventual future market.

Sometimes startups learn that nobody wants their product/service, imagine spending 8 months worth of engineering, design and promotion work (not to mention cash) in a product/service only to discover that it does not provide value to anyone.

Minimum Viable Products And Feedback

As we pointed out earlier, an experimentation can be an actual product or service and is called the minimum viable product(MVP).

The MVP is built to contain just enough features to validate the value and growth hypotheses, effectively requiring minimum time, effort and cash.

By getting the MVP launched and in front of real users, entrepreneurs can get concrete feedback from them either directly by asking them (in focus groups for example) or via usage analytics.

Analytics scales better then directly talking to customers but the latter is nonetheless used to cross validate results from the former.

It is crucial to focus on metrics that creates fine grained visibility about the performance of the business when building(or using) a usage analytics system. These metrics are called actionable metrics because they can link causes and effects clearly allowing entrepreneurs to understand the consequences of ideally each action executed. Cohort analysis is an example of a analytics strategy that focuses on actionable metrics.

The bad kind of metrics are called vanity metrics, these tend to hide how the business is performing, gross numbers like total users count are an example of vanity metrics.

The author cites several examples of different startups that managed to validate or debunk their early assumption by building stripped down and non scalable MVPs and even sometimes by not building software at all.

You would be surprised to hear for example how the Dropbox folks in their early stage managed to created a ~4 minute video demonstrating their product while it was still in development. The video allowed them to get more people signed up in their beta waiting list and raise capital more easily.

Closing Thoughts

In the first two parts of the book, the author talks also about how employees inside big companies working on highly innovative products and services can benefit greatly from the lean startup approach, although very interesting this is not very useful for me right now.

The third part, talks about the challenges that arises when the startup gets big and starts to stabilize and how to address them. Basically it revolves around not loosing the innovative spirit of the early days, again, this is not very useful for me so maybe for good future reading.


About the Author

This article was produced by Tech Dominator. see more.

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Women on Top in Tech – Dr. Sanna Gaspard, Founder and CEO of Rubitection



(Women on Top in Tech is a series about Women Founders, CEOs, and Leaders in technology. It aims to amplify and bring to the fore diversity in leadership in technology.)

Dr. Sanna Gaspard is the Founder and CEO of Rubitection, a medical device start-up developing a diagnostic tool for early stage pressure detection, assessment, and management. She is an Entrepreneur, inventor, and biomedical engineer with a passion for innovation, entrepreneurship, healthcare and medical devices. She has received recognition and awards including being selected as a finalist for the Cartier Women’s Initiative Awards(’13), a semi-finalist for the Big C competition (’14), a finalist for the Mass Challenge Business accelerator in Boston, and taking 1st place at the 3 Rivers Investment Venture Fair’s Technology showcase (‘11). Her vision is to make the Rubitect Assessment System the global standard solution for early bedsore detection and management.

What makes you do what you do? 
I am driven to have impact and improve healthcare as I have a strong drive to problem solve, comes up with new ideas, and see them come to life.

How did you rise in the industry you are in? 
I first focused on getting the educational background and then I pursued the goals I have for myself. I got my PhD in Biomedical Engineering with a specialization in medical device development. Having the educational background is important as a woman and minority to assist people in taking your seriously.  After completing my PhD, I focused on bringing my invention for a medical device for early bedsore detection and prevention called the Rubitect Assessment System to market to help save lives and improve care.

Why did you take on this role/start this startup especially since this is perhaps a stretch or challenge for you (or viewed as one since you are not the usual leadership demographics)?
I started my startup, Rubitection , because I felt it was the best way to bring the technology to market. I knew that if I did not try to commercialize the technology, it would not make it to the doctors and nurses. I also have confidence that I could manage developing the technology since I had taken classes on entrepreneurship and had my PhD in biomedical engineering with a specialization in medical devices.

Do you have a mentor that you look up to in your industries or did you look for one or how did that work? How did you make a match if you did, and how did you end up being mentored by him/her?
No, I don’t have a specific mentor in my field. I am looking for one at the moment. However, I do look up to Steve Jobs and Oprah as examples of how one can start with nothing and work their way up and build a successful, global, and reputable business and brand.

Now as a leader how do you spot, develop, keep, grow and support your talent?  
I first try to find people who have fundamental technical or work experience to be competent to complete the work. I then evaluate the person for intangible skills like independent thinking, reliability, leadership, resilience, organizational skills, strong work ethic, open mindedness/flexibility, and good communication skills.

Do you consciously or unconsciously support diversity and why? 
I consciously make an effort as a minority woman in tech, I intimately understand the need to promote diversity within my business and outside my business. I first hire the best people for the job and also make a point to hire women and minorities qualified for the position.

What is your take on what it takes to be a great leader in your industry and as a general rule of thumb?  
It takes resilience, vision, being a team player, an ability to inspire others and delegate work, knowing your weakness, and knowing when to put your business or yourself first.

Advice for others?
My advice to others is to take calculated risks, pursue every opportunity, surround yourself with supporters, build your team with smart dedicated people, and stay focused on your vision. I am striving to implement this advice myself as I work towards commercializing my technology for early bedsore detection, grow my team, and recruit clinical partners to address an $11 billion US healthcare problem which affects millions around the world.

If anyone is interested in learning more about our work or company, please contact us at [email protected].

To learn more about Dr. Sanna Gaspard, CEO of Rubitection visit:

If you’d like to get in touch with Dr. Sanna Gaspard, please feel free to reach out to her on LinkedIn:

To learn more about Rubitection, please click here.

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