PMDF System Manager's Guide
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25.2.3 Examples on UNIX

The following sections provide examples of using BSMTP channels on UNIX.

25.2.3.1 Configuring the BSMTP Channels to Compress Their Payloads on UNIX

Using PMDF's general purpose, on-the-fly conversion facilities, BSMTP parcels can be compressed on the sending system and then uncompressed on the receiving system. This allows for faster transmission of the parcels through the network.

In the CHARSET-CONVERSION mapping table on each PMDF system, a simple entry enabling conversions for the BSMTP channels must be made: 


CHARSET-CONVERSION 
 
  in-chan=bsout_*;out-chan=*;convert      yes 
  in-chan=*;out-chan=bsin_*;convert       yes

In the PMDF conversions file on each system, conversion entries are added which call out to the site-supplied shell script, compress.sh: 


in-chan=bsout_*; part-number=1; in-type=*; in-subtype=*; 
  service-command="/pmdf/bin/compress.sh compress $INPUT_FILE $OUTPUT_FILE" 
 
out-chan=bsin_*; part-number=1; in-type=application; 
  in-subtype=compressed-bsmtp; 
  service-command="/pmdf/bin/compress.sh decompress $INPUT_FILE $OUTPUT_FILE"
The compress.sh shell script is shown in Figure 25-4. It assumes that the gzip and gunzip utilities are installed in /usr/local/bin/.

Figure 25-4 compress.sh : Compress and decompress BSMTP payloads 


#!/sbin/sh 
 
# compress operation in-file out-file [addr-file] 
 
# where 
 
#   operation   == "compress" | "decompress" 
#   input-file  == path of file to sign or verify 
#   output-file == output file to produce 
#   addr-file   == file of envelope recipient addresses 
 
if [ $# -lt 3 ]; then exit 1; fi 
 
case $1 
in 
  compress ) 
        /usr/local/bin/gzip < $2 > $3.tmp 
        /pmdf/bin/pmdf encode -nofilename -encoding=base64 -type=application \
                -subtype=compressed-bsmtp $3.tmp $3.tmp2 
        rm -f $3.tmp $3.tmp2 
        ;; 
 
  decompress ) 
        /pmdf/bin/pmdf decode $2 $3.tmp 
        /usr/local/bin/gunzip < $3.tmp > $3 
        rm -f $3.tmp 
        ;; 
 
  * ) 
        exit 1 
        ;; 
esac 
exit 0

25.2.3.2 Configuring the BSMTP Channels to Provide Authentication Services on UNIX

Using PMDF's general purpose, on-the-fly conversion facilities, authentication and integrity services may be tied in to the BSMTP channels. This is done through the CHARSET-CONVERSION mapping table, the PMDF conversions file, and a site-supplied shell script to digitally sign payloads and verify the signature and integrity of the data upon receipt.

In the CHARSET-CONVERSION mapping table on each PMDF system, a simple entry enabling conversions for the BSMTP channels must be made: 


CHARSET-CONVERSION 
 
  in-chan=bsout_*;out-chan=*;convert      yes 
  in-chan=*;out-chan=bsin_*;convert       yes

In the PMDF conversions file file on each system, there must be conversion entries to invoke the site-supplied shell scripts: 


in-chan=bsout_*; part-number=1; in-type=*; in-subtype=*; 
  service-command="/pmdf/bin/pgp_sign.sh $INPUT_FILE $OUTPUT_FILE" 
 
out-chan=bsin_*; part-number=1; in-type=multipart; in-subtype=signed; 
  service-command="/pmdf/bin/pgp_verify.sh $INPUT_FILE $OUTPUT_FILE"
These two scripts are shown in Figures 25-5 and 25-6. They assume that the pgp utility is installed in /usr/local/bin/ and that awk is installed in /usr/bin/. Note that the pgp_sign.sh script requires the pass phrase for the PMDF MTA's private PGP key in order to generate signatures. Edit the script to reflect the correct pass phrase and be sure to protect the file from other users: 


