simple command line encrypted password storage
step 1. modify test.php to your needs (change mysql server username, password, and dbname (and host if necessary).
step 1.5. modify backup.php to your needs
step 2. import sql setup file to your database.
step 2.5. setup cron script to call backup.php every few days
step 3. setup local C# client (point to http://yoursite.com/)
step 4. done, DO NOT LOSE ENCRYPTION KEY, IT IS UNRECOVERABLE!
All encryption / decryption is done client side, which prevents MITM hacks and database leaks. However, this means that the users security is entirely in their hands. If they pick a bad password, their database can be decrypted. If their computer gets hacked, their passwords are gone.
Encryption standard is AES-256 and HMAC. username, password, and site are encrypted and POST'ed to the PHP file (test.php), and the PHP file handles the request and does what is required (select from db, insert to db, etc).
do not use this for serious purposes, everything is stored in plaintext as of 11/5/19, and communication between client and server is in plaintext
edit:
as of 11/6/19, all passwords are stored using AES then HMAC, and all the decryption is done on the client side. Client and server communications are still plaintext, but this shouldn't cause as much of a problem.
I am not responsible for damage / losses caused by failures of this program. Read the license.