CD-ROM Magic 1995 #1/CDM_5.ISO/shell/mailers/im/imcrypt.arj/IMCRYPT.DOC

Text File | 1993-12-27 | 14.3 KB | 347 lines

                        ImCrypt v 0.2 alfa

Overview
========

ImCrypt is a utility for MS-DOS platforms to facilitate sending and
receiving PGP encrypted messages via FidoNet (tm) style e-mail.

What it basicly does is scanning the netmail directory for message addressed
to one of your users at one of your AKA's, separating the message text from
the headers and the kludges in messages, running PGP to encrypt or decrypt
the message text and making new messages from the old headers and kludges
and the modified text.

ImCrypt is tuned for InterMail 2.2 or higher. For this pre-release version
that means it will ONLY work in the InterMail environment. The final
release version may or may not have provisions to work in other environ-
ments that use a *.msg netmail base.

IMCRYPT ?  will give a short help screen.


Copyright notice
----------------

ImCrypt may be freely distributed by any means provided that all the files
are distributed as a package and unchanged. No distribution fee may be im-
posed, other then the immidiate cost involved in the distribution itself.
Repacking to another compressed format is allowed. Adding a BBS header is
no problem. Distributing packages with other modifications is not allowed.

Noncommercial use within fidonet or a fidonet-like environment is free. For
commercial use, please contact the author.


The distrubution package
========================

The distribution package contains the .EXE file, the documentation
and the C source file. The main purpose of distributing the source file is
to enable interested partys to verify for themselves that no dirty tricks
have been build in to compromise the security offered by PGP. You may use
it for any other legal non-commercial purpose if you like, but you may not
distribute modified versions of the source without the authors permission.
Additional information may be found in the READ.ME file.


The environment
===============

ImCrypt takes most of the parameters needed from the InterMail configuration
file FD.SYS. In order to do this, it must be able to find this file.
The environment variable "IM" must be set to do this. When ImCrypt is run
from the main InterMail batch file, this will be no problem. When run from
the command line, the user must ensure that the "IM" environment variable
points to the directory where FD.SYS can be found. This can be done with
de DOS SET command.

Due to the extensive use of environment variables, it may be nessecary to
increease the environment spave with the DOSS SHELL command.

ImCrypt will find the netmail directory, the semaphore directory, your
AKA's and your user names from FD.SYS.

As explained in the overview, ImCrypt calls PGP.EXE if it needs to encrypt
or decrypt messages. To do this, it must be able to locate PGP.EXE, the
public and secret key rings and the PGP pass frase. For an explanation
of these, see the documentation of PGP.

There are five ways of letting ImCrypt know where to find PGP.EXE.

1) See that PGP.EXE is in the current directory.

2) Let the environment variable "PGPPATH" (without qoutes) point to it.

3) Have the DOS PATH point to it.

4) Enter the path to PGP.EXE in the config file IMCRYPT.CFG.

5) Enter the path tot PGP.EXE with the "p" option on the command line.

If more than one of these options is active at the same time, the one
later mentioned in this list has higher priority. The second method can
only be used if PGP.EXE and the keyrings are in the same directory.

More about the IMCRYPT.CFG file and command line options later.


For PGP to work, it must be able to locate the keyrings. Therefore the
environment variable "PGPPATH" must be properly set. Note that ImCrypt
itself does nothing with with this variable except use is as a last resort
to locate PGP.EXE if it can't find it anywhere else.

The third thing that may be needed is the PGP pass frase. One way to do
it, is to set the "PGPPASS" environment variable. Please read the relevant
section in the PGP documentation. This method has its risks. These risks are
explained in the PGP doc, much better than I could do it. Be sure to be
aware of the risks of this method before using it.

An other way to do it, is to use the "-b" option on the command line or
in IMCRYPT.CFG. PGP will then be called in interactive mode and will prompt
for pass frase if needed. Be sure to be present at the keyboard if you use
this mode.


The semaphores
==============

Imcrypt will touch the semaphore files IERESCAN.NOW and IMRESCAN.NOW
whenever it has changed one ore more messages in the netmail directory.
It will also prevent another program from changing something in the netmail
directory by handling the IMRENUM.NOW semaphore if it detects that is
not running in a single task environment.

