Transcript No Slide Title
ECE-8843 http://www.ece.gatech.edu/~copeland/jac/8843-03/ Prof. John A. Copeland [email protected]
404 894-5177 fax 404 894-0035 Office: GCATT Bldg 579 email or call for office visit, or call Kathy Cheek, 404 894-5696 Chapter 5a - Pretty Good Privacy (PGP) Email
Electronic Mail In 1982, ARPANET email proposals were published as RFC 821 (www.ietf.org
/rfc/rfc0821.txt) and RFC 822
•
Email services since are based on these RFC's
•
CCITT X.400 & ISO MOTIS grew and waned as competitors
•
"User Agents" UA, and "Message Transfer Agents" MTA Three parts to an email message:
•
Envelope - information used to forward the contents
•
Header - standard strings, some added in route.
>
To: Cc: Bcc: From: Sender:
>
Received: (added in route), Return-Path: (by final MTA)
>
MIME headers added by RFC 1341 and 1521
>
A. S. Tanenbaum, "Computer Networks," (3rd ed.) p.651
2
MIME Headers
Multipurpose Internet Mail Extensions (MIME) RFC 1341 and RFC 1521
•
MIME -Version:
•
Content-Description:
• > >
Content-ID: version number human-readable string unique identifier
•
Content-Transfer-Encoding: body encoding
> >
ASCII (Plain, quoted-printable, or Richtext) Binary (base64)
•
Content-Type: nature of the message Image (gif, jpeg), Video (mpeg), Application (Postscript, octet-stream)
>
A.S.Tanenbaum, "Computer Networks," (3rd ed.) p.653
3
Received: from didier.ee.gatech.edu (didier.ee.gatech.edu
[130.207.230.10]) by eagle.gcatt.gatech.edu (8.8.8+Sun/8.7.1) with ESMTP id UAA00818 for
>; Fri, 30 Jul 1999 20:00:33 -0400 (EDT) Received: from NOP (152.159.60.175) by bwnewsletter.com with SMTP (Eudora Internet Mail Server 2.1); Fri, 30 Jul 1999 16:24:21 -0400 Message-Id: <[email protected]> X-Sender: [email protected] (Unverified) X-Mailer: Windows Eudora Light Version 1.5.4 (32) Mime-Version: 1.0
Date: Fri, 30 Jul 1999 16:21:37 -0400 To: [email protected] (note: I was on a Bcc: list) From: BW Online
4
$ nslookup -q=MX ee.gatech.edu (nslookup -> host) ee.gatech.edu preference = 10, mail exchanger = mail.ee.gatech.edu
ee.gatech.edu nameserver = eeserv.ee.gatech.edu
ee.gatech.edu nameserver = duchess.ee.gatech.edu
ee.gatech.edu nameserver = didier.ee.gatech.edu
mail.ee.gatech.edu internet address = 130.207.230.10
eeserv.ee.gatech.edu internet address = 130.207.230.5
duchess.ee.gatech.edu internet address = 130.207.230.13
didier.ee.gatech.edu internet address = 130.207.230.10
5
$ nslookup -q=mx mcgraw-hill.com
Non-authoritative answer: mcgraw-hill.com preference = 20, mail exchanger = interlock.mgh.com
Authoritative answers can be found from: mcgraw-hill.com nameserver = NS-01A.ANS.NET
mcgraw-hill.com nameserver = NS-01B.ANS.NET
mcgraw-hill.com nameserver = NS-02A.ANS.NET
mcgraw-hill.com nameserver = NS-02B.ANS.NET
NS-01A.ANS.NET internet address = 199.221.47.7
NS-01B.ANS.NET internet address = 199.221.47.8
NS-02A.ANS.NET internet address = 207.24.245.179
NS-02B.ANS.NET internet address = 207.24.245.178
6
$ nslookup 198.45.19.20
Name: gw2.mcgraw-hill.com
Address: 198.45.19.20
$ nslookup 152.159.60.175
*** can't find 152.159.60.175: Non-existent host/domain
$ traceroute 152.159.60.175
1 24.88.12.129 (24.88.12.129 ): 17ms 2 stn-mtn-rtrb.atl.mediaone.net. (24.88.0.254 ): 18ms 3 24.93.64.69 (24.93.64.69 ): 20ms 4 24.93.64.61 (24.93.64.61 ): 17ms 5 24.93.64.57 (24.93.64.57 ): 25ms 6 sgarden-sa-gsr.carolina.rr.com. (24.93.64.30 ): 26ms 7 roc-gsr-greensboro-gsr.carolina. (24.93.64.17 ): 29ms 8 24.93.64.45 (24.93.64.45 ): 38ms 9 sjbrt01-vnbrt01.rr.com. (24.128.6.6 ): 41ms 10 pnbrt01-vnbrt01.rr.com. (24.128.6.85 ): 42ms 11 p217.t3.ans.net. (192.157.69.52 ): 51ms 12 h13-1.t32-0.new-york.t3.ans.net. (140.223.33.21 ): 49ms 13 f0-0.cnss33.new-york.t3.ans.net. (140.222.32.193 ): 53ms 14 s0.enss3339.t3.ans.net. (199.222.77.70 ): 61ms 15 * * * 16 * * * 7
