Digital signing of web document

Question

I want our staff who have iPhones to be able to get members of the public to digitally sign a document which starts out as a Spring based web-form.

This form is only present on our intranet and only completed by our staff.

My research so far has considered a number of possible solutions:

1. Electronic wet ink signature on the screen of the phone;
2. Using the fingerprint scanner on phone to capture a specific finger of the member of the public and store it digitally;
3. PKI system;

The purpose is to prove a particular person signed a document.

1 technically possible, but doesn't count for much as it could easily be copied.

Is it possible to capture a fingerprint via the browser and javascript on a iOS device?

Can 3 be made to fit this sort of scenario?

Answer 1

If you are trying to guarantee non-repudiation of the form by the member that signed it, I would recommend to use 3.

The process could go like this:

1. A key pair (K+, K-) (public, private) is generated for the user
2. The document is signed against K-(information_input_by_user)
3. You store K+ together with your user's records in some database.
4. Fetch K+ from the database and use it to prove the user is the authentic author of the signature

Note: information_input_by_user in line 2 could be any personal information related to the user (his own input) used to authenticate him.