10 May Update: the app was suspended last night by Wechat and then available at noon today. But now it has been suspended again.
The 1st Wechat Blockchain applet is called “xiaoxieyi” or “Mini Contract”.

WeChat applets are lightweight applications that run within the WeChat environment. WeChat applets are more flexible than public accounts because many features that are not available for WeChat public accounts are available in applets. Although applets are smaller than dedicated apps, applet developers can still profit by leveraging the large user base of WeChat attract a number of service providers.- quora

The applet is very simple:

1. Enter the title and content of the contract,
2. Choose whether to encrypt the contents,
3. Pay 3 yuan of service fees

Then an agreement will be generated. Party A, the creator of the contract, may send it to Party B. After Party B agrees, the agreement will be written on the Ethereum network and became irrevocable.

Screenshot of contract created via the wechat applet

According to the official page, in just 3 minutes, you can create an irrevocable contract with unique WeChat ID and blockchain technology. The applet can ensure that the content is authentic and reliable and both parties have reliable identities. Service like senior lawyer and preservation of electronic evidence preservation could be provided at any time.
Stored in the blockchain, the agreement is certainly not changeable, but how to determine the authenticity of both parties to the agreement? The small agreement borrowed the power of WeChat. When the contents of the agreement were recorded on Ethereum, a signature based on both the WeChat ID and the session key was attached.

The contract applet will read the WeChat IDs of Party A and Party B, which is a fixed identity as it is usually bundled with a lot of personal information. Wechat ID is highly secure and verifiable. In addition, the session key refers to the timestamp when Party A creates the contract and when Party B agrees with the contract. The applet then sums up these four values, encrypts them with md5, and writes the generated signature to the Ethereum blockchain.

The verification method is very simple. According to the law, we can find WeChat to get these four values when necessary and re-encrypt it once. If it is consistent with the contents of the blockchain, this agreement is true.

The explanation may sound complicated, but the experience of the applet in the front end is very smooth and clearn. You don’t need to buy Ethereum to pay for the transaction. You can use WeChat pay in CNY directly. The applet will finish the on-chain transaction in the background. The whole process was completed in Wechat environment.

By searching the given tx id, one can find the applet is attached to the following address.
0xc6cda87c2f9fb4d00d40bd518a847a6690aa1988
So far over 300 transactions has been created.

Wechat is biggest social tool among Chinese and has 1 billion active users by March 2018.