Patent Publication Number: US-11381573-B2

Title: Parallel execution of transactions in a blockchain network based on smart contract whitelists

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the benefit of priority of U.S. patent application Ser. No. 16/422,192, filed May 24, 2019, which is a continuation of PCT Application No. PCT/CN2018/124873, filed on Dec. 28, 2018, both of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Distributed ledger systems (DLSs), which can also be referred to as consensus networks, and/or blockchain networks, enable participating entities to securely, and immutably store data. DLSs are commonly referred to as blockchain networks without referencing any particular user case. Examples of types of blockchain networks can include public blockchain networks, private blockchain networks, and consortium blockchain networks. A consortium blockchain network is provided for a select group of entities, which control the consensus process, and includes an access control layer. 
     A smart contract is a set of executable software instructions stored and executed by a blockchain network. Smart contracts are generally stored unencrypted and therefore are visible to all participants in the blockchain network. Participants in the blockchain network can write and publish their own smart contracts, and generally can also call smart contracts that have already been deployed in the blockchain network. 
     One issue encountered in blockchain networks is the speed at which transactions (including smart contract calls) are processed. Generally, nodes in the blockchain network process transactions serially in the order they are submitted. This can lead to low transaction throughput and delays between when a transaction is submitted and when it clears. 
     Techniques to address these transaction performance issues in a blockchain network would be advantageous. 
     SUMMARY 
     Implementations of this specification include computer-implemented methods for parallel execution of transactions in a blockchain network based on smart contract whitelists. More particularly, implementations of this specification are directed to techniques for to executing groups of transactions and smart contract calls having a shared dependency in parallel with other groups. 
     In some implementations, actions include identifying a plurality of transactions to be executed in the blockchain, wherein the transactions are arranged in an execution order, wherein the transactions include one or more smart contract calls to smart contracts each having a whitelist identifying one or more accounts that are authorized to execute the smart contract, and wherein the execution order includes a smart contract call to a smart contract that does not have a whitelist arranged after the plurality of transactions; identifying groups of transactions within the plurality of transactions, wherein the transactions in each group are associated with a particular set of accounts in the blockchain network, and wherein the particular set of accounts associated with each of the one or more smart contract calls is determined based on the whitelist associated with the smart contract call; instructing nodes of the blockchain network to execute each of the groups of transactions in parallel, wherein executing each group of transactions includes executing the transactions within the group serially and according to the execution order; determining that the nodes of the blockchain network have completed executing all of the groups of transactions; and in response determining that the nodes of the blockchain network have completed executing all of the groups of transactions, instructing the nodes of the blockchain network to execute the smart contract call that does not include a whitelist. Other implementations include corresponding systems, apparatus, and computer programs, configured to perform the actions of the methods, encoded on computer storage devices. 
     These and other implementations may each optionally include one or more of the following features: 
     In some cases, instructing nodes of the blockchain network to execute each of the groups of transactions in parallel includes instructing a first set of nodes to execute a first group of transactions and instructing a first set of nodes to execute a second group of transactions. 
     In some implementations, determining that the nodes of the blockchain network have completed executing all of the groups of transactions includes determining that all transactions in the plurality of transactions have been included in one or more blocks stored in a blockchain maintained by the blockchain network. 
     In some cases, instructing nodes of the blockchain network to execute each of the groups of transactions in parallel includes sending a message to the nodes over a network. 
     In some cases, identifying the plurality of transactions to be executed in the blockchain includes receiving transactions broadcast to the blockchain network. 
     In some implementations, the whitelist is included within a set of executable instructions associated with each smart contract. 
     In some cases, the whitelist is separate from a set of executable instructions associated with each smart contract. 
     In some implementations, the whitelist includes an identification of the one or more accounts that are authorized to access each smart contract. 
     In some cases, the whitelist includes a reference to a location external to each smart contract that stores the one or more that are authorized to access each smart contract. 
     This specification also provides one or more non-transitory computer-readable storage media coupled to one or more processors and having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations in accordance with implementations of the methods provided herein. 
     This specification further provides a system for implementing the methods provided herein. The system includes one or more processors, and a computer-readable storage medium coupled to the one or more processors having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations in accordance with implementations of the methods provided herein. 
     It is appreciated that methods in accordance with this specification may include any combination of the aspects and features described herein. That is, methods in accordance with this specification are not limited to the combinations of aspects and features specifically described herein, but also include any combination of the aspects and features provided. 
     The details of one or more implementations of this specification are set forth in the accompanying drawings and the description below. Other features and advantages of this specification will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts an example of an environment that can be used to execute implementations of this specification. 
