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About This Document >>     Installing SSH Tectia Server for IBM z/OS >>     Using SSH Tectia Server for IBM z/OS >>     Configuring the Server >>     Configuring the Client >>     Authentication >>         Server Authentication with Public Keys >>         User Authentication with Passwords         User Authentication with Public Keys >>             Using Public-Key Authentication from z/OS Client             Using Public-Key Authentication from Windows Client to z/OS Server             Using Public-Key Authentication from Unix Client to z/OS Server             z/OS Server Configuration             Optional Configuration Settings         Host-Based User Authentication >>         User Authentication with Keyboard-Interactive >>     Troubleshooting SSH Tectia Server for IBM z/OS >>     Examples of Use >>     Man Pages >>     Log Messages >>

Using Public-Key Authentication from z/OS Client

All commands in this section are shown using the SSH Tectia z/OS client. Server-side configuration can also be done by logging in to the remote server and entering the commands locally.

To set up user public-key authentication from a z/OS Client, do the following steps:

1. Create a key pair by executing ssh-keygen2 on the z/OS client host.

   By default, ssh-keygen2 creates a 2048-bit DSA key pair. RSA keys can be generated by specifying the -t rsa option. Key length can be specified with the -b option. For non-interactive use, the key can be generated without a passphrase with the -P option.

   $ /usr/lpp/ssh2/bin/ssh-keygen2 -t rsa -b 1024 -P $HOME/.ssh2/mf_key
   Generating 1024-bit rsa key pair
      2 oOo.oOo.oOo.
   Key generated.
   1024-bit rsa, TESTUSER@ZOS, Tue Jul 11 2006 01:45:06 -0600
   Private key saved to /u/TESTUSER/.ssh2/mf_key
   Public key saved to /u/TESTUSER/.ssh2/mf_key.pub
   

   If the -P option is not used, ssh-keygen2 asks for a passphrase for the new key.

   ssh-keygen2 stores your new authentication key pair in two separate files. One of the keys is your private key which must never be made available to anyone but yourself.

   In the example above, the private key file is mf_key. The other file mf_key.pub is your public key, which can be distributed to other computers.

   For more information on the ssh-keygen2 options, see the ssh-keygen2 man page (Appendix ssh-keygen2).

2. Create an identification file in your $HOME/.ssh2 directory on the z/OS Client, for example:

   $ cd $HOME/.ssh2
   $ echo "IdKey mf_key" >identification
   $ cat identification 
   IdKey mf_key
   

   You now have an identification file that consists of one line that denotes the file containing your identification (your private key). For special applications, you can create multiple identifications by executing ssh-keygen2 again. However, this is not usually needed.
3. Create a .ssh2 or .ssh directory on Server (if it does not exist already).
   • If the remote host is running SSH Tectia Server on Unix or z/OS :

     $ ssh2 testuser@tectia_server mkdir .ssh2
     

   • If the remote host is running SSH Tectia Server on Windows:

     $ ssh2 testuser@tectia_win_server "cmd /c mkdir .ssh2"
     

   • If the remote host is running OpenSSH on Unix or z/OS:

     $ ssh2 testuser@openssh_server mkdir .ssh
     

4. Copy your public key to Server.
   • Keys created with z/OS ssh-keygen2 are in stored in the EBCDIC format. When the public key is transferred to a Unix or Windows server, it must be converted to the ASCII format.

     $ scp2 /ftadv:C=ISO8859-1,D=IBM-1047,X=TEXT/mf_key.pub 
     testuser@tectia_server:.ssh2/
     

     or

     $ scp2 /ftadv:C=ISO8859-1,D=IBM-1047,X=TEXT/mf_key.pub 
     testuser@Openssh_server:.ssh/
     

   • If public-key authentication is configured between mainframe servers, conversion is not needed. To ensure that key stays in EBCDIC format, binary file transfer should be used.

     $ scp2 /ftadv:X=BIN/mf_key.pub 
     testuser@tectia_server:/ftadv:X=BIN/.ssh2/
     

     or

     $ scp2 /ftadv:X=BIN/mf_key.pub testuser@openssh_server:.ssh
     

5. Create an authorization or authorized_keys file on Server.
   • If the remote host is running SSH Tectia Server, the key entry needs to be added to authorization file.

     $ ssh2 testuser@tectia_unix_server "echo Key mf_key.pub > 
     .ssh2/authorization"
     

     or

     $ ssh2 testuser@tectia_win_server "cmd /c echo Key mf_key.pub  > 
     .ssh2/authorization"
     

   • If the remote host is running OpenSSH, the key has to be converted to the OpenSSH key format and concatenated to the authorized_keys file.

     $ ssh2 testuser@open_server "ssh-keygen -I -f .ssh/mf_key.pub >> 
     .ssh/authorized_keys"
     

6. Make sure the AllowedAuthentications keyword in the /etc/ssh2/ssh2_config file (or the $HOME/.ssh2/ssh2_config file) on the z/OS client contains the argument publickey:

   AllowedAuthentications publickey

   Other authentication methods can be listed in the configuration file as well.