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to HTTP CONNECT but implemented over the OpenVPN protocol.
1. Client connects to relay server as if it were connecting
to an ordinary OpenVPN server.
2. Client authenticates to relay server using its client
certificate.
3. Client sends a PUSH_REQUEST method to relay server which
then replies with a RELAY message instead of PUSH_REPLY.
4. On receiving the RELAY message, the client attempts to
reconnect using the existing transport socket. The
server will proxy this new connection (at the transport
layer) to a second server (chosen by the relay server)
that is the target of proxy.
5. The client must establish and authenticate a new session
from scratch with the target server, only reusing the
transport layer socket from the original connection to
the relay server.
6. The relay acts as a man-in-the-middle only at the
transport layer (like most proxies), i.e. it forwards
the encrypted session between client and target server
without decrypting or having the capability to decrypt
the session.
7. The client is designed to protect against potentially
untrusted or malicious relays:
(a) The client never transmits the target server
username/password credentials to the relay server.
(b) The relay forwards the encrypted OpenVPN session
between client and target server without having
access to the session keys.
(c) The client configuration has a special directive
for relay server CA (<relay-extra-ca>) and relay
server tls-auth key (<relay-tls-auth>) to allow
for separation of TLS/crypto configuration between
relay and target servers.
(d) The client will reject any PUSH_REPLY messages
from the relay itself to prevent the relay from
trying to establish a tunnel directly with the
client.
Example configuring a client for relay:
# remote addresses point to the relay server
remote ... 1194 udp
remote ... 443 tcp
# include all other directives for connecting
# to the target server
# enable relay mode
relay-mode
# constrain the relay server's cert type
relay-ns-cert-type server
# include extra CAs that validate the relay
# server cert (optional).
<relay-extra-ca>
-----BEGIN CERTIFICATE-----
. . .
-----END CERTIFICATE-----
</relay-extra-ca>
# specify the TLS auth key for the relay server
relay-key-direction 1
<relay-tls-auth>
-----BEGIN OpenVPN Static key V1-----
. . .
-----END OpenVPN Static key V1-----
</relay-tls-auth>
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|---|---|---|
| .. | ||
| authcert.hpp | ||
| authcreds.hpp | ||
| cr.hpp | ||
| validatecreds.hpp | ||