% chown pmdf:bin /pmdf/bin/pgp_sign.sh
% chmod 0700 /pmdf/bin/pgp_sign.sh

Figure 25-5 pgp_sign.sh : Digitally sign BSMTP payloads 


#!/sbin/sh 
 
# pgp_sign.sh input-file output-file [addr-file] 
 
# where 
 
#   input-file  == path of file to sign or verify 
#   output-file == output file to produce 
#   addr-file   == file of envelope recipient addresses 
 
# Check that we have at least three command line parameters 
if [ $# -lt 2 ]; then exit 1; fi 
 
# Change these to match your site 
PGPUSER="PMDF MTA key" 
PGPPATH=/pmdf/table/pgp 
PGPPASS="Percy eats pealed banannas" 
 
# Generate the digital signature 
/usr/local/bin/pgp -sab $1 -u $PGPUSER -z $PGPPASS -o $2 +batchmode 
 
# Make some temporary files used to MIME-ify the results 
BOUNDARY=`/pmdf/bin/unique_id` 
echo 'Content-type: multipart/signed; boundary="'$BOUNDARY'"; '\
'micalg=pgp-md5; protocol=application/pgp-signature 
 
--'$BOUNDARY > $2.top 
echo '--'$BOUNDARY' 
Content-type: application/pgp-signature 
' > $2.mid 
echo --$BOUNDARY-- > $2.bot 
 
# Make a multipart/signed message part 
cat $2.top $1 $2.mid $2.asc $2.bot > $2 
 
# Now clean up 
rm -f $2.top $2.mid $2.asc $2.bot 
 
# And exit 
exit 0

Figure 25-6 pgp_verify.sh : Verify the integrity of a digitally signed BSMTP payload 


#!/sbin/sh 
 
# pgp_verify.sh input-file output-file [addr-file] 
 
# where 
 
#   input-file  == path of file to sign or verify 
#   output-file == output file to produce 
#   addr-file   == file of envelope recipient addresses 
 
# Check that we have at least three command line parameters 
if [ $# -lt 2 ]; then exit 1; fi 
 
# Change this to match your site 
PGPPATH=/pmdf/table/pgp 
 
# Use awk to split the multipart/signed part into 
# two files: the signed data and the digital signature 
/usr/bin/awk ' 
BEGIN { state = 0 } 
{ 
        if (state == 0) { 
                if (substr ($0, 0, 2) == "--") { 
                        boundary = $0 
                        state = 1 
                } 
        } else if (state == 1) { 
                if ($0 != boundary) { 
                        print $0 > OUT_DATA 
                } else { 
                        state = 2 
                } 
        } else if (state == 2) { 
                if (NF == 0) state = 3 
        } else if (state == 3) { 
                print $0 > OUT_SIGN 
        } 
}' OUT_DATA=$2.data OUT_SIGN=$2.sign $1 
 
# Verify the digital signature 
/usr/local/bin/pgp $2.sign $2.data +batchmode > $2.check 
 
# Build a X-Content-MIC-check: header line 
MICINFO=`grep -h ' signature from user ' $2.check` 
if [ -n "$MICINFO" ] 
then 
        echo 'X-Content-MIC-check: '$MICINFO > $2.mic 
else 
        echo 'X-Content-MIC-check: Bad signature' > $2.mic 
fi 
cat $2.mic $2.data > $2 
 
# Clean up 
rm -f $2.sign $2.data $2.check $2.mic 
 
# And exit 
exit 0

25.2.3.2.1 Using PGP with PMDF on UNIX

Note
Use of PGP for commercial purposes requires a license from Pretty Good Privacy, Inc. Please contact Pretty Good Privacy, Inc. for details and assistance in licensing PGP.

