1. CSCE 815 Network Security Lecture 12 Email Security S/MIME February 25, 2003

2. – 2 – CSCE 815 Sp 03 PGP Operation – Summary

3. – 3 – CSCE 815 Sp 03 ZIV compression Compression based on recognizing repetitions Based on Jacab Ziv and Abraham Lempel (Ziv-Lempel or LZ77) 0r 00 00011010 1101 0r 00 00011010 1101 Sliding history buffer --- look-ahead buffer Decompression easy.

4. – 4 – CSCE 815 Sp 03 Radix 64 Conversion Table 5.9 – 6 bit Input versus character output

5. – 5 – CSCE 815 Sp 03 RFC 822 Defines a format for text messages that are sent via email MIME is an extension for RFC 822 intended to address some problems  SMTP cannot handle binaries  SMTP cannot handle extended character sets of specific languages  SMTP may reject large messages  SMTP fails to handle ASCII  EBCIDIC translations  SMTP gateways cannot handle non textual data

6. – 6 – CSCE 815 Sp 03 Multipurpose Internet Mail Extensions MIME - Adds new headers (RFC 822,2045) MIME 5 header fields MIME-version Content-Type Content-Transfer-Encoding Content-ID Content-Description

7. – 7 – CSCE 815 Sp 03 Content Types  Text: plain, richtext, enriched  Multipart: mixed, parallel, parts can be analyzed in parallel digest, an electronic mail digest alternative  Message: RFC822, partial, external-body  Application: octet-stream, postscript  Image: jpeg, gif  Audio  Video: mpeg

8. – 8 – CSCE 815 Sp 03 Content-Transfer-Encodings Defined RFC 1521  7bit – NVT ASCII, the default  Binary – not only non-ASCII characters, but lines may be long  Quoted-printable – mostly ASCII text  Base-64 (radix 64)  8bit non-ASCII have the eighth bit set  X-token – a nonstandard encoding

9. – 9 – CSCE 815 Sp 03 S/MIME Secure/Multipurpose Internet Mail Extension S/MIME will probably emerge as the industry standard. PGP for personal e-mail security

10. – 10 – CSCE 815 Sp 03 Simple Mail Transfer Protocol (SMTP, RFC 822) SMTP Limitations - Can not transmit, or has a problem with: executable files, or other binary files (jpeg image) “national language” characters (non-ASCII) messages over a certain size ASCII to EBCDIC translation problems lines longer than a certain length (72 to 254 characters)

11. – 11 – CSCE 815 Sp 03 Header fields in MIME MIME-Version: Must be “1.0” -> RFC 2045, RFC 2046 Content-Type: More types being added by developers (application/word) Content-Type: More types being added by developers (application/word) Content-Transfer-Encoding: How message has been encoded (radix-64) Content-ID: Unique identifying character string. Content Description: Needed when content is not readable text (e.g.,mpeg)

12. – 12 – CSCE 815 Sp 03 User Agent Role S/MIME uses Public-Key Certificates - X.509 version 3 signed by Certification Authority Functions: Key Generation - Diffie-Hellman, DSS, and RSA key-pairs. Registration - Public keys must be registered with X.509 CA. Certificate Storage - Local (as in browser application) for different services. Signed and Enveloped Data - Various orderings for encrypting and signing.

13. – 13 – CSCE 815 Sp 03 User Agent Role Example: Verisign (www.verisign.com) Class-1: Buyer’s email address confirmed by emailing vital info. Class-2: Postal address is confirmed as well, and data checked against directories. Class-3: Buyer must appear in person, or send notarized documents.

14. – 14 – CSCE 815 Sp 03 S/MIME Functions enveloped data encrypted content and associated keys signed data encoded message + signed digest clear-signed data cleartext message + encoded signed digest signed & enveloped data nesting of signed & encrypted entities

15. – 15 – CSCE 815 Sp 03 S/MIME Cryptographic Algorithms hash functions: SHA-1 & MD5 digital signatures: DSS & RSA session key encryption: ElGamal & RSA message encryption: Triple-DES, RC2/40 and others have a procedure to decide which algorithms to use

16. – 16 – CSCE 815 Sp 03 S/MIME Certificate Processing S/MIME uses X.509 v3 certificates managed using a hybrid of a strict X.509 CA hierarchy & PGP’s web of trust each client has a list of trusted CA’s certs and own public/private key pairs & certs certificates must be signed by trusted CA’s

17. – 17 – CSCE 815 Sp 03 Certificate Authorities have several well-known CA’s Verisign one of most widely used Verisign issues several types of Digital IDs with increasing levels of checks & hence trust ClassIdentity ChecksUsage 1name/email checkweb browsing/email 2+enroll/addr checkemail, subs, s/w validate 3+ID documentse-banking/service access

18. – 18 – CSCE 815 Sp 03 IP Security have considered some application specific security mechanisms eg. S/MIME, PGP, Kerberos, SSL/HTTPS however there are security concerns that cut across protocol layers would like security implemented by the network for all applications

19. – 19 – CSCE 815 Sp 03 IPSec general IP Security mechanisms provides authentication confidentiality key management applicable to use over LANs, across public & private WANs, & for the Internet

20. – 20 – CSCE 815 Sp 03 IPSec Uses

21. – 21 – CSCE 815 Sp 03 Benefits of IPSec in a firewall/router provides strong security to all traffic crossing the perimeter is resistant to bypass is below transport layer, hence transparent to applications can be transparent to end users can provide security for individual users if desired

