README.md

Blockchain-demo 'josokwCoin'

This code example shows how I try to learn to write a C++ Blockchain demo version for educational purposes. I use a 'learning by cloning' approach: refactoring JavaScript code examples to C++.

JavaScript code examples Savjee:

• Creating a blockchain with Javascript (Blockchain, part 1), C++ release v0.1
• Implementing Proof-of-Work in Javascript (Blockchain, part 2), C++ release v0.2
• Miner rewards & transactions in Javascript (Blockchain, part 3), C++ release v0.3
• Signing transactions in Javascript (Blockchain, part 4)

Build management by CMake

CMake must be installed. Goto the Blockchain-demo directory.

mkdir build
cd build
cmake ..
make

SHA-256

SHA: Secure Hash Algorithm. SHA-256 is part of SHA-2 set of cryptographic hash functions, designed by the U.S. National Security Agency (NSA) and published in 2001. The SHA-2 family consists of six hash functions with digests (hash values) that are 224, 256, 384 or 512 bits: SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, SHA-512/256.

Some examples hashing strings:

"1"      ==> 6b86b273ff34fce19d6b804eff5a3f5747ada4eaa22f1d49c01e52ddb7875b4b
"12"     ==> 6b51d431df5d7f141cbececcf79edf3dd861c3b4069f0b11661a3eefacbba918
"123"    ==> a665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3
"321"    ==> 8d23cf6c86e834a7aa6eded54c26ce2bb2e74903538c61bdd5d2197997ab2f72
"abc321" ==> 95d0bf701b3efa5fe1207167d08044bac7ae34c090af18847c915c5c8a49455a
"     "  ==> 399141be1d30ac2656d89eedcf0d8dcedaa72d6c29bf959cae243dc7b1442cf6
"abc"    ==> ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad

Online hash generator.

How secure is 256 bit security?

Executing 'Blockchain-demo' and mining

The executable is found in the bin directory. The default difficulty level for mining is 4.

cd ../bin
./Blockchain-demo

Proof of work (POW): a method to insure that the new block was difficult (costly, time consuming) to be made. The hash of a block must start with a certain number of zeros.

The nonce in a bitcoin block is a 32-bit (4-byte) field whose value is set so that the hash of the block will contain a run of leading zeros.

The difficulty level for mining can be changed by a command line parameter.

cd ../bin
./Blockchain-demo 3

Bitcoin: critique and problems ==> IOTA

• Huge amount of powerconsumption for mining.

• Scalability problem.

• The IOTA Tangle takes another approach: no blocks, no chain (Directed Acyclic Graph).

• Industrial IoT A Smart Factory Powered by an IOTA.

Output example

Output in JSON format for difficulty level 4:

BlockchainDemo v0.3.0

Starting the miner...
Block mined: 0000bb9a29f319d928ee4a1644ede1ca77969bad2368a5380bbc25e05669dc44

Blockchain JSON:
{
"chain": [
    {
        "hash": "a18993cf60a314d0c460c8b014ffe3d67fe2bcf4b09d4f5cea14e5259991b703",
        "nonce": 0,
        "previousHash": "0",
        "timestamp": "2019/01/04-10.26.54"
    },
    {
        "hash": "0000bb9a29f319d928ee4a1644ede1ca77969bad2368a5380bbc25e05669dc44",
        "nonce": 1464,
        "previousHash": "a18993cf60a314d0c460c8b014ffe3d67fe2bcf4b09d4f5cea14e5259991b703",
        "timestamp": "2019/01/04-10.26.54",
        "transactions": [
            {
            "amount": 100,
            "fromAddress": "address1",
            "timestamp": "2019/01/04-10.26.54",
            "toAddress": "address2"
            },
            {
            "amount": 50,
            "fromAddress": "address2",
            "timestamp": "2019/01/04-10.26.54",
            "toAddress": "address1"
            }
        ]
    }
],
"length": 2,
"pendingTransactions": [
    {
        "amount": 100,
        "fromAddress": "",
        "timestamp": "2019/01/04-10.26.54",
        "toAddress": "josokw-address"
    }
]
}

Balance 'josokw' is 0

Starting the miner again...
Block mined: 00001623918c0e568ea6fd5d0717bb9ecc0eef0ad9b185fe218141c72fd294c5

Blockchain JSON:
{
"chain": [
    {
        "hash": "a18993cf60a314d0c460c8b014ffe3d67fe2bcf4b09d4f5cea14e5259991b703",
        "nonce": 0,
        "previousHash": "0",
        "timestamp": "2019/01/04-10.26.54"
    },
    {
        "hash": "0000bb9a29f319d928ee4a1644ede1ca77969bad2368a5380bbc25e05669dc44",
        "nonce": 1464,
        "previousHash": "a18993cf60a314d0c460c8b014ffe3d67fe2bcf4b09d4f5cea14e5259991b703",
        "timestamp": "2019/01/04-10.26.54",
        "transactions": [
            {
            "amount": 100,
            "fromAddress": "address1",
            "timestamp": "2019/01/04-10.26.54",
            "toAddress": "address2"
            },
            {
            "amount": 50,
            "fromAddress": "address2",
            "timestamp": "2019/01/04-10.26.54",
            "toAddress": "address1"
            }
        ]
    },
    {
        "hash": "00001623918c0e568ea6fd5d0717bb9ecc0eef0ad9b185fe218141c72fd294c5",
        "nonce": 41362,
        "previousHash": "0000bb9a29f319d928ee4a1644ede1ca77969bad2368a5380bbc25e05669dc44",
        "timestamp": "2019/01/04-10.26.54",
        "transactions": [
            {
            "amount": 100,
            "fromAddress": "",
            "timestamp": "2019/01/04-10.26.54",
            "toAddress": "josokw-address"
            }
        ]
    }
],
"length": 3,
"pendingTransactions": [
    {
        "amount": 100,
        "fromAddress": "",
        "timestamp": "2019/01/04-10.26.54",
        "toAddress": "josokw-address"
    }
]
}

Balance 'josokw' is 100

The josokwCoin blockchain is valid