iMessage broke new ground in 2011 as the first widely available messaging service to provide secure end-to-end encryption by default. Ever since, we’ve been making ongoing improvements to iMessage security to protect our users’ most sensitive communications. This brief technical overview introduces the security model behind iMessage Contact Key Verification, a new feature available in the developer previews of iOS 17.2, macOS 14.2, and watchOS 10.2, that advances the state of the art of key directory security in messaging systems and allows users to verify they’re messaging only with the people they intend.