An example secret is supplied in the ipsec.secrets file by default. You should change it by creating your own. With automatic keying you may have a shared secret up to 256 bits, which is then used during the key exchanges to make sure a man in the middle attack does not occur. To create a new shared secret, use the following commands:

[root@deep] /# ipsec ranbits 256  > temp

New, random keys are created with the ranbits(8) utility in the file named temp. The ranbits utility may pause for a few seconds if not enough entropy is available immediately.

Now that our new shared secret key has been created in the temp file, we must put it in the /etc/ipsec.secrets file. When editing the ipsec.secrets file, you should see something like the following appearing in your text editor. Each line has the IP addresses of the two gateways plus the secret. It should look something like this:

# This file holds shared secrets which are currently the only inter-Pluto
# authentication mechanism.  See ipsec_pluto(8) manpage.  Each secret is
# (oversimplifying slightly) for one pair of negotiating hosts.

# The shared secrets are arbitrary character strings and should be both
# long and hard to guess.

# Note that all secrets must now be enclosed in quotes, even if they have
# no white space inside them.

10.0.0.1 11.0.0.1         "jxVS1kVUTTulkVRRTnTujSm444jRuU1mlkklku2nkW3nnVu
V2WjjRRnulmlkmU1Run5VSnnRT"

1. Edit the ipsec.secrets file, vi /etc/ipsec.secrets and change the default secrets keys:

   10.0.0.1 11.0.0.1  " jxVS1kVUTTulkVRRTnTujSm444jRuU1mlkklku2nkW3nnVu
   V2WjjRRnulmlkmU1Run5VSnnRT "
   

   To read:

   208.164.186.1 208.164.186.2 "0x9748cc31_2e99194f_d230589b_cd846b57_dc070b01_74b66f34_19c40a1a_804906ed"
   

   Where 208.164.186.1 and 208.164.186.2 are the IP addresses of the two gateways and "0x9748cc31_2e99194f_d230589b_cd846b57_dc070b01_74b66f34_19c40a1a_804906ed" note that the quotes are required is the shared secret we have generated above with the command ipsec ranbits 256 > temp in the temp file.

The files ipsec.conf and ipsec.secrets must be copied to the second gateway machine so as to be identical on both ends. The only exception to this is the ipsec.conf file, which must have in it a section labeled by the line config setup with the correct interface settings for the second gateway, if they differ from the first. The ipsec.secrets file, contrary to the RSA private key, should absolutely have the same-shared secrets on the two gateways.