Lecture 9. E-mail Security and PGP


9.1 전자우편 보안의 필요성과 목표
9.2 메시지 암호화 알고리즘과 디지털 서명
9.3 PGP (Pretty Good Privacy) 개요
9.4 UNIX용 PGP 6.5.1 사용법
9.5 기타 전자 우편 보안 관련 사항들
 
 

9.1 전자우편 보안의 필요성과 목표


전자우편 보안 목표


일반 우편물과의 비교


전자우편의 보안 취약성 

        cs:/usr/mail> whoami                            
        root                                             
                                                         
        cs:/usr/mail> ls -l                             
        
        -rw-rw----   1 ahs      mail           0 11월  5일  10:13 ahs    
        .................
        -rw-rw----   1 rhee     mail       44455 11월 14일  14:28 rhee   
        -rw-rw----   1 root     mail       32136 11월  9일  17:29 root   
        -rw-rw----   1 route    mail       14340 11월 13일  11:08 route  
        .................                                       
                                                        
        cs:/usr/mail> cat rhee
        Message-Id: <199610....19.UAA16995@audio20.prognet.com>
        To: rhee@cs.sookmyung.ac.kr
        From: RealAudio Talking E-mail 
        Subject: Hear Near-CD Quality Audio Over Standard Modems
        
        Dear RealAudio Customer,
        Since you downloaded our free RealAudio Player a while back,
        you have heard some pretty amazing things on the Web.
        
        Now you can hear even more with RealAudio Player Plus,
        
         http://www.realaudio.com/bplus/index.html
        
        .................
        
        Rob Glaser                      Bruce Jacobsen
        Progressive Networks            Progressive Networks
        Chairman & CEO,                 President & COO,

9.2 메시지 암호화 알고리즘과 디지털 서명


암호화 알고리즘


디지털 서명


키 관리와 키 인증 모델


전자 우편 보안 도구

9.3 PGP (Pretty Good Privacy) 개요

9.4 UNIX용 PGP 6.5.1 사용법

al-linux:/home/rhee 1 > pgp -k  (키 관련 명령 보기)
                        
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

Key management functions:
To generate your own unique public/secret key pair:
   pgp -kg
To add a key file's contents to your public, secret key ring or key server:
   pgp -ka keyfile [keyring] 
To remove a key or user ID from your public, secret key ring or key server:
   pgp -kr userid [keyring | URL]
To edit your user ID or pass phrase:
   pgp -ke your_userid [keyring]
To extract (copy) a key from your public or secret key ring:
   pgp -kx userid keyfile [keyring | URL]
To view the contents of your public key ring or query the keyserver:
   pgp -kv[v] [userid] [keyring | URL]
To check signatures on your public key ring:
   pgp -kc [userid] [keyring]
To sign someone else's public key on your public key ring:
   pgp -ks her_userid [-u your_userid] [keyring]
To remove selected signatures from a userid on a keyring or key server:
   pgp -krs userid [keyring] 

al-linux:/home/rhee 2 > pgp -kg (키의 생성)
                        
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

Choose the public-key algorithm to use with your new key
1) DSS/DH (a.k.a. DSA/ElGamal) (default)
2) RSA
Choose 1 or 2: 1
               
Choose the type of key you want to generate
1) Generate a new signing key (default)
2) Generate an encryption key for an existing signing key
Choose 1 or 2: 1
               
Pick your DSS ``master key'' size:
1)  1024 bits- Maximum size (Recommended)
Choose 1 or enter desired number of bits: 1
                                          
Generating a 1024-bit DSS key.

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 <jqsmith@nai.com>
Enter a user ID for your public key: Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>

Enter the validity period of your signing key in days from 0 - 10950
0 is forever (the default is 0): 30

You need a pass phrase to protect your DSS 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:                              
Enter same pass phrase again:                              

PGP will generate a signing key. Do you also require an 
encryption key? (Y/n) 
Pick your DH key size:
1)  1024 bits- High commercial grade, secure for many years
2)  2048 bits- "Military" grade, secure for forseeable future
3)  3072 bits- Archival grade, slow, highest security
Choose 1, 2, 3, or enter desired number of bits: 1

Enter the validity period of your encryption key in days from 0 - 30
0 is forever (the default is 30):  

Note that key generation is a lengthy process.

