There was an external audit in 2021 – https://research.nccgroup.com/2021/10/27/public-report-whatsapp-end-to-end-encrypted-backups-security-assessment/#:~:text=

There was an external audit in 2021 – https://research.nccgroup.com/2021/10/27/public-report-whatsapp-end-to-end-encrypted-backups-security-assessment/#:~:text=Public%20Report%20%E2%80%93%20WhatsApp%20End%2Dto%2DEnd%20Encrypted%20Backups%20Security%20Assessment,-Jennifer%20Fernick%20Cryptography&text=During%20the%20summer%20of%202021,to%2DEnd%20Encrypted%20Backups%20project https://research.nccgroup.com/2021/10/27/public-report-whats....