Appendix A. Terms and Theory

Distributed architecture – software and network architecture design approach, where each user node is connected to others, aimed to bring (through one-rank connections) stability and high fault tolerance to the network.

Directed acyclic graph – finite directed graph with no directed cycles. DAG is a directed graph that has a topological ordering, a sequence of the vertices such that every edge is directed from earlier to later in the sequence. DAGs allow for multiple chains of blocks to co-exist and interconnect while never forming an edge with a parent node. Nodes can exist in parallel, as long as information is directed in the same way. There are no blocks in DAG-based chains, each node is transaction.

Blockchain – organized directed database, bound by cryptography and Merkle tree data structure. By design, a blockchain is resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way". For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for inter-node communication and validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without alteration of all subsequent blocks, which requires consensus of the network majority. Although blockchain records are not unalterable, blockchains may be considered secure by design and exemplify a distributed computing system with high Byzantine fault tolerance. Decentralized consensus has therefore been claimed with a blockchain.

Merkle tree – a tree in which every leaf node is labelled with the cryptographic hash of a data block, and every non-leaf node is labelled with the cryptographic hash of the labels of its child nodes. Hash trees allow efficient and secure verification of the contents of large data structures.

Actor – an acting unit of network, that:

1. Has “public-private” key pair;

2. Is verified by other network actors;

3. Can send and receive transactions;

4. Can load data into network;

Actor entities examples: user, smart contract, bot etc.

Proof-of-Existence – a concept aimed to verify existence of real world object or digital unit via digital algorithms or systems (like blockchain). This concept is used to:

• secure the ownership of real-life and digital entities;

• protect property rights;

• prove the existence of selected entities;

• allow fast and decentralized verification of all named above

Non-fungible token (NFT) is a unit of data on a digital ledger called a blockchain, where each NFT can represent a unique digital item, and thus they are not interchangeable. NFTs can represent digital files such as art, audio, videos, items in video games and other forms of creative work.

Genesis Block – a blockchain unit that holds state of blockchain. Bitcoin- and Ethereum-like blockchains have Genesis Blocks as initial blocks of chain, holding initial addresses and their balances.

Fast-Blockchain mode – ExC operation mode, when device downloads only part of blockchain from current block to last Genesis Block. This mode is made for devices with hard limit of memory and users, who want to start network operation faster.

Full-Blockchain mode – ExC operation mode, when device downloads full blockchain. This mode requires more memory, but grants possibility to make faster checks during all prove algorithms.