The algorithm for detecting a multitask environment is as follows: first
it will check if SHARE is loaded. If so, it will assume a multitask envi-
ronment. If not, it will check if a network is perhaps present. It will
check for the precense of MICROSOFT network, Lantastic, Starlan extended
netbios or IPX. If either of these is active, a network is assumed if
the semaphores are on drive F or higher. Note that the OS2 DOS box will
trick ImCrypt into thinking SHARE is loaded.

If neither of these conditions is met, a single task environment is assumed
and the IMRENUM.NOW semaphore is not used.

Checking for a multitasking environment is nessesary, because of the
peculiar way InterMail handles the IMRENUM.NOW semaphore. It depends on
waiting for a lock to be established on a part of the file. In case of
a single tasking environment, a lock can never be obtained, so it would
wait forever. Unfortunatly there is no obvious way to tell if a lock has
failed because a file is not sharable or because it is busy.

The automatic detection of a multitasking environment can be overridden
with the "s" command line option. The detection mechanism is not perfect
and may fail in some cases. "-s" tells IMCRYPT to always ignore IMRENUM.NOW
and "+s" tells it to involve the locking mechanism always.


Logging
=======

Imcrypt provides for logging. The logging mechanism is invoked with the
"l" option on the command line or in the config file.
A single "l" will use IMCRYPT.LOG in the current directory. A full name
and path may be specified with "l=filespec". A minus sign before the "l"
will overwrite the log each time ImCrypt is called, otherwise it will
append new information to the end of an existing file. "l=*" will write
the log information to the mailer #1 logfile. Use this only if ImCrypt
is never called when mailer #1 is online or else a sharing violation
may result.


How does it work
================

ImCrypt scans the netmail directory for messages from you and for messages
to you. A message is considered from you if its "from field" contains one
of the names listed in FD.SYS and originates from one of your AKA's
listed in FD.SYS. When comparing the names, case is ignored. If it finds
such a message, and it is not yet marked as "send", it will scan the
message for one of the following first lines:

PGP ENCRYPT
PGP SIGN ENCRYPT
PGP SIGN
PGP CLEARSIG

The line may be hidden with an ^A kludge character. In that case, it
need not be the first line. As far as I know there is no editor that can
do this, but it does no harm to be prepaired.
If it finds one of these, it will extract the message text and write it
to a temporary file. It will then call PGP with this temporary file as input
and will let PGP do the obvious thing. The output of PGP will be  used
to build a new message with the original headers and kludges and the modified
message text. The line "PGP xxx" or the PGP kludge that triggered the
process is not written to the new message. Instead a naked ^APGP kludge is
written to the new message.

The original message will be marked as "send". The new message will get
the "kill-send" status, so that it will be removed by the mailer after it
is send.


If ImCrypt finds a message addressed to you, that does not have the
in transit flag set, it will scan the message for the characteristic
PGP header of five dashes and the words "BEGIN PGP". If it finds these,
it will extract the message text, write it to a temp file and call PGP
with this temp file as input to decrypt the text.

Depending on the "k" option, as explained later, it will replace the
text in the original message or  build a new message. A "PGP" kludge in
the message will be removed. In case the original message is retained it will
replace the first of the five dashes in the PGP header with an asterisk, so
that it does not recognise this message as crypted during subsequent passes.

ImCrypt was intended for use in the batch. Call it whenever new messages to
you may have landed in your netmail directory, so whenever the mailer
exits with mail received status or the tosser has finished unpacking
the netmail. Call it also before letting your tosser pack the netmail or
before sending mail to your up- or downlinks.

If you think this is unsafe (and unless you run an end user system, you
have good reason to think so), you may also call ImCrypt from the DOS
command line or from your favorite editor if your editor allows you to
that. In that case set the PGPPASS environment variable by hand or use
the -B option to disable batch mode.


Options
=======

The operation of ImCrypt is controled by option switches.

An option is a single letter, optionally prefixed with a
slash '/', optionally followed by a string parameter. The letter and the
string parameter may optionally be separated by a semicolon or an equals
sign. Both upper and lower case is allowed.

A minus sign before the option is sometimes used to negate or modify an
option. In other case a minus sign is ignored.

