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Summary: Port of OpenBSD's free SSH release
- Disable EC/RC5 algorithms in OpenSSL for patent reasons.
- Enable high performance ssh
- Add support for storing SSH public keys in LDAP
- Use LDNS for DNSSEC/SSHFP validation.
- Support for Stream Control Transmission Protocol
- Support the legacy/weak SSH1 protocol
- Enable additional crypto algorithms via OpenSSL
- Adds support for X.509 certificate authentication
SSH is a cryptographically confidential network protocol for data transmission between 2 networked computers. There are 2 protocol versions; SSH-1 and SSH-2.
Funtoo uses the OpenSSH daemon (sshd) to provide the SSH service by default. sshd is a member of OpenRC's default runlevel.
By default login is allowed for all users via the ssh daemon on port 22 with any valid username and password combination.
There are 2 means of configuring
sshd. The first is required, the second is optional.
sshdreads its configuration data from
sshdmay be configured to use PAM.
Permission may be granted or denied via PAM, allowing you to store usernames etc. using text files.
Protocol version selection
The default protocol version is SSH-2. SSH-1 requires explicit activation. To select a protocol version, use the
Ciphers directive specifies the ciphers allowed for protocol version 2.
Single authentication method
- Password authentication
This is enabled by default, it is configured using the
PasswordAuthenticationdirective. Valid parameters are
PasswordAuthentication yesis configured, the state of the
PermitEmptyPasswordsdirective is evaluated.
- Public key authentication
This is enabled with combinations of
On your client, run
# ssh-keygen -t rsa
This command will generate a public and private key, stored at
~/.ssh/id_rsa respectively. The private key should not be shared with anyone. The pubilc key can be freely shared, and can only be used to grant you access to remote systems by use of your private key. To grant yourself access to a remote account, append the contents of
~/.ssh/id_rsa.pub to the file
~/.ssh/authorized_keys on a remote system. Note that
~/.ssh/authorized_keys must not be readable by anyone but the user for OpenSSH to process the file -- do this by running
chmod -R go-rwx ~/.ssh on the remote system.
Providing a passphrase for your private key will cause it to be stored in an encrypted format, using this passphrase. Before you can use your private key, you will be prompted by OpenSSH to type in this passphrase. This is similar to typing in a password, but with the use of this authentication method, your password is not sent over the network at all.
ssh-agent exists to allow decrypted private keys to be cached in memory for easy access, so you do not need to type in your passphrase every time. It can still be quite complex to use, so it's recommended to use a front-end for
ssh-agent -- see the Keychain page to learn about such a tool. Keychain is also part of Funtoo.
Create a user, or select which user the client will be accessing the server as, then place clients id_rsa.pub file into the users
Single Machine Testing
# ssh-keygen -t rsa
Press enter several times to accept default settings.
# cp ~/.ssh/id_rsa.pub ~/.ssh/authorized_keys
# ssh localhost
- Host-based authentication
Requiring multiple authentication factors
These options are only available for SSH-2. The default is not to require multiple authentication. To identify to the daemon that you wish to require more than one authentication, you must use the
AuthenticationMethods directive. This directive is followed by one or more comma separated lists of authentication method names. Lists are separated with a space. Successful authentication requires completion of every method in at least one of these lists.
AuthenticationMethods "password,publickey password,keyboard-interactive"
Password authentication using
The following 4 directives are listed in order of evaluation by OpenSSH. They are configured directly; within
sshd_config. Only user or group _names_ are valid, numerical IDs are not recognized. If the pattern takes the form
USER@HOST then access is restricted to the
USER when originating from the
DenyUsers PATTERN PATTERN ...
- Login is forbidden for users whose username matches one of the patterns
AllowUsers PATTERN PATTERN ...
- Login is permitted to users whose username matches one of the patterns
DenyGroups PATTERN PATTERN ...
- Login is forbidden for users whose primary group or supplementary group list matches one of the patterns
AllowGroups PATTERN PATTERN ...
- Login is permitted to users whose primary group or supplementary group list matches one of the patterns
Public key authentication
Host based authentication
Controlling root access
Access by the root user can be controlled using the
Permit empty passwords
Access to accounts with empty (i.e. blank) passwords can be controlled using the
GSSAPIAuthenticaion GSSAPICleanupCredentials GSSAPIStrictAcceptorCheck HostBasedAuthentication HostBasedUsesNameFromPacketOnly HostCertificate HostKey HostKeyAgent LoginGraceTime MAC MaxAuthTries MaxSessions MaxStartups PasswordAuthentication PermitEmptyPasswords PubkeyAuthentication RevokedKeys RhostsRSAAuthentication RSAAuthentication TrustedUserCAKeys UseLogin UsePAM
By default X11 forwarding is disabled in OpenSSHd,
If you would like to forward X11 from your Funtoo box to a remote system you must first edit your /etc/ssh/sshd_config file
#X11Forwarding no #X11DisplayOffset 10 #X11UseLocalhost yes
X11Forwarding yes X11DisplayOffset 10 X11UseLocalhost yes
X forwarding will now be enabled from that machine, so if you connect from your remote with 'ssh -X <user>@<ipaddress>' X sessions will be forwarded
ssh is a commonly attacked service. Package:Sshguard monitors logs, and black list remote users who have repeatedly failed to login.