         FIG. 2  depicts an example of a conceptual architecture in accordance with implementations of this specification. 
         FIG. 3  depicts an example of an environment for enabling smart contract whitelists in accordance with implementations of this specification. 
         FIG. 4A  depicts an example of an execution order for transactions in a blockchain network in accordance with implementations of this specification. 
         FIG. 4B  depicts an example of a parallel execution order for transactions in a blockchain network in accordance with implementations of this specification. 
         FIG. 5  depicts an example of a process that can be executed in accordance with implementations of this specification. 
         FIG. 6  depicts examples of modules of an apparatus in accordance with implementations of this specification. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Implementations of this specification include computer-implemented methods for enforcing account whitelists for smart contracts. More particularly, implementations of this specification are directed to techniques for allowing the creator of a smart contract to define a whitelist specifying which accounts can call the smart contract. 
     To provide further context for implementations of this specification, and as introduced above, distributed ledger systems (DLSs), which can also be referred to as consensus networks (e.g., made up of peer-to-peer nodes), and blockchain networks, enable participating entities to securely, and immutably conduct transactions, and store data. The term blockchain is used herein to generally refer to a DLS without reference to any particular use case. 
     A blockchain is a data structure that stores transactions in a way that the transactions are immutable, and can be subsequently verified. A blockchain includes one or more blocks. Each block in the chain is linked to a previous block immediately before it in the chain by including a cryptographic hash of the previous block. Each block also includes a timestamp, its own cryptographic hash, and one or more transactions. The transactions, which have already been verified by the nodes of the blockchain network, are hashed and encoded into a Merkle tree. A Merkle tree is a data structure in which data at the leaf nodes of the tree is hashed, and all hashes in each branch of the tree are concatenated at the root of the branch. This process continues up the tree to the root of the entire tree, which stores a hash that is representative of all data in the tree. A hash purporting to be of a transaction stored in the tree can be quickly verified by determining whether it is consistent with the structure of the tree. 
     Whereas a blockchain is a data structure for storing transactions, a blockchain network is a network of computing nodes that manage, update, and maintain one or more blockchains. As introduced above, a blockchain network can be provided as a public blockchain network, a private blockchain network, or a consortium blockchain network. 
     In a public blockchain network, the consensus process is controlled by nodes of the consensus network. For example, hundreds, thousands, even millions of entities can cooperate a public blockchain network, each of which operates at least one node in the public blockchain network. Accordingly, the public blockchain network can be considered a public network with respect to the participating entities. In some examples, a majority of entities (nodes) must sign every block in order for the block to be valid, and added to the blockchain (distributed ledger) of the blockchain network. Example public blockchain networks include particular peer-to-peer payment networks that leverage a distributed ledger, referred to as blockchain. As noted above, the term blockchain, however, is used to generally refer to distributed ledgers without particular reference to any particular blockchain network. 
     In general, a consortium blockchain network is private among the participating entities. In a consortium blockchain network, the consensus process is controlled by an authorized set of nodes, one or more nodes being operated by a respective entity (e.g., a financial institution, insurance company). For example, a consortium of ten (10) entities (e.g., financial institutions, insurance companies) can operate a consortium blockchain network, each of which operates at least one node in the consortium blockchain network. Accordingly, the consortium blockchain network can be considered a private network with respect to the participating entities. In some examples, each entity (node) must sign every block in order for the block to be valid, and added to the blockchain. In some examples, at least a sub-set of entities (nodes) (e.g., at least 7 entities) must sign every block in order for the block to be valid, and added to the blockchain. 
     It is contemplated that implementations of this specification can be realized in any appropriate type of blockchain network. 
     Implementations of this specification are described in further detail herein in view of the above context. More particularly, and as introduced above, implementations of this specification are directed to techniques for allowing the creator of a smart contract to define a whitelist specifying which accounts can call the smart contract. 
     Generally, a smart contract is a set of one or more computer instructions that are stored in a blockchain and executed by nodes of a blockchain network. The code for a smart contract is generally transformed into a form that is executable by the nodes of the blockchain network (e.g., bytecode) and either the bytecode itself or bytecode configured to retrieve the smart contract bytecode is stored in the blockchain. Functions defined in the smart contract code can then be called by participants in the blockchain network, causing nodes to execute the instructions in the called function. 
