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Version 13 (modified by Antoine Martin, 4 months ago) (diff)

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SSL Encryption


Introduction

New in version 1.0, for more details see #1252.

This option can more easily go through some firewalls and may be required by some network policies. Client certificates can also be used for authentication.

There are a lot more options to configure and certificates to deal with. See https://docs.python.org/2/library/ssl.html, on which this is based.

It is only applicable to TCP sockets, not unix domain sockets. Do not assume that you can just enable SSL to make your connection secure.

Example

  • use an existing certificate "cert.pem" (see below for creating one)
  • start a server with TCP and SSL support:
    xpra start --start=xterm \
        --bind-tcp=0.0.0.0:10000 --ssl-cert=/path/to/cert.pem --ssl=on
    

or for SSL only:

xpra start --start=xterm \
    --bind-ssl=0.0.0.0:10000 --ssl-cert=/path/to/cert.pem
  • client:
    xpra attach ssl:127.0.0.1:10001
    

SSL Mode

The TCP to SSL socket upgrade can be used with SSL clients, websockets clients (html5 clients) or HTTPS connections. Unfortunately, not all of them at the same time. (see ticket:1213#comment:5 for details - #1504 may eventually lift this limitation)

The option ssl=MODE can be used to select which clients protocols will be allowed on the bind-tcp sockets:

Mode Client Protocol
SSL Websockets Secure Websockets
auto
(default)
Yes Yes No
TCP Yes No No
www No Yes Yes

Using a self signed certificate

Generate a certificate:

openssl req -new -x509 -days 365 -nodes -out self.pem -keyout self.pem -sha256

To avoid this error when the client connects:

[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)

temporarily add --ssl-server-verify-mode=none to your client command line

Securing SSL with self signed CA and certificates

See The Most Dangerous Code in the World: Validating SSL Certificates in Non-Browser Software and Beware of Unverified TLS Certificates in PHP & Python. See also: Fallout from the Python certificate verification change.

Since the server certificate will not be signed by any recognized certificate authorities, you will need to send the verification data to the client via some other means... This will no be handled by xpra, it simply cannot be. (same as the AES key, at which point... you might as well use AES)


# generate your CA key and certificate:
openssl genrsa -out ca.key 4096
# (provide the 'Common Name', ie: 'Example Internal CA')
openssl req -new -x509 -days 365 -key ca.key -out ca.crt
# generate your server key:
openssl genrsa -out server.key 4096
# make a signing request from the server key:
# (you must provide the 'Common Name' here, ie: 'localhost' or 'test.internal')
openssl req -new -key server.key -out server.csr
# sign it with your CA key:
openssl x509 -req -days 365 \
    -in server.csr -out server.crt \
    -CA ca.crt -CAkey ca.key \
    -CAserial ./caserial -CAcreateserial
# verify it (it should print "OK"):
openssl verify -CAfile ca.crt ./server.crt

You can now start your xpra server using this key:

xpra start --start=xterm \
    --bind-tcp=0.0.0.0:10000 --ssl=on --ssl-cert=`pwd`/server.crt --ssl-key=`pwd`/server.key

Use openssl to verify that this xpra server uses SSL and that the certificate can be verified using the "ca.crt" authority file: (it should print Verify return code: 0 (ok)):

openssl s_client -connect 127.0.0.1:10000  -CAfile /path/to/ca.crt < /dev/null

Connect the xpra client:

xpra attach ssl:localhost:10000 --ssl-ca-cert=/path/to/ca.crt

Sending the CA data

In some cases, it may be desirable to supply the CA certificate on the command line or in a session file. Here's how.

Convert a CA file to hex:

python -c "import sys,binascii;print binascii.hexlify(open(sys.argv[1]).read())" ca.crt

Convert hex back to data to verify (only part of the data shown here):

python -c "import sys,binascii;print binascii.unhexlify(sys.argv[1])" \
    2d2d2d2d2d424547494e2043455254494649434154452d2d2d2d2d0a4d4949

Use it directly in the xpra command:

xpra attach ssl:localhost:10000 \
    --ssl-ca-data=2d2d2d2d2d424547494e...4452d2d2d2d2d0a

Alternatively, place all of these in a connection file you can just double click on:

echo > ssl-test.xpra <<EOF
host=localhost
autoconnect=true
port=10000
mode=ssl
ssl-ca-data=2d2d2d2d2d424547494e...4452d2d2d2d2d0a
EOF