Build an End-to-End Encrypted File Sharing Web App

Traditional file-sharing apps may encrypt data during transit but store it unencrypted on the server. End-to-end encryption ensures that even the server can’t access the file contents, providing true privacy for sensitive data transfers.

The system ensures that only the sender and recipient can decrypt the file. All encryption is handled on the client side using cryptographic libraries, and shared links contain decryption keys or passphrases securely transmitted to authorized users only.

When a file is selected, the client-side app encrypts it using AES or RSA before uploading it to the server. The server stores only the encrypted file. The recipient gets a shareable link containing a decryption key or is prompted for a secret passphrase to decrypt the file upon download.

• User uploads file → file is encrypted in browser → uploaded securely.
• Server stores encrypted blob without knowing the original content.
• Shareable URL is generated, optionally with embedded key or separate password.
• Recipient opens the link → decrypts file in-browser → file is downloaded.
• Admins or users can control expiration, max downloads, or file retention duration.

• Web Crypto API – MDN Docs
• crypto-js Encryption Examples
• Secure File Upload Handling in Flask
• Client-Side Encryption with libsodium.js
• Project Inspiration: Firefox Send (archived)