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Catch up with the SSH1 code removal and delete all
mention of protocol 1 particularities, key files and formats, command line
options, and configuration keywords from the server documentation and
examples.  ok jmc@

Upstream-ID: 850328854675b4b6a0d4a90f0b4a9dd9ca4e905f
This commit is contained in:
naddy@openbsd.org 2016-08-15 12:32:04 +00:00 committed by Damien Miller
parent c38ea63489
commit ffe6549c2f
3 changed files with 29 additions and 168 deletions
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108
sshd.8
View File

@ -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.8,v 1.284 2016/02/17 07:38:19 jmc Exp $
.Dd $Mdocdate: February 17 2016 $
.\" $OpenBSD: sshd.8,v 1.285 2016/08/15 12:32:04 naddy Exp $
.Dd $Mdocdate: August 15 2016 $
.Dt SSHD 8
.Os
.Sh NAME
@ -44,14 +44,12 @@
.Nm sshd
.Bk -words
.Op Fl 46DdeiqTt
.Op Fl b Ar bits
.Op Fl C Ar connection_spec
.Op Fl c Ar host_certificate_file
.Op Fl E Ar log_file
.Op Fl f Ar config_file
.Op Fl g Ar login_grace_time
.Op Fl h Ar host_key_file
.Op Fl k Ar key_gen_time
.Op Fl o Ar option
.Op Fl p Ar port
.Op Fl u Ar len
@ -96,9 +94,6 @@ to use IPv4 addresses only.
Forces
.Nm
to use IPv6 addresses only.
.It Fl b Ar bits
Specifies the number of bits in the ephemeral protocol version 1
server key (default 1024).
.It Fl C Ar connection_spec
Specify the connection parameters to use for the
.Fl T
@ -169,36 +164,18 @@ This option must be given if
is not run as root (as the normal
host key files are normally not readable by anyone but root).
The default is
.Pa /etc/ssh/ssh_host_key
for protocol version 1, and
.Pa /etc/ssh/ssh_host_dsa_key ,
.Pa /etc/ssh/ssh_host_ecdsa_key .
.Pa /etc/ssh/ssh_host_ecdsa_key ,
.Pa /etc/ssh/ssh_host_ed25519_key
and
.Pa /etc/ssh/ssh_host_rsa_key
for protocol version 2.
.Pa /etc/ssh/ssh_host_rsa_key .
It is possible to have multiple host key files for
the different protocol versions and host key algorithms.
the different host key algorithms.
.It Fl i
Specifies that
.Nm
is being run from
.Xr inetd 8 .
If SSH protocol 1 is enabled,
.Nm
should not normally be run
from inetd because it needs to generate the server key before it can
respond to the client, and this may take some time.
Clients may have to wait too long if the key was regenerated every time.
.It Fl k Ar key_gen_time
Specifies how often the ephemeral protocol version 1 server key is
regenerated (default 3600 seconds, or one hour).
The motivation for regenerating the key fairly
often is that the key is not stored anywhere, and after about an hour
it becomes impossible to recover the key for decrypting intercepted
communications even if the machine is cracked into or physically
seized.
A value of zero indicates that the key will never be regenerated.
.It Fl o Ar option
Can be used to give options in the format used in the configuration file.
This is useful for specifying options for which there is no separate
@ -257,8 +234,7 @@ may also be used to prevent
from making DNS requests unless the authentication
mechanism or configuration requires it.
Authentication mechanisms that may require DNS include
.Cm RhostsRSAAuthentication ,
.Cm HostbasedAuthentication ,
.Cm HostbasedAuthentication
and using a
.Cm from="pattern-list"
option in a key file.
@ -269,42 +245,14 @@ or
.Cm DenyUsers .
.El
.Sh AUTHENTICATION
The OpenSSH SSH daemon supports SSH protocols 1 and 2.
The default is to use protocol 2 only,
though this can be changed via the
.Cm Protocol
option in
.Xr sshd_config 5 .
Protocol 1 should not be used
and is only offered to support legacy devices.
.Pp
The OpenSSH SSH daemon supports SSH protocol 2 only.
Each host has a host-specific key,
used to identify the host.
Partial forward security for protocol 1 is provided through
an additional server key,
normally 1024 bits,
generated when the server starts.
This key is normally regenerated every hour if it has been used, and
is never stored on disk.
Whenever a client connects, the daemon responds with its public
host and server keys.
host key.
The client compares the
RSA host key against its own database to verify that it has not changed.
The client then generates a 256-bit random number.
It encrypts this
random number using both the host key and the server key, and sends
the encrypted number to the server.