PGP needs to generate some random data. This is done by measuring
the time intervals between your keystrokes. Please enter some
random text on your keyboard until the indicator reaches 100%.
Press ^D to cancel
                             
Enough, thank you.
....******* ..........******* . 
Make this the default signing key? (Y/n)  
                                         
..................******* ....******* 
Key generation completed.

al-linux:/home/rhee 3 > ls -al .pgp
total 12
drwx------   2 rhee     staff        1024 Aug 17 17:08 ./
drwx------   5 rhee     staff        1024 Aug 17 17:06 ../
-rw-------   1 rhee     staff        2117 Aug 17 17:06 PGPMacBinaryMappings.txt
-rw-------   1 rhee     staff         146 Aug 17 16:22 PGPgroup.pgr
-rw-------   1 rhee     staff         171 Aug 17 17:08 PGPsdkPreferences
-rw-------   1 rhee     staff           0 Aug 17 16:22 pgp.cfg
-rw-------   1 rhee     staff           0 Aug 17 16:22 pubring-bak-1.pkr
-rw-------   1 rhee     staff         921 Aug 17 17:08 pubring-bak-2.pkr
-rw-------   1 rhee     staff         921 Aug 17 17:08 pubring.pkr
-rw-------   1 rhee     staff         512 Aug 17 17:08 randseed.rnd
-rw-------   1 rhee     staff           0 Aug 17 16:22 secring-bak-1.skr
-rw-------   1 rhee     staff        1007 Aug 17 17:08 secring-bak-2.skr
-rw-------   1 rhee     staff        1007 Aug 17 17:08 secring.skr

al-linux:/home/rhee 4 > pgp -kx rhee rhee.asc (키의 추출)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

Extracting from keyring '/home/rhee/.pgp/pubring.pkr', userid "rhee".

Key extracted to file 'rhee.asc'.

al-linux:/home/rhee 5 > cat rhee.asc
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: PGP 6.5.1
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=wFqS
-----END PGP PUBLIC KEY BLOCK-----

al-linux:/home/rhee 6 > Mail
Mail version 8.1 6/6/93.  Type ? for help.
"/var/spool/mail/rhee": 2 messages 1 new
    1 MAILER-DAEMON@al-lin  Sat Jul 31 18:29  12/523   "DON'T DELETE THIS MES"
>N  2 dummy1@al-linux.sook  Sat Aug 21 16:23  36/1712  "PGP Key from Dummy 1"
& 2
Message 2:
From dummy1  Sat Aug 21 16:23:47 1999
Date: Sat, 21 Aug 1999 16:23:47 +0900
From: Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
To: rhee@al-linux.sookmyung.ac.kr
Subject: PGP Key from Dummy 1

