Provided by: otpw-bin_1.5-2_amd64 bug


       otpw-gen - one-time password generator


       otpw-gen [ options ]


       OTPW  is a one-time password authentication system. It can be plugged into any application
       that needs to authenticate users interactively.  One-time  password  authentication  is  a
       valuable  protection  against password eavesdropping, especially for logins from untrusted

       Before you can use OTPW to log into your system,  two  preparation  steps  are  necessary.
       Firstly,  your system administrator has to enable it. (This is usually done by configuring
       your login software (e.g., sshd) to use OTPW via the Pluggable Authentication Module (PAM)
       configuration files in /etc/pam.d/.)

       Secondly,  you need to generate a list of one-time passwords and print it out. This can be
       done by calling

              otpw-gen | lpr

       or something like

              otpw-gen -h 70 -s 2 | a2ps -1B -L 70 --borders no

       if more control over the layout is desired.

       You will be asked for a prefix password, which you need to memorize. It has to be  entered
       immediately before the one-time password. The prefix password reduces the risk that anyone
       who finds or steals your password printout can use that alone to impersonate you.

       Each one-time password will be printed behind a three digit password number. Such a number
       will appear in the password prompt when OTPW has been activated:

              Password 026:

       When you see this prompt, enter the memorized prefix password, followed immediately by the
       one-time password identified by the number. Any spaces within a password  have  only  been
       inserted  to  improve  legibility  and  do  not  have  to be copied.  OTPW will ignore the
       difference between the easily confused characters 0O and Il1 in passwords.

       In some situations, for example if multiple logins occur simultaneously for the same user,
       OTPW  defends itself against the possibility of various attacks by asking for three random
       passwords simultaneously.

              Password 047/192/210:

       You then have to enter the prefix password, followed immediately by  the  three  requested
       one-time  passwords.  This  fall-back  mode is activated by the existence of the lock file
       ~/.otpw.lock.  If it was left over by some malfunction, it can safely be deleted  manually
       using option -l.

       Call  otpw-gen again when you have used up about half of the printed one-time passwords or
       when you have lost your password sheet. This will disable all remaining passwords  on  the
       previous sheet.


       -h number     Specify  the  total  number of lines per page to be sent to standard output.
                     This number minus four  header  lines  determines  the  number  of  rows  of
                     passwords  on each page. The maximum number of passwords that can be printed
                     is 1000. (Minimum: 5, default: 60)

       -w number     Specify the maximum width of lines to  be  sent  to  standard  output.  This
                     parameter determines together with the password length the number of columns
                     in the printed password matrix. (Minimum: 64, default: 79)

       -s number     Specify the number of form-feed separated  pages  to  be  sent  to  standard
                     output. (Default: 1)

       -e number     Specify the minimum entropy of each one-time password in bits. The length of
                     each password will be chosen automatically, such that there are at least two
                     to  the  power  of the specified number possible passwords. A value below 30
                     might make the passwords vulnerable to a brute-force guessing attack. If the
                     attacker  might have read access to the ~/.otpw file, the value should be at
                     least 48. Paranoid users might prefer long high-security passwords  with  at
                     least 60 bits of entropy.  (Default: 48)

       -p0           Generate  passwords  by  transforming a random bit string into a sequence of
                     letters and digits, using a form of base-64 encoding (6 bits per character).

       -p1           Generate  passwords  by  transforming a random bit string into a sequence of
                     English four-letter words, each chosen from a fixed list of 2048 words (2.75
                     bits per character).

       -p2           Generate  passwords  by  transforming a random bit string into a sequence of
                     lowercase letters and digits (5 bits per character).  These  are  easier  to
                     communicate by voice (e.g., using the NATO alphabet).

       -f filename   Specify  a file to be used instead of ~/.otpw for storing the hash values of
                     the generated one-time passwords.

       -n            Suppress the addition of a header and footer line to each output page.  This
                     reduces the minimum value for option -h to 1.

       -m            Instead  of  generating each password randomly, generate a random master key
                     and then derive each password from that in a deterministic way.  The  master
                     key  will  be printed to standard error. It can later be used with option -k
                     to recreate another copy of the same one-time password list. (Each  password
                     is generated from the output of a secure hash function applied to the master
                     key and the challenge string.)

       -E number     Specify the minimum entropy of the master  key  in  bits.  (It  contains  in
                     addition four bits redundancy for error checking.)

       -P number     Choose  the  text  format  in  which  the master key will be displayed.  The
                     supported values are the same as with option -p.

       -k            Ask for a master key, as it was generated by option -m,  and  then  recreate
                     the  same  password  list  from that. With this option, only a password list
                     will be generated; the hash values in ~/.otpw remain unmodified.

       -r            Output a suggestion for a random password, then exit. The length and type of
                     password can be selected with options -e and -p.

       -l            Remove any lock file left by previous authentication attempts, then exit.


       If  the  otpw-gen  binary, owned by some system pseudo user (e.g., “otpw”), has the SETUID
       bit set, then the password hash file will be owned by and stored in the home directory  of
       that  pseudo  user (e.g., “/var/lib/otpw”), using the user's name instead of “.otpw”. This
       way, the hash files are out of reach from the users, and cannot be  manipulated  by  tools
       other than otpw-gen, which can help to enforce policies about how passwords are generated.
       Storing the password hash files outside the user's home directory can also be useful where
       the home directory may not yet be accessible during login.


       The  OTPW package, which includes the otpw-gen program, has been developed by Markus Kuhn.
       The most recent version is available from <>.


       pam(8), pam_otpw(8)

                                            2014-08-07                                OTPW-GEN(1)