Both sides then use this
random number as a session key which is used to encrypt all further
communications in the session.
The rest of the session is encrypted
using a conventional cipher, currently Blowfish or 3DES, with 3DES
being used by default.
The client selects the encryption algorithm
to use from those offered by the server.
.Pp
For protocol 2,
forward security is provided through a Diffie-Hellman key agreement.
host key against its own database to verify that it has not changed.
Forward security is provided through a Diffie-Hellman key agreement.
This key agreement results in a shared session key.
The rest of the session is encrypted using a symmetric cipher, currently
128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
@ -477,32 +425,25 @@ key (empty lines and lines starting with a
.Ql #
are ignored as
comments).
Protocol 1 public keys consist of the following space-separated fields:
options, bits, exponent, modulus, comment.
Protocol 2 public key consist of:
Public keys consist of the following space-separated fields:
options, keytype, base64-encoded key, comment.
The options field is optional;
its presence is determined by whether the line starts
with a number or not (the options field never starts with a number).
The bits, exponent, modulus, and comment fields give the RSA key for
protocol version 1; the
comment field is not used for anything (but may be convenient for the
user to identify the key).
For protocol version 2 the keytype is
The options field is optional.
The keytype is
.Dq ecdsa-sha2-nistp256 ,
.Dq ecdsa-sha2-nistp384 ,
.Dq ecdsa-sha2-nistp521 ,
.Dq ssh-ed25519 ,
.Dq ssh-dss
or
.Dq ssh-rsa .
.Dq ssh-rsa ;
the comment field is not used for anything (but may be convenient for the
user to identify the key).
.Pp
Note that lines in this file are usually several hundred bytes long
Note that lines in this file can be several hundred bytes long
(because of the size of the public key encoding) up to a limit of
8 kilobytes, which permits DSA keys up to 8 kilobits and RSA
keys up to 16 kilobits.
You don't want to type them in; instead, copy the
.Pa identity.pub ,
.Pa id_dsa.pub ,
.Pa id_ecdsa.pub ,
.Pa id_ed25519.pub ,
@ -511,8 +452,7 @@ or the
file and edit it.
.Pp
.Nm
enforces a minimum RSA key modulus size for protocol 1
and protocol 2 keys of 768 bits.
enforces a minimum RSA key modulus size of 768 bits.
.Pp
The options (if present) consist of comma-separated option
specifications.
@ -690,7 +630,7 @@ maintained automatically: whenever the user connects from an unknown host,
its key is added to the per-user file.
.Pp
Each line in these files contains the following fields: markers (optional),
hostnames, bits, exponent, modulus, comment.
hostnames, keytype, base64-encoded key, comment.
The fields are separated by spaces.
.Pp
The marker is optional, but if it is present then it must be one of
@ -731,9 +671,9 @@ character.
Only one hashed hostname may appear on a single line and none of the above
negation or wildcard operators may be applied.
.Pp
Bits, exponent, and modulus are taken directly from the RSA host key; they
The keytype and base64-encoded key are taken directly from the host key; they
can be obtained, for example, from
.Pa /etc/ssh/ssh_host_key.pub .
.Pa /etc/ssh/ssh_host_rsa_key.pub .
The optional comment field continues to the end of the line, and is not used.
.Pp
Lines starting with
@ -772,8 +712,8 @@ Note that the lines in these files are typically hundreds of characters
long, and you definitely don't want to type in the host keys by hand.
Rather, generate them by a script,
.Xr ssh-keyscan 1
or by taking
.Pa /etc/ssh/ssh_host_key.pub
or by taking, for example,
.Pa /etc/ssh/ssh_host_rsa_key.pub
and adding the host names at the front.
.Xr ssh-keygen 1
also offers some basic automated editing for
@ -912,7 +852,6 @@ This file is used in exactly the same way as
but allows host-based authentication without permitting login with
rlogin/rsh.
.Pp
.It Pa /etc/ssh/ssh_host_key
.It Pa /etc/ssh/ssh_host_dsa_key
.It Pa /etc/ssh/ssh_host_ecdsa_key
.It Pa /etc/ssh/ssh_host_ed25519_key
@ -924,7 +863,6 @@ Note that
.Nm
does not start if these files are group/world-accessible.
.Pp
.It Pa /etc/ssh/ssh_host_key.pub
.It Pa /etc/ssh/ssh_host_dsa_key.pub
.It Pa /etc/ssh/ssh_host_ecdsa_key.pub
.It Pa /etc/ssh/ssh_host_ed25519_key.pub

