OpenSolaris

SMB/CIFS servers support packet signing these days, i.e. the ability to
use Kerberos services to add a cryptographic hash to a message such that
the message integrity can be assured in mutual authentication.  We have
committed to PSARC to investigate this, though it is not required.
Some clarifications of the previous:  Kerberos is not necessarily involved.
"SMB signing" is a method for ensuring packet integrity, which includes an
MD5 "signature" in each message.  This feature is further described here:
  "Overview of Server Message Block signing"
  http://support.microsoft.com/kb/887429

The following table shows how the new "signing" parameter
works in conjunction with the server's settings to decide
whether communications will be signed or not, and in which
cases communications will be declined (Fail).

 * cli/srv  | Required | Enabled    | Disabled
 * ---------+----------+------------+-----------
 * Required | Signed   | Signed     |  Fail
 * ---------+----------+------------+-----------
 * Enabled  | Signed   | Signed     | Not Signed
 * ---------+----------+------------+-----------
 * Disabled | Fail     | Not Signed | Not Signed

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