Use of PGP requires installation of PGP as well as generation and exchange of PGP public keys between the PMDF BSMTP systems which will be using PGP for authentication. This section documents step-by-step how to generate and exchange PGP keys. No attempt is here made to document PGP. Please refer to the documentation supplied with PGP for information on those subjects.

  1. Acquire copies of PGP and install it on the PMDF systems. The following URLs might be helpful: 


     
<http://www.pgp.com/> 
<ftp://ftp.csn.net/mpj/getpgp.asc> 
<http://world.std.com/~franl/pgp/where-to-get-pgp.html>

  2. After installing PGP, create an MTA key for the PMDF system. Note that the name for the key will be 


    PMDF MTA key bsmtp@bsin.host0
    bsmtp@bsin.host0 where host0 is as in Section 25.1. The important element here is that the remote BSMTP channel will send the message to the address bsmtp@bsin.host0. The local PMDF system will receive that message and, via the FORWARD mapping table, route it to the incoming BSMTP channel, bsin_gateway, for the recipient bsmtp@bsin.host0. This recipient address is the user id of the decryption key which will be used. The PGP key rings need to be located somewhere; placing them in the directory /pmdf/table/pgp is as good as place as any. The easiest way to set this up is as follows: 


    % su pmdf
% cd /pmdf/table
% mkdir pgp
% setenv PGPPATH /pmdf/table/pgp
% pgp -kg
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses. 
(c) 1990-1994 Philip Zimmermann, Phil's Pretty Good Software. 11 Oct 94 
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc. 
Distributed by the Massachusetts Institute of Technology. 
Export of this software may be restricted by the U.S. government. 
Current time: 1997/04/02 20:44 GMT 
Pick your RSA key size: 
    1)   512 bits- Low commercial grade, fast but less secure 
    2)   768 bits- High commercial grade, medium speed, good security 
    3)  1024 bits- "Military" grade, slow, highest security 
Choose 1, 2, or 3, or enter desired number of bits: 3
Generating an RSA key with a 1024-bit modulus. 
 
You need a user ID for your public key.  The desired form for this 
user ID is your name, followed by your E-mail address enclosed in 
<angle brackets>, if you have an E-mail address. 
For example:  John Q. Smith <12345.6789@compuserve.com> 
Enter a user ID for your public key: PMDF MTA key <bsmtp@bsin.host0>
 
You need a pass phrase to protect your RSA secret key. 
Your pass phrase can be any sentence or phrase and may have many 
words, spaces, punctuation, or any other printable characters. 
 
Enter pass phrase: secret
Enter same pass phrase again:  secret
Note that key generation is a lengthy process. 
 
We need to generate 736 random bits.  This is done by measuring the 
time intervals between your keystrokes.  Please enter some random text 
on your keyboard until you hear the beep: 
   0 * -Enough, thank you. 
....**** ..............****
Key generation completed. 
% ls -l pgp
total 6 
-rw-------   1 pmdf     30           197 Apr  2 12:52 pubring.pgp 
-rw-------   1 pmdf     30           408 Apr  2 12:52 randseed.bin 
-rw-------   1 pmdf     30           530 Apr  2 12:52 secring.pgp
    The final ls command verifies that the correct three PGP files have been created with appropriate rights.

  3. You may want change the permissions of the file pubring.pgp so that others can read the public key: 


    % chmod 644 pgp/pubring.pgp
% ls -l pgp
total 6 
-rw-r--r--   1 pmdf     30           197 Apr  2 12:52 pubring.pgp 
-rw-------   1 pmdf     30           408 Apr  2 12:52 randseed.bin 
-rw-------   1 pmdf     30           530 Apr  2 12:52 secring.pgp

  4. Now you need to sign your public key. This prevents someone else from modifying the user id of the key. 


    % pgp -ks bsmtp@bsin.host0
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses. 
(c) 1990-1994 Philip Zimmermann, Phil's Pretty Good Software. 11 Oct 94 
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc. 
Distributed by the Massachusetts Institute of Technology. 
Export of this software may be restricted by the U.S. government. 
Current time: 1997/04/02 20:46 GMT 
 
A secret key is required to make a signature. 
You specified no user ID to select your secret key, 
so the default user ID and key will be the most recently 
added key on your secret keyring. 
 
