Prekey Pogo: Investigating Security and Privacy Issues in WhatsApp's Handshake Mechanism
summary
Demonstrates a targeted prekey depletion attack that uses a small command-line client to repeatedly request one-time prekeys (WhatsApp stores ~800 per device and refills when fewer than 10 remain), and an asynchronous prekey clogging variant that triggers 503s and a denial-of-service. Shows platform differences: some Android models (e.g., Samsung) refill immediately while iPhones batch refills every ~10–15 minutes, enabling a PFS downgrade to the monthly signed-prekey window; also leaks device OS via key-ID initialization. Reported to Meta March 2025.
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chapters (9)
- 0:00Prekey Pogo study
- 1:37Testing methodology
- 2:41Encryption and multi-device
- 5:52Privacy leak in device enumeration
- 9:48Prekey depletion attack
- 13:47Prekey clogging DoS
- 15:55Meta's response
- 16:17Proposed mitigations
- 17:02Conclusions
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