upstream commit
remember which public keys have been used for
authentication and refuse to accept previously-used keys.
This allows AuthenticationMethods=publickey,publickey to require
that users authenticate using two _different_ pubkeys.
ok markus@
diff --git a/sshd_config.5 b/sshd_config.5
index 938ba2f..d2ab281 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -33,8 +33,8 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.\" $OpenBSD: sshd_config.5,v 1.184 2014/12/21 23:35:14 jmc Exp $
-.Dd $Mdocdate: December 21 2014 $
+.\" $OpenBSD: sshd_config.5,v 1.185 2014/12/22 07:51:30 djm Exp $
+.Dd $Mdocdate: December 22 2014 $
.Dt SSHD_CONFIG 5
.Os
.Sh NAME
@@ -210,6 +210,18 @@
.Dq bsdauth
device.
.Pp
+If the
+.Dq publickey
+method is listed more than one,
+.Xr sshd 8
+verifies that keys that have been used successfully are not reused for
+subsequent authentications.
+For example, an
+.Cm AuthenticationMethods
+of
+.Dq publickey,publickey
+will require successful authentication using two different public keys.
+.Pp
This option is only available for SSH protocol 2 and will yield a fatal
error if enabled if protocol 1 is also enabled.
Note that each authentication method listed should also be explicitly enabled