     This specification describes techniques that allow the creator of a smart contract to specify a list of accounts (a whitelist) in the blockchain network that are permitted to call the smart contract. When a participant in the blockchain network calls a smart contract deployed in the blockchain managed by the blockchain network, the participant provides an account as part of the call. The blockchain network checks the whitelist associated with the smart contract for the participant&#39;s account. If the participant&#39;s account is in the whitelist, the blockchain network executes the smart contract call. If the participant&#39;s account is not in the whitelist, the blockchain network does not execute the smart contract call. The blockchain network may also store a record of the participant&#39;s failed attempt to access the smart contract. 
     Implementations of this specification are directed to executing groups of transactions (including smart contact calls) having a shared dependency (i.e., affecting the same accounts) in parallel with other groups. The accounts affected by a smart contract call can be determined based on the whitelist associated with the smart contract. Because transactions in different groups have no dependency on one another (e.g., do not affect the same accounts in the blockchain network) the order in which transactions in different groups are executed relative to one another does not affect the overall state of the blockchain network. Thus, these transactions can be executed in parallel, which can lead to an increase in transaction throughput in a blockchain network. 
       FIG. 1  depicts an example of an environment  100  that can be used to execute implementations of this specification. In some examples, the environment  100  enables entities to participate in a blockchain network  102 . The environment  100  includes computing devices  106 ,  108 , and a network  110 . In some examples, the network  110  includes a local area network (LAN), wide area network (WAN), the Internet, or a combination thereof, and connects web sites, user devices (e.g., computing devices), and back-end systems. In some examples, the network  110  can be accessed over a wired and/or a wireless communications link. In some examples, the network  110  enables communication with, and within the blockchain network  102 . In general the network  110  represents one or more communication networks. In some cases, the computing devices  106 ,  108  can be nodes of a cloud computing system (not shown), or can each computing device  106 ,  108  be a separate cloud computing system including a plurality of computers interconnected by a network and functioning as a distributed processing system. 
     In the depicted example, the computing systems  106 ,  108  can each include any appropriate computing system that enables participation as a node in the blockchain network  102 . Examples of computing devices include, without limitation, a server, a desktop computer, a laptop computer, a tablet computing device, and a smartphone. In some examples, the computing systems  106 ,  108  host one or more computer-implemented services for interacting with the blockchain network  102 . For example, the computing system  106  can host computer-implemented services of a first entity (e.g., Participant A), such as transaction management system that the first entity uses to manage its transactions with one or more other entities (e.g., other participants). The computing system  108  can host computer-implemented services of a second entity (e.g., Participant B), such as transaction management system that the second entity uses to manage its transactions with one or more other entities (e.g., other participants). In the example of  FIG. 1 , the blockchain network  102  is represented as a peer-to-peer network of nodes, and the computing systems  106 ,  108  provide nodes of the first entity, and second entity respectively, which participate in the blockchain network  102 . 
       FIG. 2  depicts an example of a conceptual architecture  200  in accordance with implementations of this specification. The example of a conceptual architecture  200  includes participant systems  202 ,  204 ,  206  that correspond to Participant A, Participant B, and Participant C, respectively. Each participant (e.g., user, enterprise) participates in a blockchain network  212  provided as a peer-to-peer network including a plurality of nodes  214 , at least some of which immutably record information in a blockchain  216 . Although a single blockchain  216  is schematically depicted within the blockchain network  212 , multiple copies of the blockchain  216  are provided, and are maintained across the blockchain network  212 , as described in further detail herein. 
     In the depicted example, each participant system  202 ,  204 ,  206  is provided by, or on behalf of Participant A, Participant B, and Participant C, respectively, and functions as a respective node  214  within the blockchain network. As used herein, a node generally refers to an individual system (e.g., computer, server) that is connected to the blockchain network  212 , and enables a respective participant to participate in the blockchain network. In the example of  FIG. 2 , a participant corresponds to each node  214 . It is contemplated, however, that a participant can operate multiple nodes  214  within the blockchain network  212 , and/or multiple participants can share a node  214 . In some examples, the participant systems  202 ,  204 ,  206  communicate with, or through the blockchain network  212  using a protocol (e.g., hypertext transfer protocol secure (HTTPS)), and/or using remote procedure calls (RPCs). 
     Nodes  214  can have varying degrees of participation within the blockchain network  212 . For example, some nodes  214  can participate in the consensus process (e.g., as minder nodes that add blocks to the blockchain  216 ), while other nodes  214  do not participate in the consensus process. As another example, some nodes  214  store a complete copy of the blockchain  216 , while other nodes  214  only store copies of portions of the blockchain  216 . For example, data access privileges can limit the blockchain data that a respective participant stores within its respective system. In the example of  FIG. 2 , the participant systems  202 ,  204 ,  206  store respective, complete copies  216 ′,  216 ″,  216 ′″ of the blockchain  216 . 
