EMAIL ENCRYPTION FOR ANDROID . Invite bids from Europe/US ONLY

I need an email encryption and decryption app. Bid only if you are an encryption expert and know android inside out. ABSOLUTELY NO BIDS FROM INDIA PLEASE. Need design and code. In app payments required. screen 1: login/signup/ recover password screen 2: signup : email, password, first name, last name screen 3: email confirmation screen 4: main screen: has inbox, when user clicks an email, it is decrypted and displayed in message area. He can click reply and compose, and when SEND is clicked, first encryption happens and then message goes. Compose new email button creates new email, and SEND button encrypts. INVITE button lets user invite other users to join the site. If user sends an encrypted email to a person who is not using the app, he will have a link in the email to download the app and join, and the encrypted message that he cannot read. Must implement on firebase. Admin app also needed to administer the membership. ENcryption is done on user phone, decryption is done on user phone. FIrebase server only to relay the encrypted message. Once message is read, it is deleted from server immediately. Not for Indian programmers, sorry. Please bid only if you are an expert. This is for US/ Europe educated programmers. Budget 300 max