Fetching Remote Server Keys

Tectia client tools for z/OS must have the remote server public keys or public key hash values available in order to authenticate the remote server they are connecting to. The keys or key hash values can be stored in the mainframe user's $HOME/.ssh2/hostkeys directory or in the /opt/tectia/etc/hostkeys directory which is common for all the users. The key distribution tool can be used to retrieve multiple remote host keys and store the keys or key hash values to the user's host key directory or to the system-wide key store that is available for all the users.

For more information about hashed host key format, see Host Key Storage Formats.

Examples of Fetching Remote Server Keys

The following examples illustrate using ssh-keydist-g3 for fetching remote server host keys.

	Caution
	When ssh-keydist-g3 is run with the `-N` (alias for `--accept-host-keys`) option, it accepts the received host keys automatically without prompting the user. You should verify the validity of keys after receiving them or you risk being subject to a man-in-the-middle attack.

Example 1: Using USS

This example is run under the USS shell. Multiple host keys are fetched in verbose mode and saved in plain format under the user's $HOME/.ssh2/hostkeys directory. The host keys are also saved using the IP addresses of the hosts. The log is stored under /tmp. The log will list the accepted keys and their fingerprints. You should verify them after running the command.

$ ssh-keydist-g3 --verbose --accept-host-keys --accept-host-keys-also-by-ip \ 
--accepted-host-key-filename-format plain \
--accepted-host-key-log /tmp/newhosts.log \ 
host1 host2 host3

Example 2: Using JCL

This example HOSTSAVE from /opt/tectia/doc/zOS/SAMPLIB presents a JCL script that does the same steps as the USS command in Example 1 above (the options are given in short format):

//HOSTSAVE EXEC PGM=IKJEFT1A,
//             REGION=0M
//SYSTSPRT DD  SYSOUT=*
//STDOUT   DD  PATH='/tmp/&SYSUID.-HOSTSAVE.out',
//             PATHOPTS=(OWRONLY,OCREAT,OTRUNC),
//             PATHMODE=(SIRUSR,SIWUSR)
//STDERR   DD  PATH='/tmp/&SYSUID.-HOSTSAVE.err',
//             PATHOPTS=(OWRONLY,OCREAT,OTRUNC),
//             PATHMODE=(SIRUSR,SIWUSR)
//STDENV   DD  DSN=&SYSUID..SSZ.SRVR63.PARMLIB(SSHENV),
//             DISP=SHR
//SYSTSIN  DD  *
  BPXBATCH SH  /opt/tectia/bin/ssh-keydist-g3 +
               -v -N -i -F plain -A /tmp/newhosts.log +
               host1 host2 host3
/*
//*
//PROUT   EXEC PGM=IKJEFT1A,
//             PARM='OCOPY INDD(STDOUT) OUTDD(STDOUTPR) TEXT'
//SYSTSPRT DD  SYSOUT=*
//SYSTSIN  DD  DUMMY
//STDOUT   DD  PATH='/tmp/&SYSUID.-HOSTSAVE.out',
//             PATHOPTS=(ORDONLY),
//             PATHDISP=(DELETE,KEEP),
//             PATHMODE=(SIRUSR,SIWUSR)
//STDOUTPR DD  SYSOUT=*,
//             DCB=(LRECL=4000,RECFM=VB)
//*
//PRERR   EXEC PGM=IKJEFT1A,
//             PARM='OCOPY INDD(STDERR) OUTDD(STDERRPR) TEXT'
//SYSTSPRT DD  SYSOUT=*
//SYSTSIN  DD  DUMMY
//STDERR   DD  PATH='/tmp/&SYSUID.-HOSTSAVE.err',
//             PATHOPTS=(ORDONLY),
//             PATHDISP=(DELETE,KEEP),
//             PATHMODE=(SIRUSR,SIWUSR)
//STDERRPR DD  SYSOUT=*,
//             DCB=(LRECL=4000,RECFM=VB)
//*