I am searching for a convenient way to securely transfer a single file from a desktop computer A to a mobile computer B. A runs Linux, B runs Android. By "securely" I mean that:
a) a file must not leak to a third party and
b) A and B do not trust each other. I specifically ask how to transfer a single file.
c) It should be as easy as picking that file in a file manager
I expect non-regular transfers, in other words, a transfer is usually the first transfer between A and B, and they were not configured for this transfer before. A and B are connected to the internet. (Well, what is not connected to the internet nowadays?) But:
d) at least one computer has no global IP address or
e) both have no global IP address.
Consider the cases (d) and (e) separately.
Some schemes I can think of.
- B is connected as a MTP storage. Then even the internal flash memory of B is accessible. Contradicts (b).
- Wired or wireless Ethernet requires configuring a network, then a network server of some sort (for example, FTP, HTTP), then an authentication scheme. This scheme is bad on (c).
- In principle, a connection via a cable or an optical link does not require authentication because I see what device A or B is connected to. So it fits (c) better than a wireless connection. But I don't know how to exploit a cable without Ethernet or what program can transfer a file via an optical link.
- Moving a flash memory device between A and B. Wiping the whole partition containing the file by the Unix program "shred" satisfies (a). Low on (c).