# Blockchain Demo A web-based demonstration of blockchain concepts. [](https://www.youtube.com/watch?v=_160oMzblY8) 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: http://andersbrownworth.com/blockchain/ ## Setup Get the code: ``` git clone https://github.com/anders94/blockchain-demo.git ``` Install dependencies: ``` cd blockchain-demo npm install ``` Run the server: ``` npm start ``` OR ``` ./bin/www ``` #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: ``` http://localhost:3000 ``` ## Setup using Docker Get the code: ``` git clone https://github.com/anders94/blockchain-demo.git ``` Run the Docker setup: ``` cd blockchain-demo docker-compose up -d ``` Point a web browser at the demo: ``` http://localhost:3000 ``` ## 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: * https://github.com/anders94/public-private-key-demo ## Send Thanks  Bitcoin gratefully accepted: `1K3NvcuZzVTueHW1qhkG2Cm3viRkh2EXJp`