mirror of git://anongit.mindrot.org/openssh.git
123 lines
4.9 KiB
Plaintext
123 lines
4.9 KiB
Plaintext
[ A Japanese translation of this document is available at
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[ http://www.unixuser.org/%7Eharuyama/security/openssh/index.html
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[ Thanks to HARUYAMA Seigo <haruyama@nt.phys.s.u-tokyo.ac.jp>
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OpenSSH is almost completely compatible with the commercial SSH 1.2.x.
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There are, however, a few exceptions that you will need to bear in
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mind while upgrading:
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1. OpenSSH does not support any patented transport algorithms.
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Only 3DES and Blowfish can be selected. This difference may manifest
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itself in the ssh command refusing to read its config files.
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Solution: Edit /etc/ssh/ssh_config and select a different "Cipher"
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option ("3des" or "blowfish").
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2. Old versions of commercial SSH encrypt host keys with IDEA
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The old versions of SSH used a patented algorithm to encrypt their
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/etc/ssh/ssh_host_key
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This problem will manifest as sshd not being able to read its host
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key.
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Solution: You will need to run the *commercial* version of ssh-keygen
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on the host's private key:
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ssh-keygen -u -f /etc/ssh/ssh_host_key
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3. Incompatible changes to sshd_config format.
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OpenSSH extends the sshd_config file format in a number of ways. There
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is currently one change which is incompatible with the old.
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Commercial SSH controlled logging using the "QuietMode" and
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"FascistLogging" directives. OpenSSH introduces a more general set of
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logging options "SyslogFacility" and "LogLevel". See the sshd manual
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page for details.
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4. Warning messages about key lengths
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Commercial SSH's ssh-keygen program contained a bug which caused it to
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occasionally generate RSA keys which had their Most Significant Bit
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(MSB) unset. Such keys were advertised as being full-length, but are
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actually only half as secure.
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OpenSSH will print warning messages when it encounters such keys. To
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rid yourself of these message, edit you known_hosts files and replace
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the incorrect key length (usually "1024") with the correct key length
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(usually "1023").
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5. Spurious PAM authentication messages in logfiles
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OpenSSH will generate spurious authentication failures at every login,
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similar to "authentication failure; (uid=0) -> root for sshd service".
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These are generated because OpenSSH first tries to determine whether a
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user needs authentication to login (e.g. empty password). Unfortunatly
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PAM likes to log all authentication events, this one included.
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If it annoys you too much, set "PermitEmptyPasswords no" in
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sshd_config. This will quiet the error message at the expense of
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disabling logins to accounts with no password set. This is the
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default if you use the supplied sshd_config file.
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6. Empty passwords not allowed with PAM authentication
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To enable empty passwords with a version of OpenSSH built with PAM you
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must add the flag "nullok" to the end of the password checking module
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in the /etc/pam.d/sshd file. For example:
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auth required/lib/security/pam_unix.so shadow nodelay nullok
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This must be done in addtion to setting "PermitEmptyPasswords yes"
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in the sshd_config file.
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There is one caveat when using empty passwords with PAM
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authentication: PAM will allow _any_ password when authenticating
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an account with an empty password. This breaks the check that sshd
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uses to determined whether an account has no password set and grant
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users access to the account regardless of the policy specified by
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"PermitEmptyPasswords". For this reason, it is recommended that you do
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not add the "nullok" directive to your PAM configuration file unless
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you specifically wish to allow empty passwords.
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7. X11 and/or agent forwarding does not work
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Check your ssh_config and sshd_config. The default configuration files
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disable authentication agent and X11 forwarding.
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8. ssh takes a long time to connect with Linux/glibc 2.1
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The glibc shipped with Redhat 6.1 appears to take a long time to resolve
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"IPv6 or IPv4" addresses from domain names. This can be kludged around
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with the --with-ipv4-default configure option. This instructs OpenSSH to
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use IPv4-only address resolution. (IPv6 lookups may still be made by
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specifying the -6 option).
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9. Logins from commercial ssh generate the error "Selected cipher type
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idea not supported by server"
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This error is generated when a commercial ssh which has been configured to
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use the 'idea' cipher attempts to connect to an OpenSSH server. To rectify
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this, select a different cipher in ssh_config or ~/.ssh/config (3des for
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security or blowfish for speed).
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10. "can't locate module net-pf-10" messages in log under Linux
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The Linux kernel is looking (via modprobe) for protocol family 10 (IPv6).
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Either 1. load the appropriate kernel module, 2. enter the correct alias
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in /etc/modules.conf or 3. disable IPv6 in /etc/modules.conf.
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For some silly reason /etc/modules.conf may also be named /etc/conf.modules
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11. Password authentication doesn't work on Slackware 7.0
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Configure OpenSSH with --with-md5-passwords
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12. ./configure or sshd complain about lack of RSA support
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Ensure that your OpenSSL libraries have been built to include RSA support
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either internally or through RSAref.
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