opensend/README.md

OpenSend

Send files between systems quickly and securely

Usage

Receiver

• Use opensend -r to start the receiver

Sender

• Use opensend -s -t <type> -d <data>
• type can either be url or file
• If type is url, data should be a URL
• If type is file, data should be a file path
• Example: opensend -s -t url -d "https://google.com"
• Example: opensend -s -t file -d ~/file.txt

Building

• This project uses go modules, so building is easy
• First, go 1.14+ must be installed (use buster-backports on debian)
• Then, run make inside the project's directory.
• This will get the dependencies and compile all the files.

Installing

To install, simply follow the building instructions and then run

• Linux: sudo make install
• macOS: sudo make install-macos

Using on iOS

Opensend can run on iOS using the iSH app.

• Install go using apk add go
• Clone this repository
• Run make
• Use opensend as normal, but skip device discovery
  • Device discovery does not work properly in iSH due to Alpine Linux
  • When running receiver, add --skip-mdns
  • When running sender, add --send-to <IP>
  • This applies bidirectionally
• Known issues
  • Opensend takes a while to become ready on iOS

Ports to whitelist

• TCP 9797 for key exchange
• TCP 9898 for file transfer

How does it work?

OpenSend uses a combination of 2048-bit RSA and AES GCM encryption. This is accomplished using golang's crypto/rsa and crypto/aes libraries. First, a shared AES key is generated. Then, an RSA keypair is generated. The RSA public key is then exchanged using TCP and golang's encoding/gob library. The AES key is encrypted using the RSA public key of the receiver. This key is then saved to a file. Next, the shared AES key is used to encrypt all the files in ~/.opensend. To send the encrypted AES key, the sender first needs to discover the receiver. This is accomplished using zeroconf. After that, the sender starts an HTTP server with some custom functions to send the file index and key. The receiver gets the index, files, and encrypted key from this server. Once it gets all the files, it sends a stop signal to the server and decrypts the shared key using its RSA private key. The resulting AES key is then used to decrypt all files in ~/.opensend.