end to end encrypted chat with LDAP authentication

authentication using Apache Directory Studio (LDAP)
client generates private key and certificate signing request
the CA (server.py) stores a signed certificate for that user
when a client wants to send a message to another destination:
1. first it requests the destinations certificate from the server
2. then it encrypts the message using its public key and sends it to the server
when a client receives an encrypted message:
1. it decrypts it using its private key

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