# blockchain-documentation

This is a summary of the concepts around Blockchain technology!

1. There are two types of Software architectures exists - Centralized & Distributed
2. A Hybrid architecture is also possible Centrally Distributed architectures
3. Blockchain simply put is a tool to maintain Trust & Integrity in a peer-to-peer system
4. The challenge is to solve the Trust & Integrity in the worst of all situations

# The Blockchain challenge - The idea behind Mining or Proof-Of-Work:

Here is a very simplistic view of what the actual miners do when mining for the Bitcoin, or rather to put it in mathematical terms, solving a puzzle - The puzzle is always to find the leading zeros in the resulting hash of a new block. For example., take a look at the following function written in Scala:

 1def sha256Hash(text: String) : String = String.format("%064x", new java.math.BigInteger(1, java.security.MessageDigest.getInstance("SHA-256").digest(text.getBytes("UTF-8"))))
2
3@scala.annotation.tailrec
4def mineSomeShit(str: String, appender: String, difficulty: String): String = {
5  val hashed = sha256Hash(str)
6  println(hashed)
7  if (hashed.take(difficulty.length).startsWith(difficulty))
8   hashed
9  else {
10    val newString = str + appender
11    (mineSomeShit(newString, appender + appender, difficulty))
12  }
13}


We will hash the String "Hello" and see if the resulting hash contains a leading zero's (the difficulty we set). If we do not find the hash with the expected number of leading zeros (the difficulty we set) we will append the String "Hello" with 1 to the end and re-compute the hash and check if we have the needed number of leading zeros. So here our appender that we pass to the mineSomeShit method is the nonce!

1mineSomeShit("Hello", "1", "0")


See I'm setting the difficulty to single zero which is what I expect to see at the staring position of the resulting hash. If I find a match from the resulting hash, I return, but if not, I keep appending a 1 to the end of "Hello" and continue hashing the resulting new String. This way of adding arbitrary String in our case "1" in Bitcoin terms is called a nonce! So a test run on my Mac would look this:

 1scala> mineSomeShit("Hello", "1", "0")
2185f8db32271fe25f561a6fc938b2e264306ec304eda518007d1764826381969
3948edbe7ede5aa7423476ae29dcd7d61e7711a071aea0d83698377effa896525
57c01a6b99ca7d331c85b2f6826cf5c6429613d617ced1a761e36298de903c1a5
79e77cc0f3906d514f79889ec8d49b94488f82178fb368fef286b26f3964aa077
88e8a20333f0fc59553b7a14a269206688508e653f5058e891711eba61cd5df17
93740a40fb9b1f71f6e69b8268335aaf451b077c0ffe0df94d46c229175f21a16
10+ 0xc547c99864a134db0c95e459b885e34b5e3ecd70f134e574c593e7fb113ef3


So there we go! We found out the hash with a single leading zero - I solved this puzzle - I get a ShitCoin for my "Proof of Work". Let us now notch it up a little by setting the difficulty to finding 2 leading zeros in our resulting hash. A test run on my Mac is as below:

 1scala> mineSomeShit("Hello", "1", "00") // Setting the difficulty to two leading zeros
2185f8db32271fe25f561a6fc938b2e264306ec304eda518007d1764826381969
3948edbe7ede5aa7423476ae29dcd7d61e7711a071aea0d83698377effa896525
57c01a6b99ca7d331c85b2f6826cf5c6429613d617ced1a761e36298de903c1a5
79e77cc0f3906d514f79889ec8d49b94488f82178fb368fef286b26f3964aa077
88e8a20333f0fc59553b7a14a269206688508e653f5058e891711eba61cd5df17
93740a40fb9b1f71f6e69b8268335aaf451b077c0ffe0df94d46c229175f21a16
10+ 00c547c99864a134db0c95e459b885e34b5e3ecd70f134e574c593e7fb113ef3


Ok! I get another ShitCoin - Glad that I can do this with my Mac! Let us notch it up even higher, this time around, the puzzle to solve is to find a hash with 3 leading zeros - Guess what, my Mac could not handle it, the JVM could not handle it! Here it is:

 1scala> mineSomeShit("Hello", "1", "000") // I'm setting the difficulty to 3 leading zeros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.lang.OutOfMemoryError: Java heap space


This is exactly what happens when mining BitCoins. You need computational power as the difficulty goes higher and higher with every batch of Blocks! There is no other way to find the hash with leading zeros, other than doing a brute force trial and error by adjusting a portion of the input block and calculating hashes over and over again until one of the hashes fulfills the puzzle by chance. Well, finding a hash with leading zero's is one thing while setting a target on the found hash with leadin zeros is what makes the mining even harder!

Roughly every 14 days the Bitcoin difficulty is adjusted such that the time between successive blocks remains constant at 10 minutes.

The screenshot below shows the latest block info (as of 3-Nov-2017) from the Bitcoin network:

The puzzle is to find the hash with 18 leading zeros as it can be seen in the Hash! So you can imagine now why a Million dollar is needed to solve a single puzzle!

If you then look at the following URL, you can figure out the latest BlockInfo and from there you can figure out the difficulty that is current when mining a block!

https://blockchain.info/block

500 peta hashes per second is produced by the Blockchain network. The average of 10 minutes (time taken to mine a single block) is maintained dynamically by the Blockchain network!

SHA256 is just about flipping bits - flipping bits need energy - heat - with the heat generated from this hardware, I can heat my household, toast a bread, this hardware is specifically designed to do hashes - If you do not cool them they melt! - Doing this in Chennai, my hometown which never has Winter, would not be economical!

While at it, I wanted to create a simple private ethereum network, and I did manage to do it and run them as Docker container's. I just ran two nodes on my Mac and I never saw my battery draining so fast! These Blockchain networks are certainly power thirsty! Take a look here for the Demo: https://github.com/joesan/lab-chain

Apart from this, if you can grasp the ideas behind the following topics, you have understood somewhat technically what Blockchain is and how it works in the Bitcoin setup.

1. Transactions
2. Difficulty
3. Hash
4. Nonce
5. Double Spending Problem
6. Byzantine General's problem

You can find more details on the above mentioned topics at this page: https://en.bitcoin.it/wiki/Main_Page