Looking for key for user 'bsmtp@bsin.host0': 
 
Key for user ID: PMDF MTA key <bsmtp@bsin.host0> 
1024-bit key, Key ID BFFA43E9, created 1997/04/02 
          Key fingerprint =  2F 5C A1 0A 35 25 E1 23  ED AF 23 11 00 37 5A CD 
 
READ CAREFULLY:  Based on your own direct first-hand knowledge, are 
you absolutely certain that you are prepared to solemnly certify that 
the above public key actually belongs to the user specified by the 
above user ID (y/N)? y
 
You need a pass phrase to unlock your RSA secret key. 
Key for user ID "PMDF MTA key <bsmtp@bsin.host0>" 
 
Enter pass phrase: secret
Pass phrase is good.  Just a moment.... 
Key signature certificate added.

  5. Repeat Steps (1)---(4) on the other PMDF systems.
  6. Next, you need to exchange public keys between the PMDF systems. On a given system, you may extract the public key as follows: 


    % pgp -kxa bsmtp@bsin.host0 extract
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses. 
(c) 1990-1994 Philip Zimmermann, Phil's Pretty Good Software. 11 Oct 94 
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc. 
Distributed by the Massachusetts Institute of Technology. 
Export of this software may be restricted by the U.S. government. 
Current time: 1997/04/02 20:47 GMT 
 
Extracting from key ring: '/pmdf/table/.pgp/pubring.pgp', 
  userid "bsmtp@bsin.host0". 
 
Key for user ID: PMDF MTA key <bsmtp@bsin.host0> 
1024-bit key, Key ID BFFA43E9, created 1997/04/02 
 
Transport armor file: extract.asc 
Key extracted to file 'extract.asc'.
    The file extract.asc may then be transferred by FTP or e-mail to the other PMDF system. If you're exchanging keys with another server you control go on to the next step. However, if you're exchanging keys with a remote site, some care needs to be taken to make sure the public keys are properly certified.

  7. The best way to exchange keys is to first exchange the key fingerprints via a reliable channel (e.g., face-to-face in person, or perhaps over a trusted phone line). The fingerprint can be obtained with the following command: 


    % pgp -kvc bsmtp@bsin.host0
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses. 
(c) 1990-1994 Philip Zimmermann, Phil's Pretty Good Software. 11 Oct 94 
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc. 
Distributed by the Massachusetts Institute of Technology. 
Export of this software may be restricted by the U.S. government. 
Current time: 1997/04/02 23:08 GMT 
 
Key ring: '/pmdf/table/.pgp/pubring.pgp', looking for user ID 
  "bsmtp@bsin.host0". 
Type bits/keyID    Date       User ID 
pub  1024/BFFA43E9 1997/04/02 PMDF MTA key <bsmtp@bsin.host0> 
          Key fingerprint =  2F 5C A1 0A 35 25 E1 23  ED AF 23 11 00 37 5A CD 
1 matching key found.
    Then the public key itself can be extracted as described in Step (6) and sent through e-mail. Upon receipt, the fingerprint should be manually verified before certifying the key. After adding and certifying the key for the remote server, you may want to sign that key as well. If you sign the key, and extract it as described in Step (6) this can be used to tell other people you believe that key actually belongs to the MTA it claims to belong to. For more information, see the PGP documentation.

  8. Add the key in extract.asc to the keyrings on the other PMDF systems. If you are unsure about how to answer the questions, see the PGP User's Manual. 


