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@ -322,7 +322,7 @@ Further considered solutions are explored in
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https://signal.org/blog/contact-discovery/. Signal's eventual solution of
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https://signal.org/blog/contact-discovery/. Signal's eventual solution of
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using Software Guard Extensions (detailed in
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using Software Guard Extensions (detailed in
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https://signal.org/blog/private-contact-discovery/) is considered impractical
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https://signal.org/blog/private-contact-discovery/) is considered impractical
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for a federated network, as it requires specialized hardware.
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for a federated network, as it requires specialised hardware.
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k-anonymity was considered as an alternative approach, in which the identity
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k-anonymity was considered as an alternative approach, in which the identity
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server would never receive a full hash of a 3PID that it did not already know
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server would never receive a full hash of a 3PID that it did not already know
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@ -410,10 +410,12 @@ Thus the conclusion is that while k-anon is harder to attack, it's unclear
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that this is actually enough of an obstacle to meaningfully stop a malicious
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that this is actually enough of an obstacle to meaningfully stop a malicious
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IS. Therefore we should KISS and go for a simple hash lookup with a rotating
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IS. Therefore we should KISS and go for a simple hash lookup with a rotating
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pepper (which is not much harder than a static pepper, especially if our
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pepper (which is not much harder than a static pepper, especially if our
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initial implementation doesn't bother rotating the pepper). Rather than trying
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initial implementation doesn't bother rotating the pepper). Rather than
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to make the k-anon approach work, we'd be better off spending that time
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trying to make the k-anon approach work, we'd be better off spending that
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figuring out how to store 3pids as hashes in the DB (and in 3pid bindings
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time figuring out how to store 3pids as hashes in the DB (and in 3pid
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etc), or how to decentralise ISes in general.
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bindings etc), or how to decentralise ISes in general. It's also worth noting
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that a malicious server may fail to rotate the pepper, making the rotation
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logic of questionable benefit.
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A radical model was also considered where the first portion of the
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A radical model was also considered where the first portion of the
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k-anonyminity scheme was done with an identity server, and the second would
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k-anonyminity scheme was done with an identity server, and the second would
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