412
X. Liu et al.
To give more details, here is how PBFT works in Fabric:
1. One of the nodes is elected as a leader.
2. Transaction requests are submitted to the leader.
3. The leader organizes the transactions into an ordered list and broadcasts this list
to all other nodes in the blockchain for validation.
4. Every validating node executes the ordered transactions one by one. Then it
calculates the hash code for the new block which is based on the received
transactions. Then this validating node broadcasts the hash code to other
validating nodes and starts counting the responses from them.
5. If a validating node realizes that two-thirds of all validation peers have the same
hash code, it will add the new block to its own copy of the ledger.
The PBFT model works only if the number of malicious nodes in a blockchain
does not exceed one-third of the total nodes in the system in a given time window.
The more nodes are there in the blockchain, the more unlikely for the malicious
nodes to reach one-third of the total nodes.
The PBFT algorithm has two main advantages compared to other consensus
algorithms. The first advantage is that it can finalize transactions and blocks without
needing confirmations as what is done in PoW. The second advantage of the PBFT
model is that it uses significantly reduced energy, again as compared to PoW.
There are two limitations to the PBFT consensus algorithm. First, it works well
only for blockchains of small sizes due to its communication model among nodes.
Second, it is susceptible to Sybil attacks. Due to the first limitation, the size of the
blockchain cannot be increased significantly just to mitigate Sybil attacks. Luckily,
possible solutions have been identified to solve this problem. For example, PBFT
can be interlaced with PoW to overcome both limitations.
8.3.4.5 IOTA
A totally different technology in the cryptocurrency family is IOTA [14]. IOTA is an
open-source distributed ledger with great potential for applications in the Internet of
Things.
IOTA works on the platform called Tangle. Tangle hashes use Winternitz
signatures [15] which is a hash-based cryptography, unlike blockchains that use
elliptic curve cryptography or ECC. Winternitz signatures are much faster than
ECC. The actual hash function used by Tangle is Kerl [16] which is a version of
SHA-3. Kerl works based on ternary operations, which is more secure than other
crypto technologies used in blockchains. Currently, many crypto algorithms can be
broken by superfast quantum computers. However, it is very difficult for a quantum
computer to break ternary operations used by Kerl. The chances of Tangle suffering
from a quantum attack are roughly 1 million times less than the blockchain.
X. Liu et al.
To give more details, here is how PBFT works in Fabric:
1. One of the nodes is elected as a leader.
2. Transaction requests are submitted to the leader.
3. The leader organizes the transactions into an ordered list and broadcasts this list
to all other nodes in the blockchain for validation.
4. Every validating node executes the ordered transactions one by one. Then it
calculates the hash code for the new block which is based on the received
transactions. Then this validating node broadcasts the hash code to other
validating nodes and starts counting the responses from them.
5. If a validating node realizes that two-thirds of all validation peers have the same
hash code, it will add the new block to its own copy of the ledger.
The PBFT model works only if the number of malicious nodes in a blockchain
does not exceed one-third of the total nodes in the system in a given time window.
The more nodes are there in the blockchain, the more unlikely for the malicious
nodes to reach one-third of the total nodes.
The PBFT algorithm has two main advantages compared to other consensus
algorithms. The first advantage is that it can finalize transactions and blocks without
needing confirmations as what is done in PoW. The second advantage of the PBFT
model is that it uses significantly reduced energy, again as compared to PoW.
There are two limitations to the PBFT consensus algorithm. First, it works well
only for blockchains of small sizes due to its communication model among nodes.
Second, it is susceptible to Sybil attacks. Due to the first limitation, the size of the
blockchain cannot be increased significantly just to mitigate Sybil attacks. Luckily,
possible solutions have been identified to solve this problem. For example, PBFT
can be interlaced with PoW to overcome both limitations.
8.3.4.5 IOTA
A totally different technology in the cryptocurrency family is IOTA [14]. IOTA is an
open-source distributed ledger with great potential for applications in the Internet of
Things.
IOTA works on the platform called Tangle. Tangle hashes use Winternitz
signatures [15] which is a hash-based cryptography, unlike blockchains that use
elliptic curve cryptography or ECC. Winternitz signatures are much faster than
ECC. The actual hash function used by Tangle is Kerl [16] which is a version of
SHA-3. Kerl works based on ternary operations, which is more secure than other
crypto technologies used in blockchains. Currently, many crypto algorithms can be
broken by superfast quantum computers. However, it is very difficult for a quantum
computer to break ternary operations used by Kerl. The chances of Tangle suffering
from a quantum attack are roughly 1 million times less than the blockchain.