I've always been a little worried about people who post e.g. a Calendly link that shows their full availability and lets you set an appointment. Do you really want to reveal how not-busy you are? Well, apparently the NIST is now warning that it's also a big security risk, and advises a few protocols to obfuscate your true availability. I got my hands on an early draft of the proposal.
🛡️ NIST IR 8429-DRAFT
Presence Obfuscation in Federated Scheduling Systems
Guidelines for Temporal Metadata Minimization in Collaborative Availability Platforms
1. Scope and Purpose
Modern calendaring tools often expose excessive availability to collaborators, contractors, and external partners. These systems—by default—permit observers to view large blocks of unscheduled time, often across multiple days, weeks, or recurring patterns.
While intended to facilitate meeting scheduling, such broad exposure of free/busy data introduces serious risks:
- Temporal profiling
- Passive inferences about workload or engagement
- Social graph deduction via availability overlap
- Identification of predictable solitude windows
These exposures disproportionately impact individuals with high meeting asymmetry—those who receive more requests than they initiate—and those whose roles rely on maintaining controlled perceptions of demand.
2. Problem Definition
The visibility of extensive availability windows has emerged as a key metadata leakage vector in both organizational and interpersonal contexts. Specifically:
- Open calendars reveal a subject’s unstructured time density, which may be misinterpreted as low workload or underutilization.
- Observers may make inferences about social graph positioning based on recurring exclusion from scheduled events.
- In adversarial contexts, such patterns can even aid in physical vulnerability modeling, including mapping of long-duration solitude intervals.
Note: While this report avoids normative language regarding “perceived busyness,” we recognize it as a functional privacy parameter in professional ecosystems.
3. Mitigation Strategy: Presence Obfuscation Layer (POL-1)
POL-1 is a modular framework for introducing structured ambiguity into exposed calendrical availability, ensuring that observed scheduling surfaces retain semantic plausibility without revealing raw temporal capacity.
It is not a deception system, but rather a context-aware redaction buffer for collaborative environments.
4. System Components
4.1 Observer-Coherent Subset Exposure (OCEP)
Availability is partitioned by observer class (e.g., internal peer, external client, HR metadata node) to ensure deterministic, plausible views that are not cross-correlatable. No single observer can reconstruct the true surface.
4.2 Continuity Entropy Injection (CEI)
Injects plausible placeholder constraints and pseudo-events to avoid the appearance of long unbroken availability, particularly during mid-day periods known to trigger unsolicited booking attempts.
4.3 Foreground Availability Perturbation System (FAPS)
Applies low-amplitude randomization at event boundaries to disrupt timing-based inference attacks. Designed to deflect automated meeting tools and high-frequency schedulers without impeding intentional collaboration.
Note: FAPS may be disabled in constrained or high-determinism scheduling environments (e.g., surgical coordination, launch windows).
4.4 Behavioral Availability Normalization Kernel (BANK)
Aligns exposed availability with industry-standard load models, e.g., “Product Manager (Mid-Level, West Coast)” or “Postdoctoral Researcher (Remote EU).” Useful for avoiding apparent availability outliers that may bias request behavior.
4.5 Fail-Safe Redaction Coherence Module (FRCM)
Final pass verifier that ensures no exposed schedule appears suspiciously empty, implausibly overbooked, or temporally inconsistent with the subject’s graph classification.
5. Application Scenarios
| Scenario | Exposure Risk | Mitigation Stack |
|---|---|---|
| Early-career engineer in open scheduling org | Appears to have 4–5 open hours/day | BANK + CEI + OCEP |
| Public figure with assistants booking on their behalf | High-profile scheduling scrape risk | FAPS + FRCM |
| Remote worker in non-managerial role | Pattern of availability invites frequent “quick chats” | OCEP + CEI |
6. Deployment and Compliance
POL-1 is suitable for deployment across major federated scheduling platforms (CalDAV, Exchange, Google Calendar API v3). Compatibility modules are provided for Outlook Graph Surfaces and GSuite Legacy Redirection endpoints.
Note: Organizations governed by EO 14217 (“Minimum Obfuscation Baselines for Federal Metadata Systems”) must deploy POL-1 or equivalent by Q3 FY25.
7. Availability
A reference implementation of POL-1 is available on the NIST GitHub mirror under a modified FIPS-aware BSD license:
📎 https://github.com/nist-opsec/pol1
"Availability is a feature. Apparent availability is a liability."
— NIST IR 8429-DRAFT, April 1, 2025