     A blockchain (e.g., the blockchain  216  of  FIG. 2 ) is made up of a chain of blocks, each block storing data. Examples of data include transaction data representative of a transaction between two or more participants. While transactions are used herein by way of non-limiting example, it is contemplated that any appropriate data can be stored in a blockchain (e.g., documents, images, videos, audio). Examples of transactions can include, without limitation, exchanges of something of value (e.g., assets, products, services). The transaction data is immutably stored within the blockchain. That is, the transaction data cannot be changed. 
     Before storing in a block, the transaction data is hashed. Hashing is a process of transforming the transaction data (provided as string data) into a fixed-length hash value (also provided as string data). It is not possible to un-hash the hash value to obtain the transaction data. Hashing ensures that even a slight change in the transaction data results in a completely different hash value. Further, and as noted above, the hash value is of fixed length. That is, no matter the size of the transaction data the length of the hash value is fixed. Hashing includes processing the transaction data through a hash function to generate the hash value. An examples of hash function includes, without limitation, the secure hash algorithm (SHA)-256, which outputs 256-bit hash values. 
     Transaction data of multiple transactions are hashed and stored in a block. For example, hash values of two transactions are provided, and are themselves hashed to provide another hash. This process is repeated until, for all transactions to be stored in a block, a single hash value is provided. This hash value is referred to as a Merkle root hash, and is stored in a header of the block. A change in any of the transactions will result in change in its hash value, and ultimately, a change in the Merkle root hash. 
     Blocks are added to the blockchain through a consensus protocol. Multiple nodes within the blockchain network participate in the consensus protocol, and compete to have a block added to the blockchain. Such nodes are referred to as miners (or miner nodes). POW, introduced above, is used as a non-limiting example. 
     The miner nodes execute the consensus process to add transactions to the blockchain. Although multiple miner nodes participate in the consensus process, only one miner node can write the block to the blockchain. That is, the miner nodes compete in the consensus process to have their block added to the blockchain. In further detail, a miner node periodically collects pending transactions from a transaction pool (e.g., up to a predefined limit on the number of transactions that can be included in a block, if any). The transaction pool includes transaction messages from participants in the blockchain network. The miner node constructs a block, and adds the transactions to the block. Before adding the transactions to the block, the miner node checks whether any of the transactions are already included in a block of the blockchain. If a transaction is already included in another block, the transaction is discarded. 
     The miner node generates a block header, hashes all of the transactions in the block, and combines the hash value in pairs to generate further hash values until a single hash value is provided for all transactions in the block (the Merkle root hash). This hash is added to the block header. The miner also determines the hash value of the most recent block in the blockchain (i.e., the last block added to the blockchain). The miner node also adds a nonce value, and a timestamp to the block header. In a mining process, the miner node attempts to find a hash value that meets required parameters. The miner node keeps changing the nonce value until finding a hash value that meets the required parameters. 
     Every miner in the blockchain network attempts to find a hash value that meets the required parameters, and, in this way, compete with one another. Eventually, one of the miner nodes finds a hash value that meets the required parameters, and advertises this to all other miner nodes in the blockchain network. The other miner nodes verify the hash value, and if determined to be correct, verifies each transaction in the block, accepts the block, and appends the block to their copy of the blockchain. In this manner, a global state of the blockchain is consistent across all miner nodes within the blockchain network. The above-described process is the POW consensus protocol. 
     A non-limiting example is provided with reference to  FIG. 2 . In this example, Participant A wants to send an amount to Participant B. Participant A generates a transaction message (e.g., including From, To, and Value fields), and sends the transaction message to the blockchain network, which adds the transaction message to a transaction pool. Each miner node in the blockchain network creates a block, and takes all transactions from the transaction pool (e.g., up to a predefined limit on the number of transaction that can be added to a block, if any), and adds the transactions to the block. In this manner the transaction published by Participant A is added to the blocks of the miner nodes. 
     In some blockchain networks, cryptography is implemented to maintain privacy of transactions. For example, if two nodes want to keep a transaction private, such that other nodes in the blockchain network cannot discern details of the transaction, the nodes can encrypt the transaction data. Examples of cryptographic methods include, without limitation, symmetric encryption, and asymmetric encryption. Symmetric encryption refers to an encryption process that uses a single key for both encryption (generating ciphertext from plaintext), and decryption (generating plaintext from ciphertext). In symmetric encryption, the same key is available to multiple nodes, so each node can en-/de-crypt transaction data. 
