sshhaaddooww -- System Administration

File that holds restricted passwords
/eettcc/sshhaaddooww

COHERENT stores information  in file /eettcc/ppaasssswwdd. This file identifies each
user, gives her home directory, default  shell, and base group.  It must be
universally readable so that it can be used by programs like llss, which must
translate user-identification numbers into login identifiers.

In  general, this  system works  well; however,  it does  create a  hole in
system security.   If users' encrypted  passwords are kept  in /eettcc/ppaasssswwdd,
which  is  universally  readable, a  ``cracker''  can  read the  passwords,
decypher some  of them  with brute-force  methods, and then  log in  as the
users whose passwords she cracked.

To  plug that  hole  in system  security,  UNIX implemented  the method  of
``shadow'' passwords.  In this  scheme, a user's login information is still
kept in  /eettcc/ppaasssswwdd; however,  the encrypted passwords  (plus supplemental
information) is kept  in the file /eettcc/sshhaaddooww, which can  be read only by a
process with root-level permissions.

The shadow password file contains one entry per user.  Each user identified
in /eettcc/sshhaaddooww must have an entry in /eettcc/ppaasssswwdd. The opposite is not true,
but  a  user  described in  /eettcc/ppaasssswwdd  who  does  not  have an  entry  in
/eettcc/sshhaaddooww cannot log into your system.  Each entry in /eettcc/sshhaaddooww is laid
out  exactly  the  same  as  file  /eettcc/ppaasssswwdd. At  present,  the  COHERENT
implementation  of  llooggiinn uses  only  the _n_a_m_e  and  _p_a_s_s_w_o_r_d fields.   For
details, see the Lexicon entry for ppaasssswwdd.

_S_e_e _A_l_s_o
AAddmmiinniisstteerriinngg CCOOHHEERREENNTT, llooggiinn

_N_o_t_e_s
For details of  how the program llooggiinn uses shadow  passwords, see its entry
in the Lexicon.
