DontTell

DontTell is a product concept for sharing sensitive content without making the server the primary trust boundary. The core constraint: the server should never hold plaintext.

Problem

Most sharing tools — even “secure” ones — encrypt in transit but store decryptable content server-side. The service has the key. Compliance with law enforcement requests, data breaches, or insider access can expose user content regardless of the TLS layer.

DontTell inverts this: encryption happens in the browser before any network request. The server stores ciphertext it cannot decrypt.

Architecture constraints

Encryption layer:

• Content is encrypted with XChaCha20-Poly1305 before leaving the browser
• The encryption key is derived client-side using Argon2id from a user-supplied passphrase or generated randomly
• The key never travels to the server — it lives only in the URL fragment (#key=...) or is shared out-of-band

Access model:

• Shares have configurable TTL — the server deletes ciphertext after expiry
• Optional: single-use links that invalidate after first download
• Optional: passphrase gate at the server layer as a second factor (the server still cannot read the content)

Server role:

• Store opaque ciphertext blobs
• Enforce TTL and use-count limits
• Serve the static client application
• No user accounts, no logging of content metadata beyond necessary operational data

What the server knows

• That a share was created (timestamp, approximate size)
• When it was accessed (timestamp, IP if logged)
• Nothing about the content

This is the minimal trust surface for a sharing tool.

Tradeoffs

Fragment-based key sharing means the key is not sent to the server (fragments are client-only) but is visible in browser history, bookmarks, and server logs if the user pastes the full URL. Users must understand this boundary.

Argon2id key derivation adds brute-force resistance but requires meaningful passphrases. Short passphrases are recoverable offline against the ciphertext.

No server-side key escrow means lost keys mean lost content — intentionally. Recovery is the user’s responsibility.

Status

Concept stage. The cryptographic primitives are available natively in modern browsers via the Web Crypto API. The architecture is implementable; the product work is in the UX and trust communication, not the cryptography.