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Combining TEE and Blockchain

Combining TEE and Blockchain
This blog post will discuss the latest development in improving blockchain - using Trusted Execution Environments (TEE) to increase scalability and confidentiality.

Blockchain Background

For those who aren’t familiar with blockchain, here is a quick rundown of what is blockchain. 
Blockchain decentralizes and distributes data across a network of computers, functioning as distributed
ledgers. Each participant, or node on the network, has a copy of the stored data in a secure, distributed,
and shared database which eliminates the need for a centralized authority. Any changes or additions to
the database must be validated by the collective members before the entire network is updated. This
provides an unchangeable record and ensures data quality and integrity. 


Users are able to submit transactions, which are collected as a block and the network then distributes
and verifies the blocks and appends them to an irreversible chain.  Additionally, blockchains use
cryptographic signatures to ensure accuracy and create an immutable - or unchangeable - ledger. 

How does TEE play a role in this?

Normally, transactions are processed on the blockchain, which presents a scalability challenge
because every node in the chain needs to be informed of the transaction and update its copy of the
distributed ledger. This system ensures that transactions are transparent and the integrity is solid, but
it reduces the throughput - the speed at which transactions are processed - as well as confidentiality. 
A solution was proposed by Hyperledger Avalon, a fairly new Hyperledger project, a month ago.
The solution or at least the middle ground for this problem lies in performing some operations
“off-chain” using a combination of or simply one of the following: TEE, MPC (multi-party compute),
and ZK (zero-knowledge proofs). Due to the scope of this blog post, the latter two components will
not be discussed. The following image shows the structure.
When a transaction needs to be executed, the requester creates a Work Order which is passed into the
Trusted Compute Service where a worker performs the task. Afterward, a receipt is created which goes
to the chain.

 Intel SGX capabilities such as code verification, execution isolation, and attestation verification can
help provide a reliable link between the main chain and off-chain compute resources. SGX’s prevention
of code modification or data disclosure allows blockchain data to be protected through encryption until
required for a transaction and verification of correct computation to be performed. Additionally, attestation
is important because trusted worker processes need to be vetted and cataloged within a registry that
includes their attestation information. 

Possible Drawbacks

A number of potential roadblocks have been considered.
  1. Centralized remote attestation service
    • To do a remote attestation, you must contact Intel’s cloud service
    • Not really decentralized
  2. SGX is disabled by default
    • Not a problem for computer-savvy people, but what about non-technical users of blockchain? 
    • Many mobile devices don’t have SGX
  3.  Unclear licensing and terms of use for SGX by Intel 
    • Intel themselves have supported Hyperledger Avalon, but it is unclear how they will respond to future business

References


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