-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: PGP 6.5.1

mQGiBDeliWgRBADq0P5VyiqjMx5CGBCdtDeBZDjV2BbUVJZCrvBmARdIuwr6A1/r
rjZ+I8vZ7w5Gf1S9clT4JvAY/EMwpt9mqojswLsg2IhyCzp4+AljChb+x5jwXHYX
LrLJjK3FsJ/7S+pJzx1saJd192qwJNtCzhLoiQuzmdGt7K8gtSUIKGRKvQCg/7qJ
zhwemqFIKr2GHrSSsMIUyAkEAJAuGYJ33lSyOI7Euq+avSmoV+3AiiAaALE3kXgW
MumcG7+J3EJNtIZNNbPfH0rouJZMHLJwfORLoJgm0Td+rYX+SoOo5JSmG9+vIKmu
IHPJOqb+VOEhVBAya5B5b5Zp2xd2bIqXkEIxsqC2apOYWB+FE+lFT1bzisnmxsSk
Jw6qA/98FP0GyCmh2rz9nOwu6p9Hp0BWsjmeHUKRcv2EtB+9EqRWvbr/yMk5Ac5E
/edJO897UZ14dT1/oURLznsNfSXh2YFl7ODUAvazG1o99HEkxPjQs9Rml870I6Ku
13vRr5nPBUUOK9w4ccgXyXU2PdB7hYVDrV3r0AQND4LffyVNArQpRHVtbXkgMSA8
ZHVtbXkxQGFsLWxpbnV4LnNvb2tteXVuZy5hYy5rcj6JAE4EEBECAA4FAjeliWgE
CwMBAgIZAQAKCRChjLBZl3O7eHWaAKC0B4U3AxYfVWpsB/w+OyRPoEx4xACgnNAu
a78gf95aBrJB1e8mnEnUXTa5AQ0EN6WJbxAEAPJRkXFc+SEpW+Ai/4ATO3j4z0Em
o0n3aeim9T2srwt/UtCIe0l7EsGREOpSqPuxKAX/NWjiIkEkwAm5NX9aiaq8MYWf
hlJ22IZLsnRAgeXK39s6Z4Xf8oTHgJnh2YEv761j2dIlVjZycsZ7DaroGnlQnsB+
94SdlSyO/J2ozDN9AAICA/9gPqmMGXK3zsWUMLwCB8mdA73V1xSODPFjXV4fVIBB
NcbqjjsXhHxDHGh1u1UCee3jxsWpXDeioJRCCLdqTk+PlTtnNoGoaKRpLLmPtq70
uQly7NjMf7IupCNVX5DuS/PaNha4ooe4wVZNAM664Mddno4UY8jPVxteHEcb6Or2
zYkARgQYEQIABgUCN6WJbwAKCRChjLBZl3O7eJ/iAKCr3D35ceiuCQJmLQFZFixO
G7nbXQCePKf21xyuMdKHTjx+ouCW5HaE7gI=
=QlaB
-----END PGP PUBLIC KEY BLOCK-----

& w 2 dummy.asc
"dummy.asc" [New file]
& x

al-linux:/home/rhee 7 > cat dummy.asc
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: PGP 6.5.1
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=QlaB
-----END PGP PUBLIC KEY BLOCK-----

al-linux:/home/rhee 8 > pgp -kv (키 보기)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.


Type bits      keyID      Date       User ID
DSS  1024/1024 0x0A9C4A91 1999/08/17 expires 1999/09/16                                      
                                      *** DEFAULT SIGNING KEY ***
                                     Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
1 matching key found.

al-linux:/home/rhee 9 > pgp -kvv (키 자세히 보기)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.


Type bits      keyID      Date       User ID
DSS  1024      0x0A9C4A91 1999/08/17 expires 1999/09/16
 DH  1024      0x0A9C4A91 1999/08/17 expires 1999/09/16
                                      *** DEFAULT SIGNING KEY ***
                                     Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
sig            0x0A9C4A91             Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
1 matching key found.

al-linux:/home/rhee 10 > pgp -ka dummy.asc (키의 추가)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.


Looking for new keys...
DSS  1024/1024 0x9773BB78 1999/08/02 Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
sig?           0x9773BB78             (Unknown signator, can't be checked)

keyfile contains 1 new keys. Add these keys to keyring ''? (Y/n)   

Keyfile contains:
   1 new key(s)

al-linux:/home/rhee 11 > pgp -kvv
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.


Type bits      keyID      Date       User ID
DSS  1024      0x9773BB78 1999/08/02 
 DH  1024      0x9773BB78 1999/08/02 Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
sig            0x9773BB78             Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
DSS  1024      0x0A9C4A91 1999/08/17 expires 1999/09/16
 DH  1024      0x0A9C4A91 1999/08/17 expires 1999/09/16
                                      *** DEFAULT SIGNING KEY ***
                                     Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
sig            0x0A9C4A91             Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
2 matching keys found.

al-linux:/home/rhee 12 > cat sample
alias gcc       'gcc -ansi -O0'
alias h         history
alias help      man
alias df        'df -k'
alias lo        logout

al-linux:/home/rhee 13 > pgp -c sample (개인 파일의 암호화)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

You need a pass phrase to encrypt the file. 
Enter pass phrase:                        
Enter same pass phrase again:                        

Ciphertext file: sample.pgp

al-linux:/home/rhee 14 > pgp -ca sample (개인 파일의 암호화, ASCII 출력)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.


