Blockchain

The present definition of block chain is the one referred to the Bitcoin technology developed by Satoshi Nakamoto, in which the block chain is an integral part of it; unlike the new term 'blockchain' introduced by different companies and authors to refer to Bitcoin technology as a whole.

A chain of blocks (block chain), also known as distributed ledger (distributed ledger), is a distributed database that registers blocks of information and interlaces them to facilitate the recovery of information and the verification that it has not been changed. The blocks of information are linked by means of hash pointers that connect the current block with the previous block and so on until the block genesis is reached.

The chain of blocks is stored by all those nodes in the network that stay in sync with it.

Each block belonging to the block chain contains information regarding the transactions related to a period (grouped in a structure called Merkle Tree), the cryptographic address (hash pointer) of the previous block and a unique arbitrary number (nonce).

HASH CRYPTOGRAPHIC FUNCTION

The information contained in each block is registered in the form of a cryptographic hash, which allows easy verification, but makes it impossible to recreate the input data. Bitcoin uses the SHA-256 cryptographic hash function which implies that its hash pointers are of a fixed size of 256 bits.

A hash function is any function that can be used to map data from an arbitrary size to fixed-size data in a reasonable amount of time. The values ​​generated by a hash function are called hash values, hash codes or simply hash.

FUNCTION MERKLE TREE

The transactions or data are recorded in each block of the block chain in a cryptographic structure of hash pointers called the Merkle tree, due to its inventor Ralph Merkle. This structure groups the blocks of information in pairs and generates a hash for each block of data. Then, the generated hashes are again grouped in pairs and generate a new hash that in turn is grouped with another and repeated way up the tree until reaching a single block, the root of the tree, which is called root hash pointer (root hash) and registers in the address of the current block (block hash) in order to reduce the space occupied by each block.

In addition, this hash pointer structure allows you to go through any point in the tree to verify that the data has not been manipulated, since, as with the chain of blocks, if someone manipulates a block of data in the lower part of the tree, it will that the hash pointer that is one level higher does not match, and even if you continue to manipulate this block, the change will eventually propagate to the top of the tree where you will not be able to manipulate the hash pointer that we have stored because it belongs to another structure (block chain) in which a hash has also been generated using the root hash as input. So, again, any attempt to manipulate any piece of data will be detected just by registering the hash pointer at the top.

NONCE

In cryptography, the term nonce is used to refer to a value that can only be used once. This unique number or nonce, is a random number issued by the miners through the Work Test (PoW) that serves to authenticate the current block and prevent the information from being reused or changed without doing all the work again.