GSSAPI Key Exchange Patch for OpenSSH 5.0p1 (plus an added extra)
Simon Wilkinson
sxw at inf.ed.ac.uk
Fri Apr 4 10:03:49 EDT 2008
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It's that time again! There's been another OpenSSH release, and once
again, I'm pleased to announce the availability of my GSSAPI Key
Exchange patch for it.
Whilst OpenSSH contains support for GSSAPI user authentication, this
still relies upon SSH host keys to authenticate the server to the
user. For sites with a deployed Kerberos infrastructure this adds an
additional, unnecessary, key management burden. GSSAPI key exchange
allows the use of security mechanisms such as Kerberos to
authenticate the server to the user, removing the need for trusted
ssh host keys, and allowing the use of a single security architecture.
This patch adds support for the RFC4462 GSSAPI key exchange
mechanisms to OpenSSH, along with adding some additional, generic,
GSSAPI features. It implements
*) gss-group1-sha1-*, gss-group14-sha1-* and gss-gex-sha1-* key
exchange mechanisms. (#1242)
*) Support for the null host key type (#1242)
*) Support for CCAPI credentials caches on Mac OS X (#1245)
*) Support for better error handling when an authentication
exchange fails due to server misconfiguration (#1244)
*) Support for GSSAPI connections to hosts behind a round-robin
load balancer (#1008)
*) Support for GSSAPI connections to multi-homed hosts, where each
interface has a unique name (#928)
(bugzilla.mindrot.org bug numbers are in brackets)
This release fixes a problem where the GSSAPIStrictAcceptorCheck
option was always enabled.
As usual, the code is available from http://www.sxw.org.uk/computing/
patches/openssh.html
In addition, with this release I'm pleased to be able to announce an
additional patch which implements cascading credential support. This
allows credentials provided via key exchange to be cascaded through a
set of ssh connections, so that a once a user reauthenticates on
their workstation, the new credentials are available on all machines
to which they are currently connected. This is controlled via the new
options GSSAPIRenewalForcesReKey and GSSAPIStoreCredentialsOnRekey. A
pam stack, 'sshd-rekey' may be defined to trigger renewal of
additional credentials, such as X509 certificates or AFS tokens, when
credentials are renewed on a particular machine. Cascading credential
support is implemented using the standard ssh protocol.
The cascading credentials patch is also available from the above
website. Whilst it has been extensively tested, it has received less
peer-review than the rest of the GSSAPI code. Reports of both
success, and failure, would be greatly appreciated! If anyone would
like to provide face-to-face feedback, I will be at the AFS &
Kerberos Best Practices Workshop in May.
Cheers,
Simon.
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