You need a pass phrase to encrypt the file. 
Enter pass phrase: 
Enter same pass phrase again: 

Transport armor file: sample.asc

al-linux:/home/rhee 15 > ls -l sample*
-rw-r--r--   1 rhee     staff         103 Aug 21 16:32 sample
-rw-------   1 rhee     staff         219 Aug 21 16:34 sample.asc
-rw-------   1 rhee     staff         101 Aug 21 16:33 sample.pgp

al-linux:/home/rhee 16 > cat sample.asc
-----BEGIN PGP MESSAGE-----
Version: PGP 6.5.1

pGNMhPgqZCT1WDlcoSbS5tgiJxZY3Mj0r+xkBskKif54SeqlGp3N29f8tT+UdNoh
oyX5OTHUK+xs0vyrzSOCc2HWoJpuE1xOESvtBXfC4VQO0qOzdRHLYMuodn4YEWYM
ti6oQ5M=
=+mDT
-----END PGP MESSAGE-----

al-linux:/home/rhee 17 > rm sample

al-linux:/home/rhee 18 > pgp sample.pgp (암호화된 파일 보기: 해독 및 서명 확인)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

File is encrypted.  You need a pass phrase to decrypt this file.

Enter pass phrase:                         

Plaintext filename: sample

al-linux:/home/rhee 19 > cat sample
alias gcc       'gcc -ansi -O0'
alias h         history
alias help      man
alias df        'df -k'
alias lo        logout

al-linux:/home/rhee 20 > pgp -e sample rhee dummy1 (rhee와 dummy1에게 보낼 파일을 암호화)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

Recipients' public key(s) will be used to encrypt.

Key for user ID: Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
1024-bit DSS key, Key ID 0x0A9C4A91, created 1999/08/17, expires 1999/09/16
Key can sign. 

Key for user ID: Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
1024-bit DSS key, Key ID 0x9773BB78, created 1999/08/02
WARNING:  Because this public key is not certified with a trusted
signature, it is not known with high confidence that this public key
actually belongs to: "Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>".

Are you sure you want to use this public key (y/N)? y

Output file 'sample.pgp' already exists.  Overwrite (y/N)? y

Ciphertext file: sample.pgp

al-linux:/home/rhee 21 > ls -l sample*
-rw-------   1 rhee     staff         103 Aug 21 16:35 sample
-rw-------   1 rhee     staff         219 Aug 21 16:34 sample.asc
-rw-------   1 rhee     staff         653 Aug 21 16:39 sample.pgp

al-linux:/home/rhee 22 > pgp sample.pgp
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

File is encrypted.  Secret key is required to read it.

Key for user ID: Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
1024-bit DSS key, Key ID 0x0A9C4A91, created 1999/08/17, expires 1999/09/16
Key can sign. 
You need a pass phrase to unlock your secret key.

Enter pass phrase:                      

Output file 'sample' already exists.  Overwrite (y/N)? N

Enter new file name: sample1

Plaintext filename: sample1

al-linux:/home/rhee 23 > cat sample1
alias gcc       'gcc -ansi -O0'
alias h         history
alias help      man
alias df        'df -k'
alias lo        logout

al-linux:/home/rhee 24 > pgp -s sample (메시지 서명)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

A secret key is required to make a signature. 
You need a pass phrase to unlock your secret key.
Key for user ID "Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>"

Enter pass phrase:                   

Passphrase is good

Output file 'sample.pgp' already exists.  Overwrite (y/N)? y

Signature file: sample.pgp

al-linux:/home/rhee 25 > ls -l sample*
-rw-------   1 rhee     staff         103 Aug 21 16:35 sample
-rw-------   1 rhee     staff         219 Aug 21 16:34 sample.asc
-rw-------   1 rhee     staff         157 Aug 21 16:41 sample.pgp
-rw-------   1 rhee     staff         103 Aug 21 16:40 sample1

al-linux:/home/rhee 26 > pgp -esa sample dummy1 (sample이라는 
    파일을 dummy1이 읽을 수 있도록 암호화하면서, rhee가 서명)
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.


A secret key is required to make a signature. 

