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Pretty Good Privacy (PGP) Email Encryption

Learn about Pretty Good Privacy (PGP), an email encryption method that provides secure communication over the internet. Understand the different parts of an email message, such as the envelope and header. Discover how MIME headers are used to add additional information to emails. Explore the process of sending and receiving emails through different servers. Get insights into the importance of email security and how PGP helps protect sensitive information.

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Pretty Good Privacy (PGP) Email Encryption

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  1. ECE-6612 http://www.ece.gatech.edu/~copeland/jac/6612/ Prof. John A. Copeland john.copeland@ece.gatech.edu 404 894-5177 fax 404 894-0035 Office: Centergy 5138 (VL W315 MWF a.m.) email or call for office visit, or call Kathy Cheek, 404 894-5696 Chapter 5a - Pretty Good Privacy (PGP) Email

  2. 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 (+ many later) • 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

  3. MIME Headers Multipurpose Internet Mail Extensions (MIME) RFC 1341 and RFC 1521 • MIME -Version: version number • Content-Description: human-readable string • Content-ID: 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

  4. 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 <copeland@eagle.gcatt.gatech.edu>; Fri, 30 Jul 1999 20:00:35 -0400 (EDT) Received: from bwnewsletter.com (gw2.mcgraw-hill.com [198.45.19.20]) by didier.ee.gatech.edu (8.9.0/8.9.0) with ESMTP id UAA16500 for <jcopeland@ ece.gatech.edu >; 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: <1.5.4.32.19990730202137.00672900@businessweek.com> X-Sender: mustread@businessweek.com (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: bwnewsletter@bwnewsletter.com (note: I was on a Bcc: list) From: BW Online <insider@businessweek.com> Subject: BUSINESS WEEK ONLINE INSIDER -- July 30 Content-Type: text/plain; charset="us-ascii" Content-Length: 7694 4

  5. $ 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

  6. $ 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

  7. $ nslookup 198.45.19.20 [can also use “host” or “dig”] 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 [on MS Windows, open DOS, type “tracert”] 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

  8. $ whois 152.159.60.175 OrgName: McGraw Hill, Inc OrgID: MCGRAW Address: 148 Princeton Htstown Rd City: Hightstown StateProv: NJ PostalCode: 08520 Country: US NetRange: 152.159.0.0 - 152.159.255.255 CIDR: 152.159.0.0/16 NetName: MHP-NET NameServer: AUTH111.NS.UU.NET NameServer: AUTH120.NS.UU.NET Comment: RegDate: 1992-03-18 Updated: 2004-04-01 RTechHandle: MW1053-ARIN RTechName: Weyman, Mike RTechPhone: +1-555609-426-5291 RTechEmail: mike_weyman@mgh.com RTechHandle: JGE8-ARIN RTechName: Gervasio, John RTechPhone: +1-555-426-5017 RTechEmail: john_gervasio@mgh.com OrgTechHandle: HOSTM339-ARIN OrgTechName: hostmaster OrgTechPhone: +1-555-426-5291 OrgTechEmail: hostmaster@mgh.com # ARIN WHOIS database, last updated 2006-09-24 19:10 # Enter ? for additional hints on searching ARIN's WHOIS database. 8

  9. 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) 9

  10. 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 10

  11. Privacy Establishing Keys • Public Key Certification • Exchange Public Keys 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). 11

  12. 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. 12

  13. 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. 13

  14. Names and Addresses X.500 Name (ISO standard) • ?/C=US/O=CIA/OU=drugs/PN='Manny Norriega' Internet Name • m_noriega@mail.drugpc.cia.gov or manny@cia.gov • <user account name> @ <DNS host name or alias> • using the alias "mail" lets mail server program be moved from one host to another • in ece.gatech.edu domain, "mail" is an alias for "didier", also any email to "ece.gatech.edu"is ok. Old message - later Non-reputiation • Need Notary to sign hash of message, Certificate used to authenticate Public Key, and current CRL 14

  15. Compress Text Compress Image PGP Email: Sign (optional) before Encryption (also optional) 15 From "PGP Freeware for MacOS, User's Guide" Version 6.5, Network Associates, Inc., www.pgp.com

  16. with signature attached if there is one From "PGP Freeware for MacOS, User's Guide" Version 6.5, Network Associates, Inc., www.pgp.com 16

  17. PGP Email Receiver Private Key Ring Public Key Ring compressed, PGP Email Sender p.144-145 ed.3 17

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  19. Every 3 bytes split into 4 6-bit numbers n = 0 to 63 printable characters a-z A-Z 0-9 + - in a received message, “=“, “>”, CR, LF, ... are ignored 19

  20. To: ”Jim Jones" <jim_jones@hotmail.com> From: John Copeland <john.copeland@ece.gatech.edu> Subject: ECE8813 : PGP Endeavor... Cc: Bcc: X-Attachments: -----BEGIN PGP MESSAGE----- Version: PGPfreeware 6.5.2 for non-commercial <http://www.pgp.com> qANQR1DBwU4D6cjDU+QAxCwQB/9IZFOIuDSIIQbwa28SQ63DDioFb4bH4bmKfopX cvdDVQ1X53fSJzyLt12RslfQToje8YxRNidYMNg1zDTT7CR9q7LRFoAwBFVtQhWJ jFNXn1+aE8oePReMi6vS0DXSSDfgDuUb1R+c8htHoeik6Oebe9R90J3d51yyCojV AHT01kWlpvJIZGKyT3PdCh9wlr1hQsUGto10t32fBGsJCXew/EClb554AnyYSzP8 KAjuw1NdKOBlze0DCiO6Z5z+DAxAwlqTxcm42tthF5zFbTk4UKV6ORzIuHmRO7xR 5Io5nlM7T11PDaWqsjLr2ttrSySzARt5fAJ9l1mOH+hSl1YebRjZPaxWw+bsYuqN a0GYr2UdwgE1u5HQuhZ+bOIbSliShfKiNuDGHe6VJrchROHnC9Po2JWAOD7wMFq6 STZ/MPGzViaCUaaWPLSKleiURUh4Ly5/LaNYkaumO9vh+241FPqtZKqRVmHRg6dY UdgoI3yfc3JrvepFQT1yeRjEVrLQiUtyhcwdVoLjofgerGAfe3YuDCxM6wLIuCf7 Ro9edu01qTiXJj25cXHxeNMdA1txLxR3ontbExow+ML5kxs= =68Hd -----END PGP MESSAGE----- Radix-64 encoding of a binary (all 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 =. 20

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  22. 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%) 22

  23. Things of which to be aware Neither PEM nor PGP encodes 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) 23

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