Blockchain Academy
We'll get together for networking with people interested in Blockchain including developers and anyone curious about Blockchain.

Hash

A hash function is any function that can be used to map data of arbitrary size onto data of a fixed size. Since it works in one-way function, it is hard to find out the original value with the value calculated in the function. The values returned by a hash function are called hash values, hash codes, or simply hashes. Hash has been used even before the blockchain for fast data search and encryption.

The core quality of Hash function is which if the original value changed, the value returned would be completely different. This is called the 'determinism'.

And with this, the validity of transaction and block is verified through comparing the hash value. If the information in transaction has been forged even for a little, the change will show on the original data, since the returned value will be different with hash function determinism. Also, it is easy to find a target data through Merkle tree, which is a hash tree, and it is used when making public key from private key. (Bitcoin adopts SHA256 algorithm and Ethereum adopts keccak256 algorithm.) By inputting hash of data, which enters the block, it is possible to secure the block size. As such, the hash algorithm is playing various roles in the blockchain that it is one of the most important technologies to make blockchain possible.