jojo2357/PhoneHome

Connects two devices over local network for ease of ssh

Remote Home

I am at a place that has a geographically large WiFi network. As such, I sometimes end up separated from my two computers, and find myself in need of files from the other laptop.

Since I usually leave them on and connected to the network, I was able to write the scripts in this repository to rapidly connect the two physically separated laptops.

These scripts are not miracles, they just allow for a streamlined connection from one machine to the other via ssh. This is NOT remote desktop, and recommended to the terminally ill advanced out there.

This does NOT support windows, but I imagine a simple translation from bash to batch would we sufficient.

Usage

This process is slightly involved. Requires two machines, and each step to be completed on both machines before moving to the next step.

0. Install and enable ssh server, create ssh key

sudo apt install openssh-server
sudo systemctl enable ssh
sudo systemctl start ssh
ssh-keygen -t rsa -b 4096

1. Copy ssh key to other device. This assumes they have the same username which will make everything easier.

# if you know your ip, you can replace the $() with that ip
ssh-copy-id $(whoami)@$(ifconfig | grep -Eo 'inet (addr:)?([0-9]*\.){3}[0-9]*' | grep -Eo '([0-9]*\.){3}[0-9]*' | grep -v '127.0.0.1')

2. Disable password authentication. This will force ssh to use the keys we just created. (Not required, but highly recommended especially if this is not your private home network)

# We need to uncomment and change PasswordAuthentication yes to no
sudo nano /etc/ssh/sshd_config
# restart server
sudo systemctl restart ssh

3. Configure scripts.

# replace <homemacaddress> with the OTHER machine's mac address
echo <homemacaddress> > ~/.homemac
echo $(iwgetid -r) > ~/.homenet

4. Phone home!

./phonehome

Extra steps

You can and should add the folder with these scripts to your path. I will not tell you how to do that since you may have your own way.

How it works

These scripts work in the following way. They first attempt to find out the IP address of the other machine and verify that the MAC and IP agree:

flowchart TD
  Entry[Begin] --> Mac[Read Mac Address]
  Mac --> Net[Check Valid Home Network]
  Net --> CachedHome{Is Home IP Cached?}
  
  subgraph CachedNo[No]
    Pass[Skip]
  end
  subgraph CachedYes[Yes]
    Ping[Ping Cached Home IP] --> Pingresult{Did ping succeed?}
    
    subgraph PingYes[Yes]
      Pingmacresult{Did respondant have correct MAC?}
      subgraph MACYes[Yes]
        MacFound[Cached IP Valid! Proceed to next chart]
      end
      subgraph MACNo[No]
        MacUnfound[Cached IP invalid. Pass]
      end
      
      Pingmacresult --> MACYes & MACNo
    end
    subgraph PingNo[No]
      Pingtopass[Skip]
    end
    Pingresult --> PingNo & PingYes
  end
  
  CachedHome --> CachedYes & CachedNo
  
  subgraph FindIP[No valid cached IP]
    ScanNetwork[Scan network for stored MAC] --> ScanQuestion{MAC Found?}
    ScanYes[IP Found! Write to cache and proceed to next chart]
    ScanNo[Host offline, bye!]
    ScanQuestion --> ScanYes & ScanNo
  end
  
  CachedNo & MACNo & PingNo --> FindIP
  

Once that has happened, the connection and handshake happens

flowchart TD
  Entry[Home IP] --> QuestionInSSH{In ssh?}
  
  subgraph SSHYes[Yes]
    SSHPass[Pass]
  end
  subgraph SSHNo[No]
    CopyFyles[Copy current machne's IP to remote ip cache file]
  end
  
  QuestionInSSH --> SSHYes & SSHNo
  
  SSHYes & SSHNo --> MakeSSH[Connect terminal via ssh and exit for the user to use]

Tada! Magic.