[1]https://www.engadget.com/facebook-analyze-encrypted-messages-ad-targeting-175
739715.html?bcmt=1

   [2][INS: Facebook :INS]  is reportedly looking into analyzing the
   content of encrypted data without having to decrypt it. The company is
   recruiting artificial intelligence researchers to study the matter,
   according to [3]The Information. Their research could pave the way for
   Facebook to target ads based on encrypted WhatsApp messages. Facebook
   could also use the findings to encrypt user data without affecting its
   ad targeting approaches.

   This area of research is called "homomorphic encryption," which relies
   heavily on mathematics. Microsoft, Amazon and Google are also working
   on the approach. The aim of homomorphic encryption is to allow
   companies to read and analyze data while keeping it encrypted to
   protect information from cybersecurity dangers and to maintain privacy.

References

   1. https://www.engadget.com/facebook-analyze-encrypted-messages-ad-targeting-175739715.html?bcmt=1
   2. https://www.engadget.com/tag/facebook
   3. https://www.theinformation.com/articles/facebook-researchers-hope-to-bring-together-two-foes-encryption-and-ads