For an open source project I'm currently working on, I need people to trust a website. Basically, the user would write "foo" on his phone. It would go on the website which would take the message "foo" and send it to a server running on this user's PC. I want people to be sure that the server did not change "foo" into "bar". I know I'm not malicious but potential users don't know it so I need them to trust me.
There are 2 possibilities. The first one is to use cryptography. The user would encrypt on his phone "abc" and the server running on the user's PC would decrypt it. But it's cumbersome for the user (he would need to encrypt it in another app). The second possibility would be to convince the user I'm not malicious by showing him the code running on the server. I can show the code on Github easily. The question is how can we ensure that the code running on Github is the same as the code running on Heroku?