Security Services for Email
Privacy - only for intended recipient Authentication - confidence in ID of sender Integrity - assurance of no data alteration Non-repudiation - proof that sender sent it Proof of submission - was sent to email server Proof of delivery - was received by addressee Message flow confidentiality - no one can know a message was sent (anti-traffic analysis)
8
Security Services for Email - 2
Anonymity - sender's ID hidden Containment - message forwards to limited area Audit - events recorded Accounting - user statistics for allocating costs Self-destruct - can not forward or store Message sequence integrity - all messages arrived in correct order 9
Establishing Keys • Public Key Certification • Exchange Public Keys
Privacy
Multiple Recipients • Encrypt message m with session key, S • Encrypt S with each recipient's key • Send: {S; Kbob}, {S; Kann}, ... , {m; S} Authentication of Source • Hash (MD4, MD5, SHA1) of message, encrypt with private key (provides ciphertext/plaintext pair) • Secret Key K: MIC is hash of K+m, or CBC residue with K (assuming message not encrypted with K).
10
Message Integrity
The source authentication methods that include a hash of the message provide MIC
Non-repudiation
Public-key signing provides non-repudiation.
Secret-key method requires a "Notary" to "Sign" a time-stamp + hash of the message
Proof of Delivery
Acknowledge before reading - can't prove m was read.
Acknowledge after - may have read without signing.
11
Proof of Submission
•
CC yourself (unfortunately headers easily modified) - CC Notary (if recipient not in Bcc) Flow Confidentiality
•
Encrypt message and headers, to third party.
•
Send from the corner Cyber Cafe, fake HotMail account Anonymity
•
Several Web site services available Containment
•
Network Admin can set up filter tables on routers.
12
Names and Addresses
X.500 Name (ISO standard) • ?/C=US/O=CIA/OU=drugs/PN='Manny Norriega' Internet Name • [email protected] or [email protected]
•
Old message - later Non-reputiation
• Need Notary to sign hash of message, Certificate used to authenticate Public Key, and current CRL 13
Compress Image Compress Text
From "PGP Freeware for MacOS, User's Guide" Version 6.5, Network Associates, Inc., www.pgp.com
14
with signature attached if there is one
From "PGP Freeware for MacOS, User's Guide" Version 6.5, Network Associates, Inc., www.pgp.com
15
compressed, 16
17
18
To: "Khawar Azad"
Cc: Bcc: X-Attachments: Radix-64 encoding of a binary (all possible 8-bit bytes) message 6-bits at a time into 64 printable ASCII characters (A-Z, a-z , 0-9, +, / bytes 65-90, 97 122, 48-57, 47, 43) pad with =.
-----BEGIN PGP MESSAGE---- Version: PGPfreeware 6.5.2 for non-commercial use
20
PGP Certificates
Anyone can issue a Certificate to anyone else Certificates can be revoked by the issuer
Privacy Enhanced Mail, another standard
Where PEM expands data into canonical form, • (+33% for text, +78% after encryption) PGP compresses data using ZIP(-50%), encrypts, then (optionally) converts to base64 (+33%) 21
Things of which to be aware
Neither PEM or PGP encode mail headers • Subject can give away useful info • To and From give an intruder traffic analysis info PGP gives recipient the original file name and modification date PEM may be used in a local system with unknown trustworthyness of certificates Certificates often verify that sender is "John Smith" but he may not be the "John Smith" you think (PGP allows pictures in certificates) 22