Journal: PLOS ONE

Article Title: The use of blockchain technology in enterprise financial accounting information sharing

doi: 10.1371/journal.pone.0298210

Figure Lengend Snippet: Structure of writing and deploying the blockchain smart contract model.

Article Snippet: The dataset is available at the Ethereum Blockchain (kaggle.com).

Techniques:

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: To reduce storage, if a block B is “voted” to be correct because the chain is long enough (ie, there are already many blocks created after B ), we can discard the transactions contained in B , without changing the hash of B ’s header (otherwise all blocks after B would need to be changed). To do this, instead of saving the content of all transactions directly in a block, we first compute the hash values of each transaction, and then construct a tree structure (a Merkle tree), to “combine” (ie, hash again) all hash values, and store only the Merkle Root hash value at the block header. This way we can prune the transactions in the tree later, without changing the Merkle Root and the block header. In other words, the size of the blockchain is now proportional to the number of blocks instead of being proportional to the number of transactions. (A) An example blockchain without a Merkle tree. The blocks enclose transactions without adopting a Merkle tree. As a result, the size of a block will grow proportionally to the number of transactions (eg, transaction T 12 ) that are enclosed. (B) A blockchain with a Merkle tree. A Merkle tree is constructed by hashing paired data (the leaves) to create a parent node iteratively, until a single hash, the Merkle Root, remains. In this example, the transactions (eg, T 12 ) are first encoded into a binary raw-transaction format and then hashed to create the hashes (eg, Hash of T 12 ). Then, hashes such as the Hash of T 12 are paired with other hashes such as the Hash of T 11 (if a hash does not have a pair, it simply duplicates itself to be paired) to compute the hash as their parent node (ie, Hash of T 11–12 ). The pairing/hashing process repeats until only 1 hash (the Merkle Root) remains, and the Merkle tree construction process is then completed. Finally, by only enclosing the Merkle Root in each block header, the storage space required to verify the integrity/validity of transactions can be reduced. That is, if an attacker tries to change the content of any transaction such as T 12 , all of the related hashes (ie, Hash of T 12 , Hash of T 11–12 , and Hash of T 11–14 ), and eventually the Merkle Root (ie, Hash of T 11–18 ) will also change and can be easily verified. To enclose this new Merkle Root to pass the verification process, the attacker then needs to re-create block B and all blocks thereafter, which is computationally expensive and is enough to prevent such modification. , A Merkle tree is the basis of lightweight nodes described in Figure 3 ( ie, the blockchain nodes that only need to verify transactions can store parts of the Merkle trees to save space, while the full blockchain nodes that need to “mine” new blocks store all of the Merkle trees).

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques: Blocking Assay, Construct, Modification

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: Another technique to reduce the need for each user to keep the full history of transactions is to use lightweight nodes together with a Merkle tree. For a user who only wants to use coins but does not want to “mine” new blocks, the full transaction history (more than 150 GB as of January 2018) is too large, especially for smartphones. Therefore, a user can adopt lightweight nodes so that only the Merkle Branch that links the transactions that the user would like to verify is used. An example of the Merkle Branch for transaction T 12 stored on a blockchain lightweight node (eg, on a mobile device), in contrast to the data storage of a full node (eg, on a personal computer), is shown in this figure. With the use of the Merkle tree, a lightweight node only stores data relevant to specific transactions (eg, T 12 ) to save space. For example, in addition to T 12 itself, this lightweight node only needs to store related hashes (ie, Hash of T 11 , Hash of T 13–14 , and Hash of T 15–18 ), instead of storing the full Merkle tree, to make sure T 12 is linked to block B . That is, one can first compute the Hash of T 12 using T 12 , and then compute the Hash of T 11–12 using the Hash of T 11 and the Hash of T 12 . Eventually, one can compute the value of the Merkle Root ( Hash of T 11–18 ), and compare it with the one stored in B , to make sure T 12 has been verified in B . This way, a lot of required storage space for those lightweight nodes is saved, making applications such as wallet apps on mobile devices feasible. This verifying process is also known as Simplified Payment Verification. , As a result, users/nodes can be divided into 2 groups: full nodes (the ones storing the whole transaction history and performing mining) and lightweight nodes (ie, the nodes using Simplified Payment Verification just for transactions, without mining), thus reducing the storage space for lightweight nodes and improving the scalability of a blockchain network.

