crypto: Implement TLS Pre-Shared Keys (PSK).

Pre-Shared Keys (PSK) is a simpler mechanism for enabling TLS
connections than using certificates.  It requires only a simple secret
key:

  $ mkdir -m 0700 /tmp/keys
  $ psktool -u rjones -p /tmp/keys/keys.psk
  $ cat /tmp/keys/keys.psk
  rjones:d543770c15ad93d76443fb56f501a31969235f47e999720ae8d2336f6a13fcbc

The key can be secretly shared between clients and servers.  Clients
must specify the directory containing the "keys.psk" file and a
username (defaults to "qemu").  Servers must specify only the
directory.

Example NBD client:

  $ qemu-img info \
    --object tls-creds-psk,id=tls0,dir=/tmp/keys,username=rjones,endpoint=client \
    --image-opts \
    file.driver=nbd,file.host=localhost,file.port=10809,file.tls-creds=tls0,file.export=/

Example NBD server using qemu-nbd:

  $ qemu-nbd -t -x / \
    --object tls-creds-psk,id=tls0,endpoint=server,dir=/tmp/keys \
    --tls-creds tls0 \
    image.qcow2

Example NBD server using nbdkit:

  $ nbdkit -n -e / -fv \
    --tls=on --tls-psk=/tmp/keys/keys.psk \
    file file=disk.img

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/qemu-options.hx b/qemu-options.hx
index 81b1e99d58..16208f63f2 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4123,6 +4123,30 @@ expensive operation that consumes random pool entropy, so it is
 recommended that a persistent set of parameters be generated
 upfront and saved.
 
+@item -object tls-creds-psk,id=@var{id},endpoint=@var{endpoint},dir=@var{/path/to/keys/dir}[,username=@var{username}]
+
+Creates a TLS Pre-Shared Keys (PSK) credentials object, which can be used to provide
+TLS support on network backends. The @option{id} parameter is a unique
+ID which network backends will use to access the credentials. The
+@option{endpoint} is either @option{server} or @option{client} depending
+on whether the QEMU network backend that uses the credentials will be
+acting as a client or as a server. For clients only, @option{username}
+is the username which will be sent to the server.  If omitted
+it defaults to ``qemu''.
+
+The @var{dir} parameter tells QEMU where to find the keys file.
+It is called ``@var{dir}/keys.psk'' and contains ``username:key''
+pairs.  This file can most easily be created using the GnuTLS
+@code{psktool} program.
+
+For server endpoints, @var{dir} may also contain a file
+@var{dh-params.pem} providing diffie-hellman parameters to use
+for the TLS server. If the file is missing, QEMU will generate
+a set of DH parameters at startup. This is a computationally
+expensive operation that consumes random pool entropy, so it is
+recommended that a persistent set of parameters be generated
+up front and saved.
+
 @item -object tls-creds-x509,id=@var{id},endpoint=@var{endpoint},dir=@var{/path/to/cred/dir},priority=@var{priority},verify-peer=@var{on|off},passwordid=@var{id}
 
 Creates a TLS anonymous credentials object, which can be used to provide