17
sshd_config
View File

@ -1,4 +1,4 @@
# $OpenBSD: sshd_config,v 1.99 2016/07/11 03:19:44 tedu Exp $
# $OpenBSD: sshd_config,v 1.100 2016/08/15 12:32:04 naddy Exp $
# This is the sshd server system-wide configuration file. See
# sshd_config(5) for more information.
@ -15,21 +15,11 @@
#ListenAddress 0.0.0.0
#ListenAddress ::
# The default requires explicit activation of protocol 1
#Protocol 2
# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key
#HostKey /etc/ssh/ssh_host_ed25519_key
# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h
#ServerKeyBits 1024
# Ciphers and keying
#RekeyLimit default none
@ -45,7 +35,6 @@
#MaxAuthTries 6
#MaxSessions 10
#RSAAuthentication yes
#PubkeyAuthentication yes
# The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
@ -58,11 +47,9 @@ AuthorizedKeysFile .ssh/authorized_keys
#AuthorizedKeysCommandUser nobody
# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#RhostsRSAAuthentication no
# similar for protocol version 2
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# RhostsRSAAuthentication and HostbasedAuthentication
# HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes

72
sshd_config.5
View File

@ -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 1.228 2016/08/12 19:19:04 jca Exp $
.Dd $Mdocdate: August 12 2016 $
.\" $OpenBSD: sshd_config.5,v 1.229 2016/08/15 12:32:04 naddy Exp $
.Dd $Mdocdate: August 15 2016 $
.Dt SSHD_CONFIG 5
.Os
.Sh NAME
@ -230,8 +230,6 @@ of
.Dq publickey,publickey
will require successful authentication using two different public keys.
.Pp
This option will yield a fatal
error if enabled if protocol 1 is also enabled.
Note that each authentication method listed should also be explicitly enabled
in the configuration.
The default
@ -709,15 +707,12 @@ is not to load any certificates.
.It Cm HostKey
Specifies a file containing a private host key
used by SSH.
The default is
.Pa /etc/ssh/ssh_host_key
for protocol version 1, and
The defaults are
.Pa /etc/ssh/ssh_host_dsa_key ,
.Pa /etc/ssh/ssh_host_ecdsa_key ,
.Pa /etc/ssh/ssh_host_ed25519_key
and
.Pa /etc/ssh/ssh_host_rsa_key
for protocol version 2.
.Pa /etc/ssh/ssh_host_rsa_key .
.Pp
Note that
.Xr sshd 8
@ -728,14 +723,6 @@ option restricts which of the keys are actually used by
.Xr sshd 8 .
.Pp
It is possible to have multiple host key files.
.Dq rsa1
keys are used for version 1 and
.Dq dsa ,
.Dq ecdsa ,
.Dq ed25519
or
.Dq rsa
are used for version 2 of the SSH protocol.
It is also possible to specify public host key files instead.
In this case operations on the private key will be delegated
to an
@ -774,8 +761,6 @@ Specifies that
and
.Pa .shosts
files will not be used in
.Cm RhostsRSAAuthentication
or
.Cm HostbasedAuthentication .
.Pp
.Pa /etc/hosts.equiv
@ -790,8 +775,6 @@ Specifies whether
should ignore the user's
.Pa ~/.ssh/known_hosts
during
.Cm RhostsRSAAuthentication
or
.Cm HostbasedAuthentication .
The default is
.Dq no .
@ -910,15 +893,6 @@ option of
.Xr ssh 1
with an argument of
.Dq kex .
.It Cm KeyRegenerationInterval
In protocol version 1, the ephemeral server key is automatically regenerated
after this many seconds (if it has been used).
The purpose of regeneration is to prevent
decrypting captured sessions by later breaking into the machine and
stealing the keys.
The key is never stored anywhere.
If the value is 0, the key is never regenerated.
The default is 3600 (seconds).
.It Cm ListenAddress
Specifies the local addresses
.Xr sshd 8
@ -1127,8 +1101,6 @@ Available keywords are
.Cm PubkeyAuthentication ,
.Cm RekeyLimit ,
.Cm RevokedKeys ,
.Cm RhostsRSAAuthentication ,
.Cm RSAAuthentication ,
.Cm StreamLocalBindMask ,
.Cm StreamLocalBindUnlink ,
.Cm TrustedUserCAKeys ,
@ -1333,28 +1305,6 @@ when a user logs in interactively.
or equivalent.)
The default is
.Dq yes .
.It Cm Protocol
Specifies the protocol versions
.Xr sshd 8
supports.
The possible values are
.Sq 1
and
.Sq 2 .
Multiple versions must be comma-separated.
The default is
.Sq 2 .
Protocol 1 suffers from a number of cryptographic weaknesses and should
not be used.
It is only offered to support legacy devices.
.Pp
Note that the order of the protocol list does not indicate preference,
because the client selects among multiple protocol versions offered
by the server.
Specifying
.Dq 2,1
is identical to
.Dq 1,2 .
.It Cm PubkeyAcceptedKeyTypes
Specifies the key types that will be accepted for public key authentication
as a comma-separated pattern list.
@ -1419,20 +1369,6 @@ an OpenSSH Key Revocation List (KRL) as generated by
.Xr ssh-keygen 1 .
For more information on KRLs, see the KEY REVOCATION LISTS section in
.Xr ssh-keygen 1 .
.It Cm RhostsRSAAuthentication
Specifies whether rhosts or /etc/hosts.equiv authentication together
with successful RSA host authentication is allowed.
The default is
.Dq no .
This option applies to protocol version 1 only.
.It Cm RSAAuthentication
Specifies whether pure RSA authentication is allowed.
The default is
.Dq yes .
This option applies to protocol version 1 only.
.It Cm ServerKeyBits
Defines the number of bits in the ephemeral protocol version 1 server key.
The default and minimum value is 1024.
.It Cm StreamLocalBindMask
Sets the octal file creation mode mask
.Pq umask