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How does the app figure out another telephone number has a WhatsApp account? How does it fetch profile information for that telephone number without communicati

by _wmd 11y ago

How does the app figure out another telephone number has a WhatsApp account? How does it fetch profile information for that telephone number without communicating the desire to fetch it to WhatsApp? Perhaps WhatsApp ships their entire profile photo and telephone number database to every phone

kccqzy 11y ago
There are two things here: a) the app can take a snapshot of your phone book, upload it, associate it with your own WhatsApp account, and then keep the remote version synchronised; and b) the app can periodically perform disparate requests to the central directory server to query the profile information for each number. As far as I know, WhatsApp uses approach b. These two may seem similar but in approach b, WhatsApp the service wouldn't learn of any contact removals. WhatsApp the app would, of course, but the service wouldn't. Now, with some simple filtering and statistics, WhatsApp the service can deduce your phone book with some certainty, but I believe most would agree that it is materially different from actually uploading your phone book.
- pfg 11y ago
  > Now, with some simple filtering and statistics, WhatsApp the service can deduce your phone book with some certainty, but I believe most would agree that it is materially different from actually uploading your phone book. No, not really. Both implementations give WhatsApp a complete list of all my contacts. The fact that one of those implementations might not be 100% accurate because of deleted contacts changes nothing - if you're someone who's worried about a third party having your contact list, it doesn't make sense to think "but hey, they don't know I removed $FOO last week, so their list isn't 100% accurate!". Both implementations mean you'll have to take their word on what they will and won't do with the data, so there's really not much of a practical difference.

by _wmd 11y ago

kccqzy 11y ago

There are two things here: a) the app can take a snapshot of your phone book, upload it, associate it with your own WhatsApp account, and then keep the remote version synchronised; and b) the app can periodically perform disparate requests to the central directory server to query the profile information for each number. As far as I know, WhatsApp uses approach b. These two may seem similar but in approach b, WhatsApp the service wouldn't learn of any contact removals. WhatsApp the app would, of course, but the service wouldn't. Now, with some simple filtering and statistics, WhatsApp the service can deduce your phone book with some certainty, but I believe most would agree that it is materially different from actually uploading your phone book.

pfg 11y ago
> Now, with some simple filtering and statistics, WhatsApp the service can deduce your phone book with some certainty, but I believe most would agree that it is materially different from actually uploading your phone book. No, not really. Both implementations give WhatsApp a complete list of all my contacts. The fact that one of those implementations might not be 100% accurate because of deleted contacts changes nothing - if you're someone who's worried about a third party having your contact list, it doesn't make sense to think "but hey, they don't know I removed $FOO last week, so their list isn't 100% accurate!". Both implementations mean you'll have to take their word on what they will and won't do with the data, so there's really not much of a practical difference.