The original note, as written at the time
A device for only reading, sharing and signing, stamping or authenticating official sensitive documents. For all those who worry about sharing signed and stamped documents.
Ongoing development
A device for only reading, sharing and signing, stamping or authenticating official sensitive documents — for everyone who worries about circulating signed and stamped papers.
The single-purpose device is the idea, and it is the right shape for the problem. A signed document today travels as an image on a phone that can also edit images, and the recipient has no way to know whether what they received is what was signed. Every party knows this and proceeds anyway.
A device that can only read, share and sign removes the ambiguity by removing the capability. It cannot alter, so an alteration is evidence that the file left the device. That is a weak guarantee technically and a strong one socially, which is often the more useful kind.
The function that matters most is verification rather than signing. The recipient needs a way to check that the signature is the one that was placed, and to see what was covered by it, in a form a clerk can understand.
The hard problem is proliferation. A document system that requires a special device is a system that requires everyone to have one, and the people who most need to receive a signed document are the people least likely to own a gadget. So the verification side must work on an ordinary phone, even if the signing side does not.
The second problem is the stamp, which in our practice is a physical object with a person’s authority in it. A device that reproduces a stamp is a device that can forge one.
Make the signature checkable by anyone, and keep the stamp physical.