Blockchain is a distributed ledger that uses various forms of cryptography to digitally sign blocks of data to ensure the integrity of the data. There are two main technologies in a typical blockchain implementation; distributed ledger and cryptography. The different implementation might add to this but this is the basic technology stack for blockchain. Distributed Ledger A distributed ledger database is really the core value of a blockchain technology implementation. It is basically storing a series of transactions in a way where the hash or cryptographical signature or the previous transaction is used to encrypt the next transaction. The combination of the hash from the previous transaction and the current transaction provide unique ‘blocks’ of data that only mathematically make sense in the order they were created and stored. There are variations to distributed ledger technology such as if it is private or public, what type of hash is used, is there a ‘work’ mechanism and what type of peer to peer networking is implemented, but this series of blocks that have a hash-based integrity mechanism is the core of distributed ledger technology. Cryptography There are many types of cryptography. Typically, for the majority of popular blockchain implementations, hashes and public key cryptography are used to ensure distributed ledger integrity. For example, Bitcoin uses SHA-256 to determine the hashcash cost in blocks before they are created. Hashcash cost is a method of slowing down the cryptographical discovery which in Bitcoin provides the award or the actual Bitcoin. There are often other technologies used in blockchain implementations such as Proof Of Work protocol but this is typically only in public systems. Proof of Stake systems are found in private implementations. The data and the type of hashing vary as well but if you understand the distributed ledger and the cryptography of hashing then you will understand how these variations only go to serve the above-mentioned technologies used in blockchain.