cyphertite uses a private (per-user) deduplication pool, not a global deduplication pool like dropbox and many other online storage providers.
Example 1 - user1 uploads file1, then at a later time user1 tries to upload file1 again. the 2nd occurrence of the data in file1 is recognized as a duplicate of what has already been stored, so the service does not re-upload the bulk data of file1. this saves bandwidth, time, cpu cycles etc.
Example 2 - user1 uploads file1, then at a later time user2 uploads file1. in a private (per-user) deduplication pool, both user1 and user2 would need to separately upload a copy of file1, but in a global deduplication pool, user2 would not need to actually upload the bulk file data since it can reference data that user1 uploaded earlier.
the upshot here is that each user has their own separate crypto keys that are used client-side, similar to spideroak, tarsnap, etc.
i could get into the details here, but it's pretty well summarized in our infographic and crypto whitepaper
Example 1 - user1 uploads file1, then at a later time user1 tries to upload file1 again. the 2nd occurrence of the data in file1 is recognized as a duplicate of what has already been stored, so the service does not re-upload the bulk data of file1. this saves bandwidth, time, cpu cycles etc.
Example 2 - user1 uploads file1, then at a later time user2 uploads file1. in a private (per-user) deduplication pool, both user1 and user2 would need to separately upload a copy of file1, but in a global deduplication pool, user2 would not need to actually upload the bulk file data since it can reference data that user1 uploaded earlier.
the upshot here is that each user has their own separate crypto keys that are used client-side, similar to spideroak, tarsnap, etc.
i could get into the details here, but it's pretty well summarized in our infographic and crypto whitepaper
https://www.cyphertite.com/papers/CT_InfoGraphic.pdf https://www.cyphertite.com/papers/WP_Crypto.pdf