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques: Blocking Assay

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: The ability of coin splitting and combining can further reduce the number of transactions and thus lower the burden of a blockchain network. To do this, intuitively one can just allow multiple inputs and multiple outputs. A special type of output is unspent transaction output ( UTXO ), ie, the “change” that is returned to the sender of the transaction and can be spent (ie, serve as an input) in the future transactions. In this example, Alice has 10 coins, which constitute the output of previous transactions. Alice sends 7 coins to Bob and receives 3 coins ( UTXO ) as change. After this transaction, the 3 coins ( UTXO ) are recorded in each full node. If Alice then tries to spend the original 10 coins instead of the 3 coins, each full node can detect such behavior by checking the UTXO list and reject the transaction accordingly. This way, UTXO helps identify double-spending. That is, each full node maintains a list of UTXO , and compares the input of new transactions against this list. If an input is not in the list, the transaction is considered double-spending and will be invalidated.

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques:

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: The Byzantine Generals' Problem refers to a distributed set of generals who need to reach a consensus/agreement on the timing of a simultaneous attack by multiple divisions of an army. ( A ) A simplified example of the relaxed version of the Byzantine Generals’ Problem, showing the difficulty generals have in agreeing on the proper time for an attack. There are several divisions of a Byzantine army camping outside an enemy city, and each division has its own commanding general who would like to, with other generals, reach consensus on the time to attack the city. That is, each general could make a decision about when to attack the city, but to be successful the majority of generals have to come up with an agreement about the attack time. However, the generals can only communicate with each other via messengers, and such communication form is nonsynchronized (eg, if 2 generals announce 2 different preferred times within a very close time frame, some generals may receive one time and other generals may receive another time). In this scenario, it is very difficult for the majority of generals to find a consensus time and execute a successful attack. ( B ) A Proof-of-Work (PoW) solution to the relaxed version of the Byzantine Generals’ Problem. To deal with Byzantine Generals’ Problem, many blockchain platforms have created consensus protocols to resolve disagreements within the chain. For example, PoW, the consensus protocol of the Bitcoin Blockchain, can find a solution to the relaxed version of the Byzantine Generals’ Problem, as described by the author Satoshi Nakamoto and proved by Miller and LaViola. The idea is for each general to first decide an attacking time (eg, at T 0 in this example) and start to do PoW (eg, at T 1 to find a solution to a difficult-to-compute yet easy-to-verify problem , ). Once the PoW is completed (eg, general G 3 finds the solution at T ), the winning general ( G 3 ) asks the messengers ( M 3 ) to broadcast the block containing G 3 ’s proposed attack time T (1 pm in this example) to the blockchain. Since the verification of PoW is relatively simple (ie, fast), other generals can verify the PoW easily. They pause their work because they would only be allowed to add their time after the one proposed by G 3. After confirming the PoW is valid, every other general agrees with G 3 that the attack will be at 1 pm . ( C ) The process to reach consensus among generals. After the first block ( B 1 ) with the time 1 pm is added to the blockchain, all generals restart PoW based on the hash of B 1 to find the second block ( B ). One important protocol is that all generals will do PoW based on the longest chain, which ensures the consensus. That is, suppose general G 4 also completed the PoW to propose another attack time (7 pm ) in block B 1 ’ : since another general ( G 5 ) has already created a block B to support 1 pm , the next general ( G 6 ) will only work on the longest chain to support 1 pm instead of 7 pm , thus the consensus attack time would eventually be 1 pm . Finally, after the blockchain is long enough, every general will be confident that the consensus attack time (1 pm ) has been agreed by the majority of generals. This is because many generals have been working on the longest chain, thus the probability of a successful consensus of attack time is now high enough to solve the distributed agreement problem.

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques: Blocking Assay

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: Data items extracted from the blockchain platforms

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques: Software, Transferring

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: Platforms included in this study, as of July 2017

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques:

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: Important items to consider when selecting a blockchain platform

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques: Software

Journal: Journal of the American Medical Informatics Association : JAMIA

Article Title: Comparison of blockchain platforms: a systematic review and healthcare examples

doi: 10.1093/jamia/ocy185

Figure Lengend Snippet: Blockchain technology

Article Snippet: Nebula Genomics proposes to share and analyze genomic data on an Ethereum-based blockchain platform.

Techniques: