Secret letter electronic contract signing service supports two signature methods: electronic signature and digital signature. Although electronic signature only verifies the user's e-mail address, according to the electronic signature law of western countries such as Britain and the United States, and the widely adopted practice that personal signature can represent individuals and representative units in the west, electronic contracts signed by electronic means have legal effect. Therefore, at present, mainstream foreign manufacturers, such as DocuSign (an electronic signature service) and Adobe Sign, all use electronic signatures to sign contracts online. According to the provisions of China's Electronic Signature Law, if all contract signatories agree to sign an electronic contract by electronic means and agree with its legal effect, then signing a contract by electronic means is also legally effective, which greatly facilitates the signing of an electronic contract by both parties in China and the West with the same verification method.

Because the traditional paper contract signing method in China requires the real identities of all parties and the red private seal and official seal, the clause of reliable electronic signature has been added to the electronic signature law in China. If an electronic contract is signed with a legal CA digital certificate, it is not only legally effective, but also equivalent to the handwritten signature and company seal of a paper contract, similar to the qualified signature in Europe. That is to say, China's electronic signature law not only absorbs the advantages of convenience and rapidity of British and American electronic signatures, but also absorbs the advantages of attaching importance to identity authentication in Europe, making China's electronic signature law more universal and practical.

Although almost all countries in the world recognize the legal effect of electronic signature, and because PKI technology perfectly solves the problem that the real identity of the signer and the signature picture of the old electronic signature can not be verified, we strongly recommend that users sign electronic contracts in digital form, which is also a common way adopted by major electronic contract signing service providers in China.

The electronic contract documents signed by Secret Letter APP adopt Adobe's trusted PDF signature certificate and SM2 signature certificate that conforms to the state secrets, realizing double certificates, double signatures and double timestamps, technically realizing the global trust of the signed contract documents and the compliance of state secrets, and ensuring that the signed electronic contract has legal effect on a global scale.