## 2 Background
### Iota  
The IOTA is a distributed ledger technology to manage secure data transmission between different IoT devices. The main difference between the IOTA and other distributed ledger technologies is that it utilizes the directed acrylic graph (DAG) structure called the \"Tangle\" in place of the conventional blockchain. IOTA is highly scalable [19] since there are no blocks in its DAG structure, which leads to a faster confirmation of transactions, unlike in the case of blockchain. Making a transaction on IOTA consumes less energy [20] as compared to other distributed ledgers and, hence, the adoption of IOTA in low power devices such as the IoT becomes rudimentary.  
The scalable architecture of the IOTA Tangle enables faster transaction confirmation, as shown in Figure 2. In Figure 2, each square represents a transaction and the arrows also known as edges connect these transactions to form a Tangle. There are three types of transactions, called tips, ongoing transactions, and approved transactions, as shown in Figure 2. Tips are the unconfirmed transactions that are new and have just been added to the ledger. Ongoing transactions are the transactions that have been added to the ledger and are waiting to be referenced by new transactions [21] to achieve confirmation. Approved transactions are the transactions that have been confirmed or have been referenced by all the tips, either directly or indirectly.  
The working model and the security of the IOTA protocols were designed with quantum computers in mind, as well as environments with constraints on bandwidth. The Winternitz one-time signature system, which protects against quantum computer access, is used in the IOTA protocol. This one-time signature approach enables effective broadcast authentication in sensor networks since the communication and computing needs are low. As there is no transaction fee for publishing a transaction to IOTA, it can be seamlessly used to send transactions, store data, and ensure data integrity with time. A data transmission protocol [22] called masked authenticated messaging (MAM) enables a user to publish streams of encrypted data in the form of transactions. Participants can broadcast a message at any time by forming a channel [23]. Subscribers can subscribe to the channel of the publisher to receive the data by using the address of the transactions. However, a small amount of proof-of-work is necessary for the data to circulate through the network and prevent spamming. MAM allows the user to send encrypted data streams that are a chain of messages or sensor data to IOTA with zero cost per transaction through the Tangle.  
Forward secrecy and quantum-resistant cryptography are the two most important features of MAM implementation. Attacks by a quantum machine [24] that is adequately powerful can be resisted due to the secure post-quantum cryptographic algorithms. Many cryptographic algorithms traversing today over the Internet that are presently used to encrypt data [25] are not sufficiently secure. MAM is a useful protocol to transmit confidential data, due to the feature of forward secrecy. Every transaction is linked to the next transaction with a pointer known as next root, which is a Merkle root of the next transaction. As a result, the transaction at the point of entry and the subsequent transactions linked to it can be retrieved efficiently. However, it becomes infeasible for a user to fetch transactions before their point of entry due to forward transaction linking, as shown in Figure 3.