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       encode_keychange - produce the KeyChange string for SNMPv3


       encode_keychange -t md5|sha1 [OPTIONS]


       encode_keychange  produces  a  KeyChange  string  using the old and new
       passphrases as described in Section 5 of RFC 2274 "User-based  Security
       Model  (USM)  for  version  3 of the Simple Network Management Protocol
       (SNMPv3)". -t option is mandatory and specifies the hash transform type
       to use.

       The  transform  is used to convert passphrase to master key for a given
       user (Ku), convert master key to the localized key (Kul), and  to  hash
       the old Kul with the random bits.

       Passphrases are obtained by examining a number of sources until success
       (in order listed):

              command line options (see -N and -O options below);

              the file $HOME/.snmp/passphrase.ek which should only contain two
              lines with old and new passphrase;

              standard input -or-  user input from the terminal.


       -E [0x]<engineID> EngineID used for Kul generation.
              <engineID>  is  intepreted as a hex string when preceeded by 0x,
              otherwise it is treated as a text string. If  no  <engineID>  is
              specified,  it  is constructed from the first IP address for the
              local host.

       -f     Force passphrases to be read from standard input.

       -h     Display the help message.

       -N "<new_passphrase>"
              Passphrase used to generate the new Ku.

       -O "<old_passphrase>"
              Passphrase used to generate the old Ku.

       -P     Turn off the prompt  for  passphrases  when  getting  data  from
              standard input.

       -v     Be verbose.

       -V     Echo passphrases to terminal.


       The  localized key method is defined in RFC 2274, Sections 2.6 and A.2,
       and originally documented in

              U. Blumenthal, N.  C.  Hien,  B.  Wijnen,  "Key  Derivation  for
              Network   Management   Applications",   IEEE  Network  Magazine,
              April/May issue, 1997.