The option 'l' can be written in the following variants.

 lFILENAME.EXT
 l=FILENAME.EXT
 /l:FILENAME.EXT
 /l=FILENAME.EXT
 -l

Filenames may be specified with a full path. If a directory is specified
it need not be terminated with a backslash. ImCrypt adds it automatically
if left off.

Options are specified on the command line, separated by a single space
or in a file IMCRYPT.CFG in the current directory. A config file is a
plain ASCII text file. It must contain one option per line with no leading
or trailing spaces. Comment lines starting with a semicolon are allowed.
A config file is not mandatory, but if it exists it is read before the
command line is parsed. Therefore options on the command line will
override options in the config file.


The options in alfabetical order:

 -B  Disable batch mode. PGP is called in interactive mode and will prompt
     for the pass frase or other information if needed. Do not use this
     in unattended operation.

 -D  Skip the  decryption fase.

 -E  Skip the encryption fase

  K  Keep encrypted messages addressed to you. The decrypted content of
     the message is written to a new message. Without this option no new
     message is created, the old message is overwritten with the decrypted
     text. Use of this parameter is recommended in the debug fase.

  L  Enable logging. A single "L" will use IMCRYPT.LOG in the current
     directory. A path and filename may be specified with l=<filespec>.
     An asterisk for the filespec will use the #1 mailers log file. Be
     carefull with this option in a multitasker or network environment.
     Placing a minus sign in front of the "L" will cause the logfile to
     be overwritten at each call of ImCrypt. Otherwise the logfile keeps
     on growing.

  P  Specify a path for PGP.EXE. If PGP.EXE is not in the DOS path, this
     tells ImCrypt where to find it. If this option is not used and
     PGP is not found in the DOS path, ImCrypt will look for PGP.EXE
     in the same directory as where the keys are located. The location
     of the keys must be in the PGPPATH environment variable. If all of
     this fails, the current directory will be searched for PGP.EXE.

  S  Overrides the autodetect of a multitasker or network. +S tells
     ImCrypt to use the IMRENUM.NOW semaphore always, even if it finds
     that it may not be sharable. -S tells it to never use it, even if
     it  finds that it is sharable.

  T  Specify a directory for temporary files. Both ImCrypt and PGP make
     use of temporary files. An alternative way to specify a temp direc-
     tory is the environment variable TMP. By default ImCrypt will use
     the semaphore directory as found in FD.SYS. Use of a ramdisk for the
     temp. directory is recommended.

  V  Set verbosity. Valid parameters are V=0, V=1 and V=2. This provides
     for extra information, mainly usefull for debugging purposes. Default
     setting is V=0.



ImCrypt v0.2 is written in Turbo C and compiled with the tiny model.
It is tested on 286 AT and 386 clones using MS DOS 5.0 and under NOVELL 3.11
Because it does not use any fancy DOS or BIOS calls, there is no reason
to suspect it should not work with anything above MS DOS 3.2 or any
future versions of MS-DOS. However... no guarantee.

It was tested with InterMail 2.10 and 2.25. There is no reason it should
not work for any 2.x version. Ad regard to future versions; if the basic
structure of the FD.SYS file remains upward compatible, it will most
likely continue to function.

This version was tested with PGP v2.3a. Compatibilty with future versions
is not guaranteed.


DISCLAIMER
==========

Although all reasonable effort is made to avoid adverse side effects,
the author accepts no responsibility whatsoever for any alleged damages
resulting from the use of this program. It is not guaranteed to do any-
thing else than take up disc space.


Acknowledgements
================

FidoNet is a trademark by Tom Jennings

InterMail is a trademark by Scandinavian PC Sytems AB and InterZone
SoftWare Inc.

MS-DOS, OS/2 and Windows are trademarks of the Microsoft corporation.

Lantastic is a trademark of Artisoft corporation.

IPX is a product of Novell inc.

PGP (Pretty Good Privacy) is copyrighted by Phillip Zimmermann.


=======

I would like to thank the following persons in no particular order for
making helpfull suggestions, pointing out bugs and spending time and
effort in testing:

Evert Bruinsma.

=====

Michiel van der Vlist (2:500/9.5)
Dec 1993