Understanding Blockchain: What is a Hash?

A hash is a one way function that transforms a string of data of arbitrary size to a bit string of a fixed size. This function has the following properties:

  1. It is quick
  2. It is impossible to figure out the original string of data from the hash. (except by brute force, trying all possible input strings until we obtain the same hash)
  3. Two different inputs will always produce different outputs
  4. A small change to the input string changes the output radically
  5. Same input always produces same output.

Hash is useful for example when you want to make sure that a file that you have downloaded is the file that the owner of the file intended for you to download and it has not been modified in transit.

For example, you want to download notepad++ so you go to the website and click on the link to download the Notepad++ Installer. A file downloads, but, how do you know the file hasn’t been corrupted or somehow modified while downloading?


You can check if the hash of the file you downloaded is the same hash that the owner of the website indicates. If you click on the link called “Sha-1 digests for binary packages”


You can see the SHA-1 hash (there are many hash functions, SHA-1, MD5, SHA-256…) of the file should be 6a54e0e8c8dbfca68abe3cbe66d99c66ced59cea


You can now use any SHA-1 hash calculator to chech that the file you have downloaded matches the hash that should be. This would indicate that the bits of this file are exactly the same bits as of the file that the website owner put on the website for download. If we change even 1 bit, the hash would be completely different.

If you have a linux computer you can use command sha1sum and you can see that the resulting hash is exactly the same one. You don’t need to go character by character checking, since if the file had been altered, the result would be wildly different.


If you don’t have a linux command line you can use an online sha1 calculator to see that with the same input, the SHA-1 function will return the same hash, no matter in which platform or computer you execute the function.


Hash functions are used everywhere when we need to check that a file or string of bits matches what we expect. For example VLC player uses hash to look for subtitles to the movie you are playing. Linux uses hash to check that the password you have entered matches the password hash that is stored in the hard drive. This ensures that if someone hacks into the computer, and obtains the passwords file, there is no function that can obtain the original password from the hash, since hash is only one way, but at the same time it’s trivial for the operating system to verify if the password you have entered is correct (since it will produce the same hash as the one stored in the hard drive).

Hash is a key piece of the blockchain algorithm. Since I intend to disect the blockchain algorithm to explain it piece by piece, it’s important that the basic pieces are well understood.



What is Fintech?

Fintech is short for “Financial Technology” and covers all technologies applied to finance. It is used mainly to refer to disruptive innovations in the Financial industry which is a topic that’s getting a lot of traction, specially since in 2008 Satoshi Nakamoto published his 9 page paper on bitcoin. However, many of these fintech disruptions don’t necessarily come from new technologies, just new ways of using existing technology.

One way fintech disruption can be classified is

  1. Infrastructure: Technical Innovations to infrastructure are necessary to solve business problems and enable disruption.
    1. Identity: One of the big concerns of regulators is KYC (Know your customer). In an online world, what can be done to ensure that a person is who he claims to be? With the concept of wallets which are anonymous, what can be done to ensure money movements can be associated with their owners? This is important to avoid money laundering, financing of terrorism, tax evasion…
    2. Privacy: On the other end of the spectrum of KYC, privacy is also important for end users. MIT are working on Enigma which is a blockchain based, distributed computer similar to Ethereum but with a focus on solving the millionaire’s problem (two millionaires want to know who of them is richer without disclosing their wealth) and allow calculations to be performed by the nodes without disclosing the data (but only pieces of the data which do not give a vision regarding the whole)
    3. Security: If all my bitcoins are sitting in my bitcoin wallet, which is a file in my computer and I lose my file, or forget my password, all my bitcoins are gone forever. If a hacker was able to copy my wallet, which is just a normal file, and was able to find out my password (for example hacking my keepass by compromising my computer) he could transfer all my bitcoins to his wallet and I would have lost them forever.
  2. Money and Payments: Mankind has come a long way from the cash only world where currency was backed by precious metals. Plastic credit and debit cards are the current norm. Paypal, near touch payments with mobile devices are trying to become mainstream, but a big disrupting technology has emerged in 2008: The Blockchain. The Blockchain enables:
    1. peer to peer payments:
      1. Until now when Alice wanted to send Bob money remotely, the only way to do this was to go through a trusted intermediary (a bank, a remittance company, paypal…). With blockchains like the one used by Bitcoin or Ethereum Alice can pay Bob directly, with no intermediary, and more importantly almost no fees. This will radically improve the lives of people who try to send money back to their families in developed countries, for which they need to pay exorbitant fees, wait in line and hope that the money is not lost, while at the other end of the transaction, the recipient has to go through a similarly daunting process.
      2. The peers in a transaction don’t neccesarily need to be human. M2M (Machine to machine) payments is something that can be feasible. For example slock.it is building locks that will open if a smart contract tells them to open.
    2. Cryptographically guarantee that a record can not be modified
      1. Entries in the blockchain cannot be modified. The older an entry is the more time it would take an attacker to be able to forge an alternative chain. Thanks to proof of work, we can rest assured that an attack is not possible. I’ll go deeper into these fun techie ideas in future posts.
    3. smart contracts
      1. Smart contracts enable programs to be run on the blockchain allowing these programs to send payments automatically if certain conditions are met (for example Alice could bet with Bob on the outcome of a match. The smart contract could check for the result of the match and transfer the money from Alice to Bob automatically once the result is known)
    4. immediate settlement
      1. Currently in capital markets, settlement is done two or three days after the trade is done due to the complex legacy infrastructure that it must go through. With blockchain, the transaction could be settled in minutes instead of days.
    5. No settlement risk
      1. Since transactions are atomic, the transaction either gets done or it does not. Hence there would be no settlement risk. However there are some views that claim that a blockchain can never really finalise a transaction as it is theoretically possible that due to the way the consensus algorithm works, the latest blocks may be rolled back. Vitalik Buterin, founder of the Ethereum foundation argues that by that same logic, the current system can also never really finalise a settlement, since the registry could be burnt down or defaced by a malicious user.
  3. Capital Markets:
    1. In the capital markets space, disruptive technologies are emerging in the form of:
      1. Robo-Advisors: Artificial Intelligence is enabling automated investment advice. For example Betterment.com,  Robinhood.com or Wealthfront.com offer this service
      2. Equity crowdfunding: A trend towards equity crowdfunding is emerging where shares in the company would be acquired by the crowdfunders, an example of this is Fundersclub.com or equitynet.com
      3. Blockchain driven markets: Digital Asset Holdings is a very strong startup, aiming at creating a market which is settled over a blockchain. Many strong incumbents are backing this initiative which looks very promising. This platform would deliver on the promise of instant settlement. Ethereum and Digital Asset Holdings are the two fintech disruptors which interest me the most.
  4. Marketplaces:
    1. SME lending companies such as Bond Street, On Deck, or Funding Circle are enabling investors to fund SMEs without SMEs needing to ask a bank
    2. Banking the unbanked: Mpesa is a vodafone initiative which allows people in developing countries to send and receive money from their cellphones via PIN protected SMS. Users can recharge their accounts through airtime resellers and retail outlets playing the role of banking agents.
    3. Credit ratings for the unbanked: companies like First Access are allowing individuals and SME in developing countries to obtain a credit rating when applying for a loan at a bank. First Access gain permission from the client to acquire his cellphone payment history from his cellphone provider, with this history of payments they can give the bank a credit rating for a direct loan.