I wonder how the client manages contacts. In "Know your contacts" article is written:
"Although it is very unlikely, if you notice someone's avatar change, their account may have been compromised. Peerio will notify you if this happens, and it is advised to communicate with your contact outside of Peerio to confirm that you both are seeing the same avatar."
How would the client recognise the change? Does it just download plaintext contact database from server and compare it with its offline cache, or is the database encrypted for its user, transmitted between the client and the server in this form, and therefore inalterable for a possible attacker on the server (or is it just unencrypted, but signed)?
According to "Peerio's policy" the server actually stores the plaintext contact lists (and it's probably necessary to handle files sharing and contact discovery), but I'd like to know, how the client checks integrity and validity of it's locally created database (especially after login from a different installation) and therefore protects the user from MITM attacks without need of remembering all his/her contacts' fingerprints.
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