How would you secure a moderated screen-sharing session end to end?

WHAT THIS TESTS: This question probes whether you can design a privacy-first architecture for highly sensitive streaming data. The interviewer cares about your ability to reason across the entire lifecycle, real-time transport, ephemeral processing, durable storage, and governance, rather than reciting a single encryption standard.

A GOOD ANSWER COVERS: A strong response walks through five layers in order. First, transport security for the video stream. You should mention WebRTC with DTLS-SRTP for hop-by-hop encryption or ideally end-to-end encryption using Insertable Streams so that the SFU cannot decrypt media. Second, session and identity controls. This means short-lived JWT tokens, unique room IDs, moderator authentication, and waiting-room patterns to prevent unauthorized joins. Third, artifact security at rest. Recordings must be encrypted with AES-256 using keys held in a separate KMS, uploaded over TLS, chunked to survive network drops, and hashed for integrity. Fourth, infrastructure hardening. Disable persistent chat logs, ensure video frames never hit application logs, auto-purge memory buffers, and restrict researcher machines with MDM policies that block local screen recorders. Fifth, governance and consent. Capture explicit consent before stream start, apply automated retention policies, run transcripts through PII redaction pipelines, watermark playback with viewer identity, and maintain audit logs for every access event.

COMMON WRONG ANSWERS: Red flags include claiming TLS alone is sufficient for video content, storing encryption keys in the same object storage bucket as recordings, or ignoring that screen shares often expose third-party credentials and private messages. Another major miss is failing to secure the moderator endpoint, such as allowing downloads or screenshots on the researcher device. Proposing email distribution of session links without expiration or role-based access is also a significant gap.

LIKELY FOLLOW-UPS: Expect the interviewer to ask how you would handle a participant accidentally exposing passwords during a screen share, what your key rotation strategy is for archived sessions, or how you would execute a GDPR deletion request when immutable backups exist. They may also ask you to compare the threat model of a compromised vendor versus a compromised moderator laptop.

ONE CONCRETE EXAMPLE: Imagine a participant briefly shares their email inbox containing patient data. The architecture should enforce E2EE so the SFU sees only ciphertext, write the recording to an encrypted S3 bucket in a dedicated account with no cross-region replication, process the transcript through an automated PII scanner before indexing, stream playback through a browser-based player that disables right-click downloads while burning the researcher email address into the video as a watermark, and auto-delete the file after ninety days with a cryptographic erasure of the decryption key.