WhatsApp contact uplod mechanism continues here [1].
It means, that if the contact list contains numbers which have not accepted WhatsApp ToS, their content is stored only as hash.
When the user starts using WhatsApp, their number and hash is being mapped.
Vaguely described as
> Each cryptographic hash value is stored on WhatsApp’s servers, linked to the WhatsApp users who uploaded the corresponding phone numbers before they were hashed so that we can more efficiently connect you with these contacts when they join WhatsApp.
Which means that WhatsApp knows the numbers of the WhatsApp users, and how they interact together.
Signal does not know numbers or how these contatcs interact.
It is described here [2]. Number is only needed for creating the unique hash.
Server knows only the recipient, not the sender.
> Signal does not know numbers or how these contatcs interact.
> It is described here [2]. Number is only needed for creating the unique hash. Server knows only the recipient, not the sender.
Signal does know everyone's numbers as everybody is logged into a Signal account on the server end (this is how your client fetches messages for your number). That same account and IP are also used when you send a message.
It means, that if the contact list contains numbers which have not accepted WhatsApp ToS, their content is stored only as hash. When the user starts using WhatsApp, their number and hash is being mapped.
Vaguely described as
> Each cryptographic hash value is stored on WhatsApp’s servers, linked to the WhatsApp users who uploaded the corresponding phone numbers before they were hashed so that we can more efficiently connect you with these contacts when they join WhatsApp.
Which means that WhatsApp knows the numbers of the WhatsApp users, and how they interact together.
Signal does not know numbers or how these contatcs interact.
It is described here [2]. Number is only needed for creating the unique hash. Server knows only the recipient, not the sender.
[1]: https://faq.whatsapp.com/423109552047857/?locale=en_US&refsr...
[2]: https://signal.org/blog/sealed-sender/