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Self-Sovereign Identity – The Nash Equilibrium Point of the Personal Identity Information Game

1 Privacy or convenience is a question

Under the COVID-19 impact last year, in China, health codes have become the credentials we use frequently for general access and it does make life convenient for us. A health code is a QR code within Alipay or Wechat applied from verified data sources like mobile-phone carriers or health institutions etc, indicating the level of health risks. Because of the system isolation between different areas, a large amount of personal information, including names, ID numbers, contact information, and health status, etc. are repeatedly collected by local governments and used to authenticate independently later. Some of the information may not be useful for getting into places, but limited by technology, we cannot keep the balance between privacy and convenience. This reminds us that repeated authentication is often used because the personally identifiable information is distributed in different systems, and privacy breaches can occur.

This happens, not only in extreme situations like COVID-19, but also in everyday life and business activities. User privacy has been widely breached across the Internet. For example, Facebook granted Cambridge Analytica to access the personal information of 50 million users, and Equifax was hacked into disclosing the personal information of 147 million users. Both are infringed on user rights including the right to process data, the right to know, the right to be forgotten and data security commitment. User privacy data breaches not only affect individuals, but also result in huge fines to companies, and even spread the consequences into the entire society.

Figure 1 User privacy breaches

2 SSI is the answer to this question

What if we want to keep privacy and convenience in COVID-19? The SSI(self-sovereign identity) technology exactly fits in here.

The main part that constitutes SSI is the decentralized identifier(DIDs) system. DID is the unique ID of an individual in the digital world and cannot be revoked by any person or organization other than the individual. However, an identifier alone has no practical use. It needs to be complemented by another technology, verifiable credentials. Verifiable credentials are personal information statements associated with DIDs, which have been verified by a trusted third party to be authentic and valid, and can be verified in a digital way. For privacy purposes, verifiable credentials abide by the principle of minimal data disclosure, for example, a verifiable claim can only contain a “yes or no” assertion. If one wants to go to a bar, there is no need for him/her to show the full personal identity information upon arrival. Instead, if he/she presents a verifiable credential containing the assertion of “21 years old and above”, the establishment can determine whether to admit him/her after verifying its validity. With verifiable credentials, personal profiles created on DIDs can be gradually improved, and the power of SSI can be properly unleashed.


Figure 2 The roles SSI and verifiable credentials play in protecting personal privacy

Back to the health code scenario. Users may apply for health credentials from institutions responsible for verifying their health conditions. Such credentials only contain a statement of their health condition. Once the application is successful, the credential is stored on the user’s device, owned and controlled by users like real life credentials, any verification needs authorization and users can also combine several verifiable credentials into one. At access check, the user may choose to present this credential which bears the information of “yes” or “no” only. Other information of the user is not disclosed, and the authenticity of this credential is verifiable so that nobody can sneak through with fake credentials. More importantly, there is no need for us to submit personal information repeatedly! The SSI technology not only allows users to control their identities, but also helps users control the level of privacy disclosure.

Figure 3 The interaction between DIDs and verifiable credentials

3 Conclusions

A silent war is ongoing between users and companies over the control of data. They are having a pig and piglet game. If the user does not assume any responsibility but can enjoy the free service, all the costs are borne by the company, then it is easy to produce a free-rider problem. On the other hand, Companies using users’ personal data without restriction can seriously infringe their rights. So, we need to shift the strategy to drive the company and the user to bear a certain cost, which is just like putting the trough closer in the game. In this manner, a  blockchain-based SSI system can help users to control their identity, and also enables companies to get the least available personal data on demand, so the game between users and companies does not need to change the strategy unilaterally, which reaches the nash equilibrium point.

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