Cryptography

The most popular use of blockchain is to create a cryptocurrency. As the word crypto is in cryptocurrency, you would expect that you need to master cryptography in order to become a blockchain programmer. That is not true. You only need to know two things about cryptography:

• Private key and public key (asymmetric cryptography)
• Hashing

These two have been explained in the previous part of this chapter. You don't need to know how to design a hashing algorithm or private key and public key algorithm. You only need to get an intuitive understanding of how they work and the implications of these technologies.

The implication of private keys and public keys is that it enables decentralized accounts. In a normal application, you have a username and password. These two fields enable someone to access their account. But having a private key and public key enables someone to have an account in a decentralized manner.

For hashing, it is a one-way function, meaning that given an input, you can get the output easily. But given an output, you couldn't get the input. A simple version of a one-way function would be this:

This is an addition process. If I tell you one of the outputs of this function is 999, and I ask you what the inputs are, you couldn't guess the answer. It could be anything from 1 and 998 to 500 and 499. A hashing function is something like that. The algorithm is clear as sky (you can read the algorithm of any hashing function on the internet), but it's hard to reverse the algorithm.

So, all you need to know about hashing is this: given input input you get this SHA-256 output (in hexadecimal): c96c6d5be8d08a12e7b5cdc1b207fa6b2430974c86803d8891675e76fd992c20. If you don't know the input, you couldn't get the input based on this output alone. Say you know the input input it is very prohibitive to find another input that produces the same output. We wouldn't even know whether such input exists or not.

That is all you need to know about cryptography when you become a blockchain developer. But that's only true if you become a certain type of blockchain developer, who creates a program on top of Ethereum.