     Asymmetric encryption uses keys pairs that each include a private key, and a public key, the private key being known only to a respective node, and the public key being known to any or all other nodes in the blockchain network. A node can use the public key of another node to encrypt data, and the encrypted data can be decrypted using other node&#39;s private key. For example, and referring again to  FIG. 2 , Participant A can use Participant B&#39;s public key to encrypt data, and send the encrypted data to Participant B. Participant B can use its private key to decrypt the encrypted data (ciphertext) and extract the original data (plaintext). Messages encrypted with a node&#39;s public key can only be decrypted using the node&#39;s private key. 
     Asymmetric encryption is used to provide digital signatures, which enables participants in a transaction to confirm other participants in the transaction, as well as the validity of the transaction. For example, a node can digitally sign a message, and another node can confirm that the message was sent by the node based on the digital signature of Participant A. Digital signatures can also be used to ensure that messages are not tampered with in transit. For example, and again referencing  FIG. 2 , Participant A is to send a message to Participant B. Participant A generates a hash of the message, and then, using its private key, encrypts the hash to provide a digital signature as the encrypted hash. Participant A appends the digital signature to the message, and sends the message with digital signature to Participant B. Participant B decrypts the digital signature using the public key of Participant A, and extracts the hash. Participant B hashes the message and compares the hashes. If the hashes are same, Participant B can confirm that the message was indeed from Participant A, and was not tampered with. 
       FIG. 3  depicts an example of an environment  300  for enabling smart contract whitelists in accordance with implementations of this specification. As shown, a smart contract  302  is stored in the blockchain  216  of the blockchain network  212  of  FIG. 2 . The smart contract  302  includes instructions  304  and a whitelist  306 . The whitelist  306  includes one or more account  308 . 
     As described above, the smart contract  302  is stored in the blockchain  216 . Participants in the blockchain network  212  can call the smart contract  302 , which can cause nodes  214  of the blockchain network  212  to execute the instructions  304 . In some implementations, the nodes  214  of the blockchain network will check whether an account specified by the caller of the smart contract is included in the one or more accounts  308  specified by the whitelist  306 . If the account is in the whitelist  306 , the nodes  214  execute the instructions  304 . If the account is not in the whitelist  306 , the nodes  214  do not execute the instructions  304 . 
     In some implementations, the instructions  304  can be software code written in a high level programming language supported by the nodes  214  of the blockchain network  212 , such as, for example, Solidity, Serpent, LLL, Viper, Mutan, C, C++, Python, Java, Javascript, or other programming languages. The instructions  304  may also be compiled bytecode generated from software code associated with the smart contract  302 . 
     In some implementations, the whitelist  306  and the accounts  308  are stored in the blockchain  216  along with the smart contract  302 . In some cases, the whitelist  306  and the accounts  308  are included within the instructions  304  of the smart contract  302 . For example, the whitelist  306  may be included in a directive in the instructions  304 , such as a pre-processor instruction or a specially formatted comment. The whitelist  306  may also be included using a construct specific to the programming language used to author the smart contract, such as a function decorator. The whitelist  306  may also be specified in executable instructions within the instructions  304 . In some implementations, the whitelist  306  is examined prior to the nodes  214  executing the instructions  304 . In some cases, such as when the whitelist  306  is included in the executable instructions, the nodes  214  may begin execution of the instructions  304  before evaluating the whitelist  306 . For example, the smart contract  302  could include a private function defined with the instructions  304  that would take the caller&#39;s account as a parameter and verify that the caller is authorized to call the smart contract based on the whitelist  306 . Such a function could be called automatically when the smart contract  302  is executed, and the smart contract  302  could simply exit if the account of the caller is not authorized to execute the contract. In some cases, the node  214  that is executing the smart contract  302  could call the private function to check the whitelist  306 , and only execute the main function of the smart contract  302  if the call to the private function indicates that the caller&#39;s account is authorized to execute the smart contract  302 . 
       FIG. 4A  depicts an example of an execution order  400  for transactions in a blockchain network in accordance with implementations of this specification. As shown, the execution order  400  includes a plurality of transactions ( 405 ,  410 ,  415 ,  420 ) sequenced according to the order in which they are to be executed by nodes of a blockchain network. Transaction  405   a ,  405   b , and  405   c  are calls to smart contracts. In addition the smart contract calls, the execution order  400  includes multiple groups of transactions sharing a common dependency (denoted by cross hatching), such as, for example, affecting the same account or accounts. Smart contract calls  405   a  and  405   b  are grouped together with other transactions based on the contents of their respective whitelists, which define the accounts that can execute the smart contract and thus can have their state changed by the smart contract. As described below, each group of transactions can be executed in parallel by the nodes of the blockchain network according to implementations of this specification. 
