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CSCE 815 Network Security Lecture 12

CSCE 815 Network Security Lecture 12. Email Security S/MIME. February 25, 2003. PGP Operation – Summary. ZIV compression. Compression based on recognizing repetitions Based on Jacab Ziv and Abraham Lempel (Ziv-Lempel or LZ77) <00b><27d><13d> 0r 00 00011010 1101

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CSCE 815 Network Security Lecture 12

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

  2. PGP Operation – Summary

  3. ZIV compression • Compression based on recognizing repetitions • Based on Jacab Ziv and Abraham Lempel (Ziv-Lempel or LZ77) • <00b><27d><13d> 0r 00 00011010 1101 • Sliding history buffer --- look-ahead buffer • Decompression easy.

  4. Radix 64 Conversion • Table 5.9 – 6 bit Input versus character output

  5. 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. 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. 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. 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. S/MIME • Secure/Multipurpose Internet Mail Extension • S/MIME will probably emerge as the industry standard. • PGP for personal e-mail security

  10. 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. 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-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. 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. 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. 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. 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. 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. 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 Class Identity Checks Usage 1 name/email check web browsing/email 2+ enroll/addr check email, subs, s/w validate 3+ ID documents e-banking/service access

  18. 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. IPSec • general IP Security mechanisms • provides • authentication • confidentiality • key management • applicable to use over LANs, across public & private WANs, & for the Internet

  20. IPSec Uses

  21. 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. 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. 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. 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. 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. Authentication Header

  27. Transport & Tunnel Modes

  28. 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. Encapsulating Security Payload

  30. 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. 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. Combining Security Associations

  33. 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. 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. 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. ISAKMP

  37. Summary • have considered: • IPSec security framework • AH • ESP • key management & Oakley/ISAKMP

  38. 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. TCP/IP Example

  40. IPv4 Header

  41. IPv6 Header

  42. 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.

  43. 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. IP Security Scenario

  45. 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. 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. IPSec Document Overview

  48. IPSec Services • Access Control • Connectionless integrity • Data origin authentication • Rejection of replayed packets • Confidentiality (encryption) • Limited traffic flow confidentiallity

  49. 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

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