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# gemini-demo-1
# gemini-certificate-validation-demo-1
Minimal but usable interactive Gemini client in < 100 LOC of Python 3
This is a minimal Gemini client capable of (self-signed) certificate
validation using the additional network perspective of a Tor exit node.
When the client encounters a new certificate for a host, it makes a TLS
connection to the same host via Tor, in order to obtain its certificate
from a second vantage point. The user is notified on certificate
mismatch or connection failure.
## Rationale
This method should detect any local man-in-the-middle attack
(originating from the same LAN, for instance) and should also provide
protection over a more or less broad area of the Internet, depending on
the exit node's position in the network graph and its DNS resolution
setup. Any attack will trigger an alert unless it affects both the user
and the exit node (whether it's a BGP hijack, a DNS compromise or
whatever else).
One of the original design criteria for the Gemini protocol was that
"a basic but usable (not ultra-spartan) client should fit comfortably
within 50 or so lines of code in a modern high-level language.
Certainly not more than 100". This client was written to gauge how
close to (or far from!) that goal the initial rough specification is.
This validation method works best when the exit node is far from the
user's position. Users may configure Tor to select specific exit nodes
by setting
the [ExitNodes](https://2019.www.torproject.org/docs/tor-manual.html.en#ExitNodes)
and [StrictNodes](https://2019.www.torproject.org/docs/tor-manual.html.en#StrictNodes)
options in their `torrc` file. The `ExitNodes` option accepts
countries, IP address ranges and node fingerprints. For example, this
is how to only select exits located in France:
## Capabilities
```
ExitNodes {fr}
StrictNodes 1
```
This crude but functional client:
False alarms can be triggered by MITM attacks on the exit node's end.
And, obviously, validation does not work for servers which block Tor.
* Has a minimal interactive interface for "Gemini maps"
* Will print plain text in any encoding if it is properly declared in
the server's response header
* Will handle binary files using programs specified in `/etc/mailcap`
(so you can, e.g. view images)
* Will follow redirects
* Will report errors
* Does NOT DO ANY validation of TLS certificates
Validated certificates are kept in memory for the duration of the
browsing session. Tor is assumed to be listening on localhost, port
9050.
It's a *snug* fit in 100 lines, but it's possible. A 50 LOC client
would need to be much simpler.
## Usage
Run the script and you'll get a prompt. Type a Gemini URL (the scheme
is implied, so simply entering e.g. `gemini.conman.org` will work) to
visit a Gemini location.
If a Gemini menu is visited, you'll see numeric indices for links, ala
VF-1 or AV-98. Type a number to visit that link.
There is very crude history: you can type `b` to go "back".
Type `q` to quit.
This is a fork of Solderpunk's [minimal Gemini
client](https://tildegit.org/solderpunk/gemini-demo-1) written in
Python.