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Blockchain Demo

A web-based demonstration of blockchain concepts.

Blockchain 101 - Demo

This is a very basic visual introduction to the concepts behind a blockchain. We introduce the idea of an immutable ledger using an interactive web demo that is available here:


Get the code:

git clone

Install dependencies:

cd blockchain-demo
npm install

Run the server:

npm start



#For windows: if the above command didn't work, use this (make sure you have Node.js installed in your system):

node ./bin/www      

Point a web browser at the demo:


Setup using Docker

Get the code:

git clone

Run the Docker setup:

cd blockchain-demo
docker-compose up -d

Point a web browser at the demo:


Optional Configuration

You can adjust the "number of zeros" required by the demo by editing the first two lines of public/javascripts/blockchain.js.

Because there are 16 possible characters in a hex value, each time you increment the difficulty by one you make the puzzle 16 times harder. In my testing, a difficulty of 6 requires a maximumNonce well over 500,000,000.

If you adjust the difficulty above 4, blocks will show up as not mined because the demo data assumes 4 zeros for a signed block. For example, on the http://localhost:3000/block page with a difficulty of 6, the first nonce that works is 8719932 yielding a hash of 000000669445c22167511857d8f3b822b331c3342f25dfdcb326e35c1a7aa267. This gets out of hand fairly quickly though. Here's some time estimates at the various thresholds.

digits nonce time estimate
4 500,000 15 minutes
5 8,000,000 4 hours
6 128,000,000 3 days
7 2,048,000,000 a month
8 32,768,000,000 2 years
9 524,288,000,000 30 years
10 8,388,608,000,000 481 years
11 134,217,728,000,000 7,690 years
12 2,147,483,648,000,000 123,036 years
13 34,359,738,368,000,000 1,968,581 years
14 549,755,813,888,000,000 31,497,291 years
15 8,796,093,022,208,000,000 503,956,662 years

In the production bitcoin blockchain, block 458,091 has the hash digest 00000000000000000000011246f099d94f91628d71c9d75ad2f9a06e2beb7e92. That's 21 zeros in a row! That one block would take this software approximately 8,454,989,768,407,765 years to mine.

Public Private Key Demo

The 2nd part of the 101 session:

Send Thanks

Bitcoin gratefully accepted: 1K3NvcuZzVTueHW1qhkG2Cm3viRkh2EXJp