Transport encryption and client-side encryption solve different problems
HTTPS is essential. It protects data from many network observers while it moves between browser and server. But the server normally terminates HTTPS and receives the plaintext that the browser sent.
With client-side encryption, the browser transforms the file into ciphertext first. HTTPS then transports ciphertext. The server can store and return those bytes without holding the decryption key used by a standard link.
Integrity matters as much as secrecy
Encryption should detect modification. AES-GCM is an authenticated-encryption mode: decryption fails if protected bytes or associated metadata change. For segmented large files, each segment needs a unique nonce and its position must be cryptographically bound so parts cannot be reordered or substituted unnoticed.
File names and content types can also reveal sensitive context. A privacy-focused design encrypts or authenticates metadata rather than leaving it as ordinary object-store labels.
Large files require careful streaming
Loading a gigabyte into memory can crash a browser or expose more plaintext than necessary. Segmenting allows bounded-memory encryption, retryable upload, and ordered decryption. Resume state should be short-lived, confined to the user's browser, and tied to the same local file.
Storage uploads should use narrow, expiring signed URLs. Completing an upload must verify the intended object set and size before publishing a retrievable Relay.
Understand the deletion timeline
For small text payloads, atomic deletion during retrieval can be immediate. Files need a slightly different sequence: consume the active Relay, issue time-limited access to the already encrypted object, then delete the storage object after the download and retry window.
A trustworthy description names both events. 'Unavailable for another retrieval' can be immediate while physical encrypted-object cleanup follows shortly afterward. Expired and abandoned uploads also need an authenticated cleanup queue and monitoring.
Questions to ask a file-sharing provider
Evaluate the complete lifecycle, not only the encryption badge:
- Where does encryption occur, and can the provider receive the key?
- Are file names, sizes, and content types protected or minimized?
- Does authenticated encryption verify tampering and segment order?
- How are upload URLs scoped and expired?
- When is the active link consumed, and when are encrypted objects deleted?
- What metadata and logs remain after deletion?