The device creating or modifying the VTP configuration
signs it using the MD5 digest generated from the secret
key before advertising it. Other devices in the domain
receiving this configuration use the same secret key
to accept it if it was correctly signed or drop it
otherwise.
By default, the object has the value as a zero-length
string and this value is read only. It is set
to this value automatically when the password
(vtpAuthPassword) is set to a zero-length octet string.
The secret key can be either generated using
the password or configured by the user. Once
the secret key is configured by the user, it is
stored as a hexadecimal string in the device's
configuration and the password is considered to be
the secret key's matching password and hidden
from the configuration automatically.
This object is not allowed to be set at the same
time when vtpAuthPassword is set.
The secret key is overwritten by a newly generated
secret key when the password is re-configured.