How to Share Files Securely: A Complete Privacy Guide
Step-by-step guide to sharing sensitive files without exposing your data to third parties. Covers client-side encryption, secure link generation, expiring downloads, and zero-knowledge file transfer services.
Key Takeaways
- When you upload a file to a conventional cloud service, the provider can access your data.
- The safest approach encrypts files in your browser before any upload occurs.
- For simpler scenarios, a password-protected ZIP or 7z archive provides decent protection.
- Even encrypted files can leak information through metadata β file names, sizes, timestamps, and EXIF data in images.
- For truly private sharing, encryption must happen before the file leaves your device.
The Problem with Standard File Sharing
When you upload a file to a conventional cloud service, the provider can access your data. Their servers decrypt, scan, and index your files for various purposes. Even with HTTPS protecting the transfer, the file sits unencrypted on their storage. For truly private sharing, encryption must happen before the file leaves your device.
Client-Side Encryption Workflow
The safest approach encrypts files in your browser before any upload occurs. The encryption key can be embedded in the URL fragment (after the # symbol), which browsers never send to the server. The recipient's browser extracts the key from the URL and decrypts locally. The server only ever sees encrypted bytes.
Step-by-Step Secure Sharing
- Encrypt locally β Use a client-side tool to encrypt with AES-256-GCM
- Generate a strong key β 256-bit random key, never reused
- Set expiration β Configure auto-deletion after download or time limit
- Share the link securely β Send via encrypted messaging, not email
- Verify the recipient β Confirm they received the correct file hash
Password-Protected Archives
For simpler scenarios, a password-protected ZIP or 7z archive provides decent protection. Use AES-256 encryption (7-Zip's default), not the legacy ZipCrypto algorithm which has known vulnerabilities. Share the archive through one channel and the password through a different channel β never together.
Metadata Leaks to Watch For
Even encrypted files can leak information through metadata β file names, sizes, timestamps, and EXIF data in images. Strip metadata before sharing sensitive documents. The Peasy privacy tools can help you inspect and remove metadata from files entirely within your browser.