Blockchain is an open distributed ledger resistant to modification of its records, i.e. `blocks.’
Cryptography serves to secure and link them in a `chain;’ a block usually contains a cryptographic hash of the previous block, a timestamp and transaction data.
The authentication of a record is achieved by mass collaboration of agents with one another in a blockchain network and driven by collective self-interests.

Blockchain characteristics include high Byzantine fault tolerance and security by design.
The retroactive alteration of a block requires to edit the data in all subsequent blocks accordingly.
Therefore, for such operations a collusion of the network majority is necessary.

As its applications became increasingly popular, `blockchain’ …show more content…
While the constraints of blockchain or DAG have not represented a major limitation for any of its widely popularised real-life applications, the adequacy of specific solutions have been contested.

Precisely this has led to the development of various blockchain and DAG technologies.
The most often criticised characteristics of blockchain are the cost of transaction validation, latency, and potential scalability issues; furthermore, the block size and data storage requirements grow rapidly as a function of network activity over time.
DAG flows, on the other hand, include potential problems with consensus algorithms and the traceability of the history of particular blocks.

Blockchains---both strictly blockchain-based and those using DAGs---are often associated with cryptocurrencies.
The first widely known application of a cryptographically secured chain of blocks using Merkle trees to group several transactions together and resistant to Sybil attacks was Bitcoin (BTC), conceptualised in …show more content…
In RTXP, the validation of a transaction, either in a fiat currency or Ripple's internal currency (XRP), depends on the consensus of a supermajority of the nodes from a Unique Node List (UNL); uniqueness means that different nodes are belong to different and mutually independent parties.

From 2013, the creators of the blockchain-based distributed computing platform Ethereum have explored complementary features of the technology and, in 2014, launched the fundamental value token within the platform, Ether (ETH).
Initial coin offering (ICO) has since become a common practice among the creators of new blockchain technologies as it represented a potential to directly monetise their inventions.
Especially so, if they choose to offer their technologies as open-source software instead of protecting them with legally enforceable patents.
While the open-source model, encouraging collaboration and the popularisation of a technology, may be regarded as the standard, restricting access rights remains an option, explored e.g. by the inventors of