I can write your name as the sender on a physical letter and send it, and I can do the same thing with an email.

There, conceptually it's explained, to anyone who has any concept of what "writing" is.

I think the difference is people can envision how someone can write a fake sender on snail mail but they can't envision how it's done on email -- they need to log in first, after all.

(Also I wonder if using the word "signature" only makes it harder to explain. Like, trying to explain to someone how an analog signature proves your identity. Because, well, it doesn't.)

An analog signature does "prove" your identity. Not very well, of course - the amount of effort to forge it is much less than a digital signature - but that's a question of degree, not kind. They are still easier to verify than they are to forge. I think the metaphor is very useful.

It also neatly explains the concept of key sharing, which seems to present some pedagogical difficulty for some reason - you can sign your letters all you want, but if I've never seen your signature before then it doesn't actually prove anything.

Public key = knowing what your signature looks like

Private key = the muscle memory required to create a signature

What you are saying, put into more provocative words: email world be safer now if, from the beginning, every email client had a big, friendly button "send from different address". In the years of earthly mass adaption it would have been colloquially called "the Bill Gates button". It certainly would not be hard to explain the value of signatures in that timeline.

Well I don't know if it would be safer per se... I imagine you'd probably want some USPIS enforcement for that to happen, otherwise it might end up like phone calls (given it seems people understand caller IDs are spoofable and yet it's as big a problem now as it's ever been). But yes, it could've made it potentially easier to explain.

> they can't envision how it's done on email -- they need to log in first, after all

By now every single email user with an email address that has been exposed to the internet has received untold amounts of spam emails with their own address spoofed as the sender. The only question is if they've ever noticed it.

Probably not, if they use any decent email provider 99% of spam gets correctly filtered and you never really see it unless you look in the spam folder, which most people don't anyway. Also, I don't think I ever received an email with the sender as one of my email addresses.

Not really. I get a steady stream of replies to me from ignorant users who reply to "Joe job" spam, as do everyone I know. It's the most common way someone thinks "I've been hacked" when they get the fallout from one of these "Joe jobs"

My email client (geary) makes it pretty easy to add and send from aliases. If I ever need to explain this to someone, I'll keep a demonstration of this in mind :)

> and I can do the same thing with an email.

This wouldn't pass most spam filters today, thanks to stuff like DKIM: https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail

But if I can get a domain that looks almost like yours and send an email from there, what good is DKIM then unless someone's paying real close attention?

Your new domain will look suspicious to any bigger spam filter (e.g. Gmail's) and therefore you have to be really careful with the content of your email so that it gets through.

But I agree that this is rather intransparent for the user. What we need is a warning like "You have never received an email from this domain. Do you want to trust it?" and something like the Extended Validation Certificate for companies (does something like this already exist?). Not PGP though.

A lot of people would still fall for that too unfortunately. And ultimately people don't know that you can even do that. They see as authenticating oneself as proving their identity.

Authentication does prove identity, to their mail service, not to the recipient.

But they are right in one sense: it's their mail provider's job to provide the signing infrastructure.

But customers have to know they need it and demand it