       FIG. 4B  depicts an example of a parallel execution order  450  for transactions in a blockchain network in accordance with implementations of this specification. As shown, in the parallel execution order  450 , groups of transactions  455 ,  460 , and  465  have been identified. Nodes of a blockchain network can execute the groups of transactions in parallel, as shown in the  FIG. 4B  and discussed above. In some cases, all transactions in a group share a common dependency, and therefore are executed serially according to the original execution order. This ensures that the state of the blockchain network (e.g., the account balances) will be the same as a result of executing the transactions according to the parallel execution order  450  as it would be after executing the transactions according to the execution order  400  in  FIG. 4A . 
     Consider the example where account A has a balance of $0 before executing any of the transactions in  FIG. 4B , where transaction  410   a  represents a payment to account A from account B in the amount of $400, and transaction  410   b  represents a payment from account A to account C of $50. If the transactions  410   a  and  410   b  are executed serially (as originally described in the execution order  400 ), account A will first be funded with $400, and then debited by $50, leaving a balance of $250. However, if the transactions  410   a  and  410   b  are not executed serially, and transaction  410   b  is executed before  410   a , the account A will have a balance of $0 when the payment of transaction  410   b  is executed. Account A will have an insufficient balance to fund the payment in this scenario, which could lead to transaction  410   b  being rejected by the blockchain network. 
     Building on this example, consider a case where transaction  420   a  represents a payment from an account D to an account E of $100. Because the accounts affected by transaction  420   a  (accounts D and E) do not include any of the accounts affected by transactions  410   a  and  410   b  (accounts A, B, and C), transaction  420   a  has no common dependency with transactions  410   a  and  410   b . Thus, transaction  420   a  can be executed in parallel with transactions  410   a  and  410   b.    
     Smart contract calls (e.g.,  405   a - c ) are different from other types of transactions in that the accounts that the execution of a smart contract will affect may not be determinable based on the smart contract itself. Since a smart contract is an executable software program that can be called by any participant in the blockchain network, it can theoretically affect any account in the blockchain network. However, with the addition of the whitelists described above, the accounts that a particular smart contract can affect can be determined. Because only accounts in the whitelist can cause the smart contract to execute, only those accounts have the potential to have their state (e.g., their balance) changed by execution of the smart contract. The whitelist thus allows smart contract calls to be grouped for parallel execution in the blockchain network along with other transactions affecting the same accounts. 
     In some implementations, transactions to be executed serially can be grouped together. For example, as shown in the  FIG. 4B , transactions  410   a - b  and smart contract call  405   b  are grouped in  455 , transactions  415   a - e  are grouped in  460 , and transactions  420   a - c  and smart contract call  405   a  are grouped in  465 . Each of the groups  455 ,  460  and  465  can be executed in parallel by the nodes of the blockchain network. Executing the transaction groups  455 ,  460 , and  465  in parallel can lead to an increase in transaction throughput on the blockchain network, as the network is now executing three transactions at any one time in parallel rather than just one if all transactions were executed serially. 
     In some implementations, if a smart contract includes no whitelist, any account in the blockchain network can execute the smart contract. Smart contract call  405   c  is a smart contract call that does not specify a whitelist. Because smart contract call  405   c  can be executed by any account in the blockchain network, it cannot be executed in parallel with other transactions. Contract call  405   c  represents a synchronization point, where parallel execution converges. Because contract calls lead to the execution of the instructions making up the smart contract, it may not be possible to determine the scope of accounts a particular contract call will affect. For example, consider a simple smart contract that takes a particular account and a payment amount as parameters, and applies the payment amount to the particular account if some condition is true. Because a caller of this smart contract specifies the particular account when the smart contract is called, it is not possible to determine, from the definition of the smart contract itself (i.e., its source code) which accounts a particular call to the smart contract will affect. For this reason, in some implementations, the contract call can be seen as a transaction with the potential to affect all accounts in the blockchain network, which therefore cannot be executed in parallel with other transactions. Thus, the parallel execution order  450  converges when it reaches contract call  405   c . For example, as shown, groups  455 ,  460 , and  465  execute in parallel until reaching contract call  405   c . At this point, the blockchain network waits until all transactions in the groups  455 ,  460 , and  465  have completed execution, and then proceeds with execution of the smart contract call  405   c.    