22. – 22 – CSCE 815 Sp 03 IP Security Architecture specification is quite complex defined in numerous RFC’s incl. RFC 2401/2402/2406/2408 many others, grouped by category mandatory in IPv6, optional in IPv4

23. – 23 – CSCE 815 Sp 03 IPSec Services Access control Connectionless integrity Data origin authentication Rejection of replayed packets a form of partial sequence integrity Confidentiality (encryption) Limited traffic flow confidentiality

24. – 24 – CSCE 815 Sp 03 Security Associations a one-way relationship between sender & receiver that affords security for traffic flow defined by 3 parameters: Security Parameters Index (SPI) IP Destination Address Security Protocol Identifier has a number of other parameters seq no, AH & EH info, lifetime etc have a database of Security Associations

25. – 25 – CSCE 815 Sp 03 Authentication Header (AH) provides support for data integrity & authentication of IP packets end system/router can authenticate user/app prevents address spoofing attacks by tracking sequence numbers based on use of a MAC HMAC-MD5-96 or HMAC-SHA-1-96 parties must share a secret key

26. – 26 – CSCE 815 Sp 03 Authentication Header

27. – 27 – CSCE 815 Sp 03 Transport & Tunnel Modes

28. – 28 – CSCE 815 Sp 03 Encapsulating Security Payload (ESP) provides message content confidentiality & limited traffic flow confidentiality can optionally provide the same authentication services as AH supports range of ciphers, modes, padding incl. DES, Triple-DES, RC5, IDEA, CAST etc CBC most common pad to meet blocksize, for traffic flow

29. – 29 – CSCE 815 Sp 03 Encapsulating Security Payload

30. – 30 – CSCE 815 Sp 03 Transport vs Tunnel Mode ESP transport mode is used to encrypt & optionally authenticate IP data data protected but header left in clear can do traffic analysis but is efficient good for ESP host to host traffic tunnel mode encrypts entire IP packet add new header for next hop good for VPNs, gateway to gateway security

31. – 31 – CSCE 815 Sp 03 Combining Security Associations SA’s can implement either AH or ESP to implement both need to combine SA’s form a security bundle have 4 cases (see next)

32. – 32 – CSCE 815 Sp 03 Combining Security Associations

33. – 33 – CSCE 815 Sp 03 Key Management handles key generation & distribution typically need 2 pairs of keys 2 per direction for AH & ESP manual key management sysadmin manually configures every system automated key management automated system for on demand creation of keys for SA’s in large systems has Oakley & ISAKMP elements

34. – 34 – CSCE 815 Sp 03 Oakley a key exchange protocol based on Diffie-Hellman key exchange adds features to address weaknesses cookies, groups (global params), nonces, DH key exchange with authentication can use arithmetic in prime fields or elliptic curve fields

35. – 35 – CSCE 815 Sp 03 ISAKMP Internet Security Association and Key Management Protocol provides framework for key management defines procedures and packet formats to establish, negotiate, modify, & delete SAs independent of key exchange protocol, encryption alg, & authentication method

36. – 36 – CSCE 815 Sp 03 ISAKMP

37. – 37 – CSCE 815 Sp 03 Summary have considered: IPSec security framework AH ESP key management & Oakley/ISAKMP

38. – 38 – CSCE 815 Sp 03 Chapter 6 IP Security Internetworking and Internet Protocols (Appendix 6A) IP Security Overview IP Security Architecture Authentication Header Encapsulating Security Payload Combinations of Security Associations Key Management

39. – 39 – CSCE 815 Sp 03 TCP/IP Example

40. – 40 – CSCE 815 Sp 03 IPv4 Header

41. – 41 – CSCE 815 Sp 03 IPv6 Header

42. – 42 – CSCE 815 Sp 03 IP Security Overview IPSec is not a single protocol. Instead, IPSec provides a set of security algorithms plus a general framework that allows a pair of communicating entities to use whichever algorithms provide security appropriate for the communication. IPSec is not a single protocol. Instead, IPSec provides a set of security algorithms plus a general framework that allows a pair of communicating entities to use whichever algorithms provide security appropriate for the communication.

43. – 43 – CSCE 815 Sp 03 IP Security Overview Applications of IPSec Secure branch office connectivity over the Internet Secure remote access over the Internet Establsihing extranet and intranet connectivity with partners Enhancing electronic commerce security

44. – 44 – CSCE 815 Sp 03 IP Security Scenario

45. – 45 – CSCE 815 Sp 03 IP Security Overview Benefits of IPSec Transparent to applications (below transport layer (TCP, UDP) Provide security for individual users IPSec can assure that: A router or neighbor advertisement comes from an authorized router A redirect message comes from the router to which the initial packet was sent A routing update is not forged

46. – 46 – CSCE 815 Sp 03 IP Security Architecture IPSec documents: RFC 2401: An overview of security architecture RFC 2402: Description of a packet encryption extension to IPv4 and IPv6 RFC 2406: Description of a packet emcryption extension to IPv4 and IPv6 RFC 2408: Specification of key managament capabilities

47. – 47 – CSCE 815 Sp 03 IPSec Document Overview

48. – 48 – CSCE 815 Sp 03 IPSec Services Access Control Connectionless integrity Data origin authentication Rejection of replayed packets Confidentiality (encryption) Limited traffic flow confidentiallity

49. – 49 – CSCE 815 Sp 03 Recommended Reading Comer, D. Internetworking with TCP/IP, Volume I: Principles, Protocols and Architecture. Prentic Hall, 1995 Stevens, W. TCP/IP Illustrated, Volume 1: The Protocols. Addison-Wesley, 1994