Zero-App, Auto-Purge Document Printing for Public Cyber Cafés: Reducing Personal Data Leftovers on Shared Print Counters in India

Citizens across India print identity, education and financial documents at cyber cafés, Common Service Centres and photocopy shops. Files usually reach the shop computer through a messaging app or a USB drive, and copies stay behind on that shared computer long after the customer leaves. We describe PrintKrlo, a browser-based print workflow for such counters: the customer scans a QR code at the counter and uploads files from a mobile browser without installing an app or sharing a phone number; the shop computer opens the job in the browser's PDF viewer under a no-store caching policy, and the server deletes the temporary copy shortly after printing (or after 30 minutes if never printed). We define a threat model for shared print counters and compare the messaging-app workflow with PrintKrlo in a controlled test of 30 print jobs (20 messaging-app, 10 PrintKrlo) on one Windows shop computer, checking six storage locations for leftover copies, and time each job at the counter. With the messaging app's web client, a copy of the document remained in the Downloads folder, in browser storage and in Windows Recent items after every one of the 20 jobs; with PrintKrlo, no copy was found in any of the six locations after any of the 10 jobs, and browser network logs show every cache entry for the uploaded file being discarded without its body being written to disk. Median counter time was similar (27.4 s vs. 26.4 s), so the privacy gain did not cost time. We discuss what the design does not protect against, including printer spooling, server-side deletion limits and trust in the operator.