# Distributed Ledger Technology Review and Decentralized Applications Development Guidelines
## 2 Protocol and Network Tier
### Network Layer
#### 2.2.1 Data Propagation and Replication
All the subscribers (peers) will receive the transactions in the same order in cryptographically linked blocks. A peer can be subscribed to more than one chain, but the chains do not interact with each other and each block received will contain only transactions corresponding to the corresponding business. Quorum [49] is another approach that aims to improve security by keeping the exclusive transactions shared only between the involved parties. The system is a hybrid between the global and selective disclosure paradigms, by allowing public transactions to be fully replicated and exclusive transactions to be shared only across the parties. The Quorum's privacy engine defines a private state tree that is updated with contracts and transactions that are sent point-to-point only to the interested parties. The private transaction contents are encrypted using Public Key cryptography, and only the users holding the private keys have access and can decrypt the actual content of the transaction. Proof of these events is also registered in the public chain, by hashing the encrypted private transaction. A similar permissioned implementation is also designed in Corda [61] where the network is formed of permission services, notary services, and peers. The system aims to provide redundancy while also keeping the transactions only known to the involving parts. Any transaction that occurs in the system must be signed and approved by both participants, and by the notary service responsible to validate transactions and prevent double-spending events. The notary service can be one entity or multiple entities that are coordinated by a consensus algorithm. In Table 4, the comparison between the Data propagation patterns found in the literature is presented. One of the biggest disadvantages of the current selective disclosure systems is their trust in different central authorities. The Quorum system requires some level of trust between the private parties, and the other systems rely on central authorities that are responsible either for forwarding the messages like in the case of the Hyperledger MultiChannel system or on authorities responsible to validate the integrity of transactions like in the case of Corda [61] or Plasma [62]. Consequently, selective disclosure should be considered only in trusted environments, where the central authorities can be considered a source of truth, while for public environments, global disclosure should be considered such that any party involved in the network can validate the integrity of the transactions. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multirow{2}{*}{**Platform**} & \multirow{2}{*}{**Trusted Paries**} & \multicolumn{2}{c}{**Global Disclosed**} & \multicolumn{2}{c}{**Selective Disclosed**} \\ \cline{3-6}  & & & **Data** & **Structure** & **Data** & **Structure** \\ \hline Public DLIs & Ethereum [15], Bitcoin [4], etc. & - & All transactions & Blockchain & - & - \\  & HyperLedger Multi-channel [60] & Orderer & - & - & Exclusive transactions & Queues, Blockchain \\ Business Specific & \multirow{2}{*}{Plasma [62]} & Central Authority, & Public Transactions & Blockchain & Exclusive transactions & Blockchain \\  & & N delegates & + settlements & & transactions & Blockchain \\  & & Corda [61] & Notary Service & - & - & Exclusive transactions & Local database \\  & & & Public transactions, & & Exclusive transactions & Merkle Patricia Tree \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  &