macutil(1)                    Mail Avenger 0.8.1                    macutil(1)



NAME
       macutil, sendmac - Message Authentication Code utility

SYNOPSIS
       macutil --gen [options]

       macutil --sender [template] [--from name] [options]

       macutil --check [options] code

       macutil [options] --sendmail [sendmail-options]

       sendmac [sendmail-options]

DESCRIPTION
       macutil generates and checks the validity of codes that can be embedded
       in temporary email addresses.  The codes are calculated using a secret
       passphrase stored in a file.  Thus, someone who does not know the
       passphrase cannot easily generate a valid code.  Each code has a
       configurable expiration time after which it becomes invalid.

       To use macutil, you must create a file containing a passphrase.  The
       default location of this file is $HOME/.avenger/.macpass, though the
       location can be overridden with the MACUTIL_PASSFILE environment
       variable or --passfile= command-line option.  The file should contain a
       passphrase followed by a newline.  The maximum allowed length of the
       passphrase is 64 characters.  Do not use your Unix login password or
       any password you have used for a sensitive application, as macutil's
       password will be stored in cleartext and thus be relatively easy to
       compromise.

       Running macutil --gen generates a new code and writes it to standard
       output.

       Running macutil --check code checks the validity of code.  If the code
       is valid and has not expired, macutil exits with status 0.  If the code
       is invalid or has expired, macutil prints a message to standard error
       and exits with a non-zero exit code.

       The following options affect macutil's behavior:

       --gen (-g)
           Generates a code, as described above.

       --sender template (-s template)
           This option is like --gen, but outputs a complete email address,
           instead of just a code.  The address is formatted based on
           template.  template should contain an email address with a "*"
           character.  The "*" will be replaced by a code.  For example, if
           template is "myname+bounces+*", running "macutil --sender" might
           output:

               myname+bounces+zjkifk8kuvsy7rubu7vqadmwnn

           Don't forget to quote the "*" character when invoking macutil from
           a shell.

       --from name (-f name)
           This option, in conjunction with --sender, produces output more
           suitable for the "From:" field in an email message header.  For
           example, if name is set to "Mail Avenger", running "macutil
           --sender 'myname+tmp+*host' --from 'Mail Avenger'" might output:

               Mail Avenger <myname+tmp+zjkifk8kuvsy7rubu7vqadmwnn@host>

           Note that if the MACUTIL_SENDER environment variable has been set,
           this will be used as a default vaule for the --sender option if you
           invoke macutil --from and don't specify a --sender.

       --fromexp phrase
           In conjunction with the --from option, this option includes an
           expiration time for the address in a comment.  For example,
           supplying a phrase of "address expires" would result in output like
           this:

               Mail Avenger (address expires 07 Dec 2004)
                   <myname+tmp+zjkifk8kuvsy7rubu7vqadmwnn@host>

       --check (-c)
           Checks a code, as described above.  Exits 0 on success; exits non-
           zero with a message to standard error if the code is invalid.

       --passfile=file (-p file)
           Specify the passphrase file to use.

           Note that if file contains multiple passphrases, one per line,
           --gen always uses the first passphrase in the file.  --check,
           however, will try all passphrases until one succeeds, and only
           output failure if they all fail.  In this way, you can change your
           passphrase, but keep accepting the old one for a time by leaving it
           as the second line of the file.

       --expire=date
           Specify the expiration date for the code.  date can be an absolute
           number of seconds since midnight, Jan 1, 1970, GMT.  Alternatively
           (and perhaps more usefully), it can be expressed relative to the
           current time, as:

           +numh
           +numD
           +numW

           to specify num hours, days, or weeks in the future.  The full range
           of suffixes allowed is s, m, h, D, W, M, and Y, which designate
           seconds, minutes, hours, days, weeks, months, and years,
           respectively.  The default expiration time is 21 days ("+21D").

       --aux=string
           Permutes the algorithm using string.  You must specify the same
           --aux argument when both generating and checking codes.  This
           allows you to re-use the same password for different sets of codes.
           For example, you might require tokens generated with "macutil --gen
           --aux=list1" to be embedded in recipient addresses for one mailing
           list, and "macutil --gen --aux=list2" to be embedded in recipient
           addresses for another.  Someone who has an address that is valid
           for one list will still not be able to send to the other.

       --date=date
           Run as if the current time were date.  As with --expire, date can
           be an absolute number or can be relative to the current time.  Use
           - instead of + to specify a time in the past (e.g., -numh or
           -numD).

       --sendmail
           This option must be the last sendmac option.  It tells macutil to
           run sendmail with the remaining arguments you have specified, but
           to insert the options -f address at the beginning of the argument
           list, where address is generated as with the --sender option.  You
           must specify an address template, either through explicit use of
           the --sender option, or by setting the MACUTIL_SENDER environment
           variable.

           For example, if MACUTIL_SENDER is "myname+bounces+*", running
           "macutil --sendmail friend@domain.com" might run the command:

               sendmail -f \
                   myname+bounces+zjkifk8kuvsy7rubu7vqadmwnn \
                   friend@domain.com

           Note that if invoke the macutil program as "sendmac" (or as any
           other name you link it to beginning with the four letters "send"),
           it will automatically behave as though there were an extra first
           argument of --sendmail.  (In this case, you cannot specify any
           sendmac options, but you can still control sendmac's behavior
           through the environment variables listed below.)

ENVIRONMENT
       MACUTIL_EXPIRE
           Sets the expiration time if not explicitly overwritten by the
           --expire flag.  If MACUTIL_EXPIRE is not set, macutil uses a
           default value of "+21D" (21 days).

       MACUTIL_FROMEXP
           If this option is set to phrase, then the output of "sendmac
           --from" will always behave as though an extra --fromexp phrase
           argument had been supplied.

       MACUTIL_PASSFILE
           Specifies a passphrase file other than the default of
           $HOME/.avenger/.macpass.

       MACUTIL_SENDER
           Specifies a template sender address to use as a default value of
           --sender with the --sendmail and --from options.  See the
           descriptions of the --sendmail and --from options above for more
           information.

       MACUTIL_SENDMAIL
           Specifies the path to sendmail for the --sendmail option.  The
           default is just sendmail.

FILES
       $HOME/.avenger/.macpass

SEE ALSO
       avenger(1)

       The Mail Avenger home page: <http://www.mailavenger.org/>.

BUGS
       macutil is designed to provide casual security against people trying to
       guess a valid temporary email address.  Don't use it where stronger
       authentication is required.  In particular, for any given passphrase, a
       random code will be valid (at least on some date) with probability 1 in
       2^64.  While these are tough odds to beat, cryptographers generally
       prefer a margin of safety closer to 1 in 2^128 for high-security
       applications (though that would require longer codes).

       Someone who sees a valid code can mount an off-line dictionary attack
       against your passphrase.  In other words, while it is hard recover your
       passphrase outright, given a valid code, it is is easy to verify
       whether a particular guess of your passphrase is correct.  By guessing
       every word in the dictionary, an attacker can recover weak passphrases.

       Technically, the cryptographic operation performed on the keys is
       encryption, not a message authentication code (or MAC).  Hence, one
       could argue the utility is misnamed.

AUTHOR
       David Mazieres



Mail Avenger 0.8.1                2010-04-12                        macutil(1)