       FIG. 5  depicts an example of a process  500  that can be executed in accordance with implementations of this specification. In some implementations, the process  400  may be performed using one or more computer-executable programs executed using one or more computing devices. 
     At  502 , a plurality of transactions to be executed in the blockchain are identified. The transactions are arranged in an execution order, and may include one or more smart contract calls to smart contracts each having a whitelist identifying one or more accounts that are authorized to execute the smart contract. The execution order includes a smart contract call to a smart contract that does not have a whitelist arranged after the plurality of transactions. In some cases, identifying the plurality of transactions to be executed in the blockchain includes receiving transactions broadcast to the blockchain network. In some implementations, the whitelist for each smart contract is included within a set of executable instructions associated with each smart contract. The whitelist may be separate from a set of executable instructions associated with each smart contract. The whitelist can include an identification of the one or more accounts that are authorized to access each smart contract. In some cases, the whitelist includes a reference to a location external to each smart contract that stores the one or more that are authorized to access each smart contract. 
     At  504 , groups of transactions are identified within the plurality of transactions, wherein the transactions in each group are associated with a particular set of accounts in the blockchain network, and wherein the particular set of accounts associated with each of the one or more smart contract calls is determined based on the whitelist associated with the smart contract call. 
     At  506 , nodes of the blockchain network are instructed to execute each of the groups of transactions in parallel, wherein executing each group of transactions includes executing the transactions within the group serially and according to the execution order. In some cases, instructing nodes of the blockchain network to execute each of the groups of transactions in parallel includes instructing a first set of nodes to execute a first group of transactions and instructing a first set of nodes to execute a second group of transactions. In some cases, instructing nodes of the blockchain network to execute each of the groups of transactions in parallel includes sending a message to the nodes over a network. 
     At  508 , a determination is made that the nodes of the blockchain network have completed executing all of the groups of transactions. In some cases, determining that the nodes of the blockchain network have completed executing all of the groups of transactions includes determining that all transactions in the plurality of transactions have been included in one or more blocks stored in a blockchain maintained by the blockchain network. 
     At  510 , in response to determining that the nodes of the blockchain network have completed executing all of the groups of transactions, the nodes of the blockchain network are instructed to execute the smart contract call that does not include a whitelist. 
       FIG. 6  depicts examples of modules of an apparatus  600  in accordance with implementations of this specification. The apparatus  500  can be an example implementation of an apparatus configured to enable parallel execution of transactions in a blockchain network, such as a consortium blockchain network. The apparatus  600  can correspond to the implementations described above, and the apparatus  600  includes the following: an first identifier or first identifying unit  602  identifying a plurality of transactions to be executed in the blockchain, wherein the transactions are arranged in an execution order, wherein the transactions include one or more smart contract calls to smart contracts each having a whitelist identifying one or more accounts that are authorized to execute the smart contract, and wherein the execution order includes a smart contract call to a smart contract that does not have a whitelist arranged after the plurality of transactions; a second identifier or second identifying unit  604  for identifying groups of transactions within the plurality of transactions, wherein the transactions in each group are associated with a particular set of accounts in the blockchain network, and wherein the particular set of accounts associated with each of the one or more smart contract calls is determined based on the whitelist associated with the smart contract call; a first instructor or first instructing unit  606  for instructing nodes of the blockchain network to execute each of the groups of transactions in parallel, wherein executing each group of transactions includes executing the transactions within the group serially and according to the execution order; a determiner or determining unit  608  for determining that the nodes of the blockchain network have completed executing all of the groups of transactions; and a second instructor or second instructing unit  610  for instructing the nodes of the blockchain network to execute the smart contract call that does not include a whitelist in response determining that the nodes of the blockchain network have completed executing all of the groups of transactions. 
     The system, apparatus, module, or unit illustrated in the previous implementations can be implemented by using a computer chip or an entity, or can be implemented by using a product having a certain function. A typical implementation device is a computer, and the computer can be a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email receiving and sending device, a game console, a tablet computer, a wearable device, or any combination of these devices. 
     For an implementation process of functions and roles of each unit in the apparatus, references can be made to an implementation process of corresponding steps in the previous method. Details are omitted here for simplicity. 
     Because an apparatus implementation basically corresponds to a method implementation, for related parts, references can be made to related descriptions in the method implementation. The previously described apparatus implementation is merely an example. The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a number of network units. Some or all of the modules can be selected based on actual demands to achieve the objectives of the solutions of the specification. A person of ordinary skill in the art can understand and implement the implementations of the present application without creative efforts. 
