Ever thought of encrypting uploaded files in the web browser before they hit the server? Most web browsers nowadays offer encryption modules via the Web Crypto API for the encryption itself, but we’ll soon see that this isn’t enough. What about the correct cipher modes? How can we ensure confidentiality, integrity and authenticity? What about big files and limited memory availability. In this talk, we’ll cover the following topics:

• Issues you’ll face when implementing end-to-end file encryption in the browser
• The crypto basics behind file and metadata encryption
• The Web Crypto API
• The FileReader API for chunked uploads
• The ReadableStream API for chunked downloads
• Service Workers and how they’ll help us
• Browser compatibility of the mentioned APIs
• What we can do to support older browsers
• The hardest part: key distribution