Pascal Junod
@cryptopathe.me
applied cryptographer - certified nerd god - head of cryptography & research at duokey - founder modulo p - ex-Snap - co-founder ex-strong.codes - has-been professor - trail runner - aidjolat
FTR, how contact discovery works has been discussed in the following blog posts: signal.org/blog/contact... (2014), signal.org/blog/private... (2017) and signal.org/blog/buildin... (2022). 3/3
The Difficulty Of Private Contact Discovery
Building a social network is not easy. Social networks have value proportional to their size, so participants aren’t motivated to join new social networks which aren’t already large. It’s a paradox wh...
signal.org
October 30, 2025 at 7:24 AM
FTR, how contact discovery works has been discussed in the following blog posts: signal.org/blog/contact... (2014), signal.org/blog/private... (2017) and signal.org/blog/buildin... (2022). 3/3
So, clients disclose their full address book to the enclave: compromised SGX enclaves would not just leak the resulting social (sub-)graph, but also private information (e.g., phone numbers, name, ...) of non-Signal users. 2/3
October 30, 2025 at 7:24 AM
So, clients disclose their full address book to the enclave: compromised SGX enclaves would not just leak the resulting social (sub-)graph, but also private information (e.g., phone numbers, name, ...) of non-Signal users. 2/3
AFAIU, contact discovery works as follows: clients sends their address book identifiers in a secure way to the SGX enclave, that computes the intersection with the set of all Signal registered users and sends it back (securely) to the client. 1/3
October 30, 2025 at 7:24 AM
AFAIU, contact discovery works as follows: clients sends their address book identifiers in a secure way to the SGX enclave, that computes the intersection with the set of all Signal registered users and sends it back (securely) to the client. 1/3
Then: will Signal stop running contact discovery if it is not possible to implement it securely? Other secure messengers (e.g. @olvid.io) do this by design. This is a security vs. UX/growth tradeoff.
October 29, 2025 at 4:26 PM
Then: will Signal stop running contact discovery if it is not possible to implement it securely? Other secure messengers (e.g. @olvid.io) do this by design. This is a security vs. UX/growth tradeoff.
They do rely on Intel SGX for hardening their contact discovery protocol. The next question is: how likely is a physical attack on AWS HW?
October 29, 2025 at 3:16 PM
They do rely on Intel SGX for hardening their contact discovery protocol. The next question is: how likely is a physical attack on AWS HW?
Ouch, certain dogs are really a nightmare for runners. Take care!
October 29, 2025 at 3:04 PM
Ouch, certain dogs are really a nightmare for runners. Take care!