    % pgp extract.asc
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses. 
(c) 1990-1994 Philip Zimmermann, Phil's Pretty Good Software. 11 Oct 94 
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc. 
Distributed by the Massachusetts Institute of Technology. 
Export of this software may be restricted by the U.S. government. 
Current time: 1997/04/02 21:09 GMT 
 
File contains key(s).  Contents follow... 
Key ring: 'extract.$00' 
Type bits/keyID    Date       User ID 
pub  1024/BFFA43E9 1997/04/02 PMDF MTA key <bsmtp@bsin.host0> 
sig       BFFA43E9             PMDF MTA key <bsmtp@bsin.host0> 
1 matching key found. 
 
Do you want to add this keyfile to keyring '/pmdf/table/.pgp/pubring.pgp' (y/N)? y
 
Looking for new keys... 
pub  1024/BFFA43E9 1997/04/02  PMDF MTA key <bsmtp@bsin.host0> 
 
Checking signatures... 
pub  1024/BFFA43E9 1997/04/02 PMDF MTA key <bsmtp@bsin.host0> 
sig!      BFFA43E9 1997/04/02  PMDF MTA key <bsmtp@bsin.host0> 
 
Keyfile contains: 
   1 new key(s) 
 
One or more of the new keys are not fully certified. 
Do you want to certify any of these keys yourself (y/N)? y
 
Key for user ID: PMDF MTA key <bsmtp@bsin.host0> 
1024-bit key, Key ID BFFA43E9, created 1997/04/02 
Key fingerprint =  2F 5C A1 0A 35 25 E1 23  ED AF 23 11 00 37 5A CD 
This key/userID association is not certified. 
  Questionable certification from: 
  PMDF MTA key <bsmtp@bsin.host0> 
 
Do you want to certify this key yourself (y/N)? y
 
Looking for key for user 'PMDF MTA key <bsmtp@bsin.host0>': 
 
Key for user ID: PMDF MTA key <bsmtp@bsin.host0> 
1024-bit key, Key ID BFFA43E9, created 1997/04/02 
          Key fingerprint =  2F 5C A1 0A 35 25 E1 23  ED AF 23 11 00 37 5A CD 
 
 READ CAREFULLY:  Based on your own direct first-hand knowledge, are 
you absolutely certain that you are prepared to solemnly certify that 
the above public key actually belongs to the user specified by the 
above user ID (y/N)? y
 
You need a pass phrase to unlock your RSA secret key. 
Key for user ID "PMDF MTA key <bsmtp@bsin.host1>" 
 
Enter pass phrase: another-secret
Pass phrase is good.  Just a moment.... 
Key signature certificate added. 
 
Make a determination in your own mind whether this key actually 
belongs to the person whom you think it belongs to, based on available 
evidence.  If you think it does, then based on your estimate of 
that person's integrity and competence in key management, answer 
the following question: 
 
Would you trust "PMDF MTA key <bsmtp@bsin.host0>" 
to act as an introducer and certify other people's public keys to you? 
(1=I don't know. 2=No. 3=Usually. 4=Yes, always.) ? 2

  9. Repeat Steps (6)---(8) in the other direction.
  10. You may check which keys are on your keyring with the following command: 


    % pgp -kv
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses. 
(c) 1990-1994 Philip Zimmermann, Phil's Pretty Good Software. 11 Oct 94 
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc. 
Distributed by the Massachusetts Institute of Technology. 
Export of this software may be restricted by the U.S. government. 
Current time: 1997/04/02 23:23 GMT 
 
Key ring: '/pmdf/table/.pgp/pubring.pgp' 
Type bits/keyID    Date       User ID 
pub  1024/BFFA43E9 1997/04/02 PMDF MTA key <bsmtp@bsin.host0> 
pub  1024/6405957D 1997/03/17 PMDF MTA key <bsmtp@bsin.host0> 
2 matching keys found.

Once you have exchanged the keys, you should then be able to send digitally signed BSMTP parcels.

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