Security consideration

[yuanqili]

Goal: Messages are encrypted and then transmitted through the server (stored in server's database), but the server doesn't know anything about the message. It just passes the message to the target client.

Idea: Using public/private key pair.

Detail:

• PA, VA: public and private key of Alice, PB, VB: public and private key of Bob.
• Server will store all users' public keys.
• For a message msg, Alice sends PA(msg) and PB(msg), i.e., the message encrypted using Alice's public key and Bob's public key.
• Server will sends PB(msg) to Bob. Bob is able to view the message by VB(PB(msg)) using his private key.
• If Alice wants to view her message history, she can acquire PA(msg) from the server, and decrypt using her private key VA.

[yuanqili]

Instead of sending PA(msg) and PB(msg) to server, only send VA(msg). The server will automatically encrypts it again using PA. It also makes Bob able to verify Alice's signature.

[yuanqili]

See PKI

[yuanqili]

Probably using SSL connects to the server (and buy a cert)