Even amid a global travel standstill due to the coronavirus, more than 17 million people travelled between Macau and China’s southern Guangdong province since May.

This is thanks to a mutually recognised QR health code system using a crucial piece of technology: blockchain.

Blockchain technology is seen as a secure way to transfer data as it stores records in a network of computers instead of a centralised system. Each new record is linked to previous ones, making it extremely difficult for anyone to make changes.

The mainland China-Macau health code system, based on technology by Chinese open-sourced blockchain platform FISCO BCOS and WeBank, a fintech developer backed by Chinese internet giant Tencent Holdings, provides a solution to a major challenge to cross-border travel, FISCO BCOS said in a press release on Monday.

“Health authorities in Chinese mainland and Macau need to verify the health information submitted by users crossing the border and yet they are not supposed to exchange data directly with each other to stay in compliance with their corresponding regulations,” the blockchain platform said.

The health code system uses blockchain to encrypt the identification and personal health information of travellers, storing it in a consortium blockchain network which grants access only to authorised organisations.

This way, health authorities on both sides are able to verify whether travellers are in good health and have been in contact with any known Covid-19 cases without actually accessing personal data, thus complying with privacy regulations on both sides of the border that prohibit the direct exchange of such information.

With the code and valid negative coronavirus test results, Macau travellers are now exempt from a 14-day quarantine when entering China. Chinese travellers from outside Guangdong province can also participate in the system to travel into Macau without quarantine requirements as long as they allow Guangdong authorities to access their data.

“The whole process does not involve transmission of data between back-end platforms,” said Fan Ruibin, head of blockchain technology at WeBank. “The original data is still stored in the local authority’s data centre.”

The technology “greatly improves the efficiency and accuracy of information verification across borders” and saves travellers the trouble of filling in personal information repeatedly on different platforms, FISCO BCOS said.

The average time of setting up the mutually-recognisable health code for the first time is 100 seconds and it takes less than 3 seconds to repeat the procedure thereafter, according to the statement.

Technically speaking, the system allows “both authorities to recognise a person’s health conditions through asymmetric cryptographic technology,” which uses a pair of related keys to encrypt and decrypt a message and protect it from unauthorised access or use, said Gao Chengshi, a cryptography expert and a member of the Blockchain Committee of the China Computer Federation.

“The technology itself isn’t complicated, and can be easily introduced to other countries and regions as long as the authorities are willing to conduct such mutual recognition of health identities,” Gao said.