In April, WhatsApp announced the launch of a new cryptographic security feature to automatically verify a secured connection based on key transparency. Key transparency helps strengthen the guarantee that end-to-end encryption provides to private, personal messaging applications in a transparent manner available to all. Rolling out a feature like this to WhatsApp's user base is not a small feat and requires some clever engineering to scale to the billions of users relying on WhatsApp to stay in touch with friends, family and business. Pascal is joined by Sean and Kevin to discuss what Key Transparency means in practice and the various challenges they encountered as they scaled it up to billions of users. Got feedback? Send it to us on Threads (https://threads.net/@metatechpod), Twitter (https://twitter.com/metatechpod), Instagram (https://instagram.com/metatechpod) and don’t forget to follow our host @passy (https://twitter.com/passy, https://mastodon.social/@passy, and https://threads.net/@passy_). Fancy working with us? Check out https://www.metacareers.com/. Links Infer: https://fbinfer.com/ Infer on GitHub: https://github.com/facebook/infer MTP Episode 18 about Infer: https://pca.st/5U9V Deploying key transparency at WhatsApp - Engineering at Meta: https://engineering.fb.com/2023/04/13/security/whatsapp-key-transparency/ GitHub - facebook/akd: An implementation of an auditable key directory: https://github.com/facebook/akd/  Parakeet: Practical Key Transparency for End-to-End Encrypted Messaging: https://www.ndss-symposium.org/ndss-paper/parakeet-practical-key-transparency-for-end-to-end-encrypted-messaging/  SEEMless: Secure End-to-End Encrypted Messaging with less trust: https://eprint.iacr.org/2018/607 Coniks: Bringing Key Transparency to End Users: https://www.usenix.org/conference/usenixsecurity15/technical-sessions/presentation/melara  IETF Working Group on Key Transparency: https://datatracker.ietf.org/wg/keytrans/about   Timestamps Intro 0:06 News Update: Infer turns 10 1:34 Interview Intro 4:27 Intro Kevin 4:45 Intro Sean 6:07 WhatsApp's mission 6:47 PETs 7:58 E2E basics 8:59 Key transparency 10:32 Crypto community response 18:20 End-user changes 19:57 Technical challenges and zero-knowledge proofs 23:18 AKD 28:27 Internal deployment 32:02 Outro 42:16 Bloopers 43:05