Direct transfer of a file between two computers on the Internet
I'm looking for a simple but direct way to transfer a file of any kind and any size between two people. If possible, having only a web browser, without having the file stored on a third machine meanwhile.
I wish to do it without requiring the end users to connect to a third server, because that way the data will flow through the machine xyz.com, possibly slowing down the transfer, and posing security risks.
I would like to avoid setting up a whole FTP server just for occasional file transfers. So far I have discovered JetBytes, Click2Copy and PipeBytes. Those web services should make the transfer easy. However the traffic goes through their servers so they are no good to what I want.
I want the transfer to be direct between the client and me. Encryption would be a nice additional feature.
I know that doing so I have to open one port on my computer, and configure a bit port redirection on my router. However, NAT traversal would be nice addition, too.
My question is:
Is there a simple way for one single end-to-end direct file transfer between two computer, avoiding third parties? (if possible, with encryption and NAT traversal)
The dirtiest way if you use *nix is to use netcat (nc) to cat the file to the remote host. But if you want encryption, you might as well use SCP/SSH.
You have to realize that if either party is behind a NAT and you don't want to setup port forwarding, then it's impossible to make a direct connection without connecting to a third-party server first. The server does not necessarily have to relay the traffic (see http://en.wikipedia.org/wiki/UDP_hole_punching) and most of them don't as bandwidth is costly.
For example, Skype will try to use many NAT traversal methods to establish a direct connection before falling back to relaying traffic through their super nodes. (Skype is a very P2P network.)
As for the account problem. I guess it's unavoidable. All methods will require some kind of configuration or setup which are usually harder than registering an account.
WebRTC-based solutions give what you need, in perhaps the simplest form. You do connect to a third-party website but that is only for getting the peers connected and not the file transfer part.
Example services:
https://www.justbeamit.com/
https://www.sharedrop.io/
EDIT: I understand this does not meet all the requirements of the OP but there is another, very usable solution: Firefox Send. Using this, you upload your file to a third-party server in an encrypted form. The service gives you a URL, which you can share with others. The URL also contains the key to decrypt the file. They can then download the file. The file is automatically deleted after a set number of downloads or after 24 hours. The server never sees the key and so cannot decrypt the file. The advantage in using a third-party server is that the sharing party and the downloading party do not need to be online simultaneously.
You can sync files between remote computers using a rsync. This utility is available for Windows in cygwin, or you can install it with the pre-packaged cwRsync.
I'll leave my previous answer here intact, but given recent revelations about the NSA, I would no longer recommend Skype for secure file transfers.
You can send a file directly to another person using Skype. Skype sometimes even works when both users are behind NAT. If you are saavy enough to open a port on your router, doing so will increase the likelihood of a negotiating a direct connection.
More broadly, many chat programs include a file sharing/sending mechanism. Most don't supply encryption by default like Skype. But as long as you and your recipient have the same chat client, you have a "simple tool" for sharing files.