Saturday, August 10, 2019

How to run Fossa Guard on Android

The guideline describes how to run a free version of Fossa Guard extension V0.4.6+ on mobile Yandex browser on Android platform to enable end-to-end S/MIME encryption on top of Gmail on your mobile.

On your Android mobile:
  1. Install and run the Yandex browser
  2. Navigate to Chrome web store and find Fossa Guard free extension
  3. Click 'Add to Chrome' and then 'Add Extension' to install the Fossa Guard extension. 
  4. Navigate to Fossa Guard extension via Yandex browser 'Extensions' menu. 
  6. Switch to Portrait mode for convenience (work on responsive UI is ongoing).
  7. Click 'Login to Extension' to associate your Google account with Fossa Guard - a new tab should appear in Yandex browser with Google authentication. 
  8. Navigate to this tab using Yandex tabs menu. Authenticate to corresponding Google account (we use
  10. Allow Fossa Guard to use requested permissions. On success, Google authentication will be auto-closed. 
  11. Navigate back to Fossa Guard tab to check the settings.
  13. At this point you have 2 options: Import your backup personal Certificate and key OR Enroll free personal certificate from Fossa CA.
  14. Fossa certificate enrollment is based on the local key pair generation in your Yandex browser without sharing the private key. Certificate Signing Request (CSR) to sign certificate by Fossa CA is initiated using SSL connection over HTTP. Click 'Enroll Fossa Certificate' to initiate the flow. 
  16. To establish a secured SSL connection over HTTP navigate to ' Server', log in using the same Google account and copy the one-time shared secret.
  18. Paste shared secret at Fossa Guard extension and proceed with the enrollment. 
  19. Once signed certificate is received back from Fossa CA, the extension asks for the strong passphrase to protect your private key (which stays within your browser all the time). 
  20. Your private key will be saved into the local Yandex browser storage within your phone and will never be compromised outside it.
  22. Once the enrollment is done you should get an invitation to start secured mailing with Gmail. 
  24. Navigate to the mobile web version of Gmail
  25. Ensure that you logged into Gmail with the same Google account (we use  
  27. You should notice the fancy green button at the right top with 'S/MIME' label. Click it to compose S/MIME email
  29. Type 3 letters of your recipient address and you should get a list of corresponding contacts for selection. Fossa Guard automatically checks if the addressee has got Fossa certificate and indicates it by the green color of the email pill.
  31. Once you finished with composing S/MIME message, click 'Send S/MIME' and it will be sent using Gmail API and should appear in Sent folder marked by the corresponding label 'S/MIME'
  32. Click on S/MIME labeled email to check the details and you'll discover 'smime.p7m' attachment which is unreadable for Google robots and the notification from the extension that this email was composed using S/MIME. 
  33. Click 'View Content' and you'll be requested for the passphrase to access your private key (locally within your current browser session).
  34. Once you provide the correct passphrase the extension will decrypt the message and show you in a dedicated window.
  35. If the email address of your Gmail account does not correspond to the email address of Google account associated with the extension you'll the notification to use the same account. This is the identity check Fossa Guard makes to secure access to the private key.


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