Programming language: Go
License: MIT License

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brew install ZinoKader/homebrew-portal/portal


Either get the latest release and install it manually, or run

curl -s https://raw.githubusercontent.com/ZinoKader/portal/master/scripts/install.sh | bash

if permission denied for moving the files to /../bin, replace " | bash" with " | sudo bash" (the script is in the repo, so you can check it out before you blindly trust in it!)

The application

portal is a fast and secure file transfer utility for sending files from one computer to any other computer. All communication beyond the initial client handshake is encrypted. If the sender and receiver can reach each other directly, the file transfer involves no servers. Otherwise the file transfer goes through a relay server which facilitates the connection, but sees none of the data.

Sending files and folders

The file transfer starts by invoking the command from the sender side:

portal send <file1> <file2> <folder1> <folder2> ...

The application will output a temporary password on the format 1-inertia-elliptical-celestial. The sender will communicate this password to the receiver over some secure channel.

Receiving files and folders

The receiver would then issue the command:

portal receive 1-intertia-elliptical-celestial

The two clients will connect to each other and transfer the file(s)/folder(s).

Extra: hosting your own rendezvous/relay server

To make connection establishment possible, portal makes use of a rendezvous server. By default, a rendezvous server hosted at Digital Ocean is preconfigured, so you do not need to do anything. If you would like to host one on your own, build the server and start it with:

# specify port with -p or --port
portal-rendezvous --port 80




portal provides:

  • End-to-end encryption using PAKE2 to negotiate a shared session-key
  • Direct transfer of files if possible (e.g. sender and receiver are in the same local network)
  • Fallback to a TURN-server (rendezvous-relay) for file transfer if the sender and receiver are behind NATs in different network
  • Parallel gzip compression of files for faster and more efficient transfer

Technical details

The connection between the sender and the server is negotiated using a intermediary server called portal-rendezvous. The portal-rendezvous server is used to negotiate a secure encrypted channel while never seeing the contents of files nor the temporary password.

The communication works as follows:

  • sender application connects to rendezvous-server
  • rendezvous-server allocates an id to the sender and sends over websocket to the sender
  • sender outputs the password to the terminal, hashes the password and sends it to the rendezvous-server
  • receiver hashes the password (which has been communicated over some secure channel) and the sends it to the rendezvous-server
  • When both the sender and the receiver has sent the hashed password to the rendezvous-server the cryptographic exchange starts, during which the rendezvous-server relays messages from the sender to the receiver or vice versa
  • Once the cryptographic exchange is done, every message sent by the sender and receiver is encrypted, and the rendezvous-server cannot decrypt them
  • Now two things can happen:
    • Either the sender and receiver are behind the same NAT, in which case the file transfer will be directly between the sender and receiver. In this case, the connection to the rendezvous-server will be closed
    • If they are not behind the same NAT, the transfer will fallback to go through the rendezvous-server which will continue to relay encrypted messages until the file transfer is completed

Motivation, team

This was initially a project made for the course IK2218 Protocols and Principles of the Internet. We often used similar tools in our day-to-day and wanted to make our own!

Project members:

  • Zino Kader
  • Arvid Gotthard
  • Anton Sederlin

Software used