The legal effect of signature comes from judicial expertise. If A denies that this signature is his promise, then partner B can ask for an appraisal of A's handwriting, and through a series of technical means, verify that this signature is signed by A himself, then A should be responsible for this signature.

Because we all know involuntary will, the name signed is definitely not a person, such as being dragged by others after being drunk. Similarly, the fingerprint can also be denied that I didn't press it voluntarily, but someone else may have drunk it, but the signature must be done on my own initiative, which can prove the authenticity of the will.

At present, many contracts are electronic contracts, and the electronic signature method of original handwriting is obviously superior to the signature method of CA digital certificate in expressing wishes, and it has been paid more and more attention. In the future, CA digital certificate may be closer to the function of ancient personal seal. There is a risk of theft, and only the original handwriting signature can represent the will.