alt Hacker NewsNice design, but that's the kind of functionality that's best integrated within a chat or videoconferencing application, since within a conference you can be pretty sure that you send the file to the right person.
For a demo, go to <https://galene.org:8443/group/public/hn/>. Login twice in two different browser tabs (leave the password field empty). Click on the username of your partner, and choose Send file.
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In modern conferencing applications, users are not connected with each other, they are connected with a central server.
Transferring files shouldn't involve that central server, so you'd need to establish a direct connection between the users, and with network topologies those days, it will most likely require a relay between the two. It's not great.
I used your demo. It does not do what you say that it does.
I opened a tab and signed in as "username".
Then I opened another tab and signed in as "username" there, too.
Thus a shared chat exists with two users named "username".
Whatever this is, it is not the path of disambiguation.
I don't agree with this.
No, it's best to write the data on a USB stick and see the person in real life. Ask for ID and do a retina scan. Then you can be pretty sure that you give the file to the right person. Make sure to cryptographically sign the data so the recipient can be sure it's you.