Recipients' public key(s) will be used to encrypt.

You need a pass phrase to unlock your secret key.
Key for user ID "Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>"

Enter pass phrase:                    

Passphrase is good

Key for user ID: Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
1024-bit DSS key, Key ID 0x9773BB78, created 1999/08/02
WARNING:  Because this public key is not certified with a trusted
signature, it is not known with high confidence that this public key
actually belongs to: "Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>".

Are you sure you want to use this public key (y/N)?y

Output file 'sample.asc' already exists.  Overwrite (y/N)? y

Transport armor file: sample.asc

al-linux:/home/rhee 27 > ls -l sample*
-rw-------   1 rhee     staff         103 Aug 21 16:35 sample
-rw-------   1 rhee     staff         702 Aug 21 16:42 sample.asc
-rw-------   1 rhee     staff         157 Aug 21 16:41 sample.pgp
-rw-------   1 rhee     staff         103 Aug 21 16:40 sample1

al-linux:/home/rhee 28 > cat sample.asc
-----BEGIN PGP MESSAGE-----
Version: PGP 6.5.1
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=c9bj
-----END PGP MESSAGE-----

al-linux:/home/rhee 29 > Mail -s "Signed and Encrypted" dummy1 < sample.asc
al-linux:/home/rhee 27 > telnet al-linux
Trying 203.252.195.104...
Connected to al-linux.sookmyung.ac.kr.
Escape character is '^]'.

ALzzA Linux release 5.2 (PatchMan Dreams of World Domination)
Kernel 2.0.36 on an i686
login: dummy1
Password:          
Last login: Sat Aug 21 16:20:42 from al-linux
You have new mail.
al-linux:/home/user/dummy1 1 > Mail
Mail version 8.1 6/6/93.  Type ? for help.
"/var/spool/mail/dummy1": 2 messages 2 new
>N  1 rhee@al-linux.sookmy  Sat Aug 21 16:33  35/1704  "Rhee's Public Key"
 N  2 rhee@al-linux.sookmy  Sat Aug 21 16:44  27/1129  "Signed and Encrypted"
& w 1 rhee.asc
"rhee.asc" [New file]& w 2 m.asc
& w 2 m.asc
"m.asc" [New file]
& x

al-linux:/home/user/dummy1 2 > pgp -kvv
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

Type bits      keyID      Date       User ID
DSS  1024      0x9773BB78 1999/08/02 
 DH  1024      0x9773BB78 1999/08/02 *** DEFAULT SIGNING KEY ***
                                     Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
sig            0x9773BB78             Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
1 matching key found.

al-linux:/home/user/dummy1 3 > pgp -ka rhee.asc
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

Looking for new keys...
DSS  1024/1024 0x0A9C4A91 1999/08/17 Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>
sig?           0x0A9C4A91             (Unknown signator, can't be checked)

keyfile contains 1 new keys. Add these keys to keyring ''? (Y/n) 

Keyfile contains:
   1 new key(s)

al-linux:/home/user/dummy1 4 > pgp m.asc
Pretty Good Privacy(tm) Version 6.5.1
(c) 1999 Network Associates Inc.
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Export of this software may be restricted by the U.S. government.

File is encrypted.  Secret key is required to read it.

Key for user ID: Dummy 1 <dummy1@al-linux.sookmyung.ac.kr>
1024-bit DSS key, Key ID 0x9773BB78, created 1999/08/02
Key can sign. 
You need a pass phrase to unlock your secret key.

Enter pass phrase:                    
Good signature from user "Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>".
Signature made 1999/08/21 07:43 GMT

WARNING:  Because this public key is not certified with a trusted
signature, it is not known with high confidence that this public key
actually belongs to: "Gwangsoo Rhee <rhee@al-linux.sookmyung.ac.kr>".

Plaintext filename: m

9.5 기타 전자 우편 보안 관련 사항들


MIME 보안


발신자 부인 방지(Sender Non-repudiation)


메시지 수신 사실 및 내용 확인 통보


발신 사실이나 내용 증명


Traffic-flow 기밀성


발신자 익명성


Spam (junk e-mail)


전자 우편 바이러스