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macutil(1)		      Mail Avenger 0.8.4		    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 0.8.4		  2013-07-13			    macutil(1)

NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT | FILES | SEE ALSO | BUGS | AUTHOR

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