Security and data handling

Charts and templates

A chart’s datasheet and options are stored in the deck with the chart’s shapes: as shape tags in PowerPoint, and as document properties in Google Slides. Nothing about them is sent to Deckcell’s server.

Excel links

• Each workbook gets a random write key (100 bits), kept in the workbook’s settings. It never leaves Excel.
• The workbook’s read code is derived from the key with SHA-256 and can’t be turned back into it. Linked ranges are filed under the read code.
• Decks store only the read code. Anyone with the deck can refresh its charts but can’t change the workbook’s numbers.
• Codes travel in request headers, not URLs, so they stay out of access logs.
• New code in the Excel pane replaces the key and revokes the old read code.
• The server has no endpoint that lists workbooks. Workbooks untouched for 180 days are deleted.
• Every record is validated on the way in and out; there are rate limits per client.

A read code is a bearer secret: anyone who has it can read that workbook’s linked ranges until it’s replaced.

Team library

• A team is a 20-character code; anyone with it can read, add and delete items. The server files each team under a SHA-256 hash of the code.
• Workbook links are removed from charts before they’re shared.
• Items are validated and capped in size; teams untouched for a year are deleted.

The add-in itself

• The server refuses requests from hosts other than its own, which blocks DNS-rebinding attacks, and sends no cross-origin headers, so other sites can’t call it.
• Deckcell has no user accounts, so there are no passwords to leak.

Questions about security? Email [email protected].