     Referring again to  FIG. 6 , it can be interpreted as illustrating an internal functional module and a structure of an apparatus for enabling parallel execution of transactions in a blockchain network. The parallel execution apparatus can be an example of an apparatus configured to enable parallel execution of transactions in a blockchain network. 
     Implementations of the subject matter and the actions and operations described in this specification can be implemented in digital electronic circuitry, in tangibly-embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer programs, e.g., one or more modules of computer program instructions, encoded on a computer program carrier, for execution by, or to control the operation of, data processing apparatus. The carrier may be a tangible non-transitory computer storage medium. Alternatively, or in addition, the carrier may be an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. The computer storage medium can be or be part of a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of one or more of them. A computer storage medium is not a propagated signal. 
     The term “data processing apparatus” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. Data processing apparatus can include special-purpose logic circuitry, e.g., an FPGA (field programmable gate array), an ASIC (application-specific integrated circuit), or a GPU (graphics processing unit). The apparatus can also include, in addition to hardware, code that creates an execution environment for computer programs, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. 
     A computer program, which may also be referred to or described as a program, software, a software application, an app, a module, a software module, an engine, a script, or code, can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages; and it can be deployed in any form, including as a stand-alone program or as a module, component, engine, subroutine, or other unit suitable for executing in a computing environment, which environment may include one or more computers interconnected by a data communication network in one or more locations. 
     A computer program may, but need not, correspond to a file in a file system. A computer program can be stored in a portion of a file that holds other programs or data, e.g., one or more scripts stored in a markup language document, in a single file dedicated to the program in question, or in multiple coordinated files, e.g., files that store one or more modules, sub-programs, or portions of code. 
     The processes and logic flows described in this specification can be performed by one or more computers executing one or more computer programs to perform operations by operating on input data and generating output. The processes and logic flows can also be performed by special-purpose logic circuitry, e.g., an FPGA, an ASIC, or a GPU, or by a combination of special-purpose logic circuitry and one or more programmed computers. 
     Computers suitable for the execution of a computer program can be based on general or special-purpose microprocessors or both, or any other kind of central processing unit. Generally, a central processing unit will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer can include a central processing unit for executing instructions and one or more memory devices for storing instructions and data. The central processing unit and the memory can be supplemented by, or incorporated in, special-purpose logic circuitry. 
     Generally, a computer will be coupled to at least one non-transitory computer-readable storage medium (also referred to as a computer-readable memory). The storage medium coupled to the computer can be an internal component of the computer (e.g., an integrated hard drive) or an external component (e.g., universal serial bus (USB) hard drive or a storage system accessed over a network). Examples of storage media can include, for example, magnetic, magneto-optical, or optical disks, solid state drives, network storage resources such as cloud storage systems, or other types of storage media. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device, e.g., a universal serial bus (USB) flash drive, to name just a few. 
     To provide for interaction with a user, implementations of the subject matter described in this specification can be implemented on, or configured to communicate with, a computer having a display device, e.g., a LCD (liquid crystal display) monitor, for displaying information to the user, and an input device by which the user can provide input to the computer, e.g., a keyboard and a pointing device, e.g., a mouse, a trackball or touchpad. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In addition, a computer can interact with a user by sending documents to and receiving documents from a device that is used by the user; for example, by sending web pages to a web browser on a user&#39;s device in response to requests received from the web browser, or by interacting with an app running on a user device, e.g., a smartphone or electronic tablet. Also, a computer can interact with a user by sending text messages or other forms of message to a personal device, e.g., a smartphone that is running a messaging application, and receiving responsive messages from the user in return. 
     This specification uses the term “configured to” in connection with systems, apparatus, and computer program components. For a system of one or more computers to be configured to perform particular operations or actions means that the system has installed on it software, firmware, hardware, or a combination of them that in operation cause the system to perform the operations or actions. For one or more computer programs to be configured to perform particular operations or actions means that the one or more programs include instructions that, when executed by data processing apparatus, cause the apparatus to perform the operations or actions. For special-purpose logic circuitry to be configured to perform particular operations or actions means that the circuitry has electronic logic that performs the operations or actions. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what is being claimed, which is defined by the claims themselves, but rather as descriptions of features that may be specific to particular implementations. Certain features that are described in this specification in the context of separate implementations can also be realized in combination in a single implementation. Conversely, various features that are described in the context of a single implementations can also be realized in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially be claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claim may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings and recited in the claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.