Using "OpenVPN for Android" to Redirect all Local Traffic from my Phone to a Local Packet Filter Application

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peurpdapeurp
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Joined: Thu Jul 18, 2019 6:51 pm

Using "OpenVPN for Android" to Redirect all Local Traffic from my Phone to a Local Packet Filter Application

Post by peurpdapeurp » Thu Jul 18, 2019 6:59 pm

Hello,

I am working on an Android project which requires me to intercept traffic from a particular application, modify that traffic, and then send it out again.

One solution would be to modify the application, but I want to avoid that if possible (my client does not want that).

Therefore, I thought one way to do this would be to have a VPN service capture all of the traffic from all of the applications on the Android phone, intercept and modify the traffic from the particular application I need to change, and let all other traffic pass through without modification to their original destinations.

I was thinking that OpenVPN could be a possible candidate for accomplishing this. In particular, I was reading through the HOWTO page and came to this page:https://community.openvpn.net/openvpn/w ... yMiniHowto

I thought the above page fit my use case, as I want to keep things as simple as possible. I thought that in this case, the "client" would be my Android phone and all the applications on it, and the "server" would be some kind of OpenVPN server I could set up locally on my phone to intercept and potentially modify traffic before sending it to its original destination.

However, looking at the configuration files on that page gave me second thoughts:

Client configuration file:
remote myremote.mydomain
dev tun
ifconfig 10.8.0.2 10.8.0.1
secret static.key

It seems that in the configuration files, there's no way to specify ports, which made me wonder if I was misinterpreting how I could use OpenVPN. For example, for my use case, I guess I would set both the IP addresses in the configuration file to 127.0.0.1, but that just doesn't seem to make sense, and so I think I am approaching this wrong.

Could anyone out there point out to me if there is a flaw in the logic I have been using so far? Am I misunderstanding how to use OpenVPN? Is OpenVPN actually able to do what I am trying to make it do?

Thank you very much for any help.

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