CSCE 815 Network Security CSCE 815 Network Security Lecture 12 Lecture 12CSCE 815 Network Security CSCE 815 Network Security Lecture 12 Lecture 12

Email SecurityEmail Security

S/MIMES/MIME

February 25, 2003

– 2 – CSCE 815 Sp 03

PGP Operation – SummaryPGP Operation – Summary

– 3 – CSCE 815 Sp 03

ZIV compressionZIV compressionCompression based on recognizing repetitionsCompression based on recognizing repetitions

Based on Jacab Ziv and Abraham Lempel (Ziv-Lempel or LZ77)Based on Jacab Ziv and Abraham Lempel (Ziv-Lempel or LZ77)

<00b><27d><13d> 0r 00 00011010 1101<00b><27d><13d> 0r 00 00011010 1101

Sliding history buffer --- look-ahead bufferSliding history buffer --- look-ahead buffer

Decompression easy.Decompression easy.

– 4 – CSCE 815 Sp 03

Radix 64 ConversionRadix 64 Conversion

Table 5.9 – 6 bit Input versus character outputTable 5.9 – 6 bit Input versus character output

– 5 – CSCE 815 Sp 03

RFC 822RFC 822

Defines a format for text messages that are sent via Defines a format for text messages that are sent via emailemail

MIME is an extension for RFC 822 intended to address MIME is an extension for RFC 822 intended to address some problemssome problems

1.1. SMTP cannot handle binariesSMTP cannot handle binaries

2.2. SMTP cannot handle extended character sets of SMTP cannot handle extended character sets of specific languagesspecific languages

3.3. SMTP may reject large messagesSMTP may reject large messages

4.4. SMTP fails to handle ASCII SMTP fails to handle ASCII EBCIDIC translationsEBCIDIC translations

5.5. SMTP gateways cannot handle non textual dataSMTP gateways cannot handle non textual data

– 6 – CSCE 815 Sp 03

Multipurpose Internet Mail ExtensionsMultipurpose Internet Mail ExtensionsMIME - Adds new headers (RFC 822,2045)MIME - Adds new headers (RFC 822,2045)

MIME 5 header fieldsMIME 5 header fields MIME-version Content-Type Content-Transfer-Encoding Content-ID Content-Description

– 7 – CSCE 815 Sp 03

Content TypesContent Types

1.1. Text: Text: plain, richtext, enriched

2.2. Multipart: Multipart: mixed, parallel, parts can be analyzed in parallel digest, an electronic mail digest alternative

3.3. Message: RFC822, partial, external-bodyMessage: RFC822, partial, external-body

4.4. Application: octet-stream, postscriptApplication: octet-stream, postscript

5.5. Image: jpeg, gifImage: jpeg, gif

6.6. AudioAudio

7.7. Video: mpegVideo: mpeg

– 8 – CSCE 815 Sp 03

Content-Transfer-EncodingsContent-Transfer-Encodings

Defined RFC 1521Defined RFC 1521

1.1. 7bit – NVT ASCII, the default7bit – NVT ASCII, the default

2.2. Binary – not only non-ASCII characters, but lines Binary – not only non-ASCII characters, but lines may be longmay be long

3.3. Quoted-printable – mostly ASCII text Quoted-printable – mostly ASCII text

4.4. Base-64 (radix 64)Base-64 (radix 64)

5.5. 8bit non-ASCII have the eighth bit set8bit non-ASCII have the eighth bit set

6.6. X-token – a nonstandard encodingX-token – a nonstandard encoding

– 9 – CSCE 815 Sp 03

S/MIMES/MIME

Secure/Multipurpose Internet Mail ExtensionSecure/Multipurpose Internet Mail Extension

S/MIME will probably emerge as the industry standard.S/MIME will probably emerge as the industry standard.

PGP for personal e-mail security PGP for personal e-mail security

– 10 – CSCE 815 Sp 03

Simple Mail Transfer Protocol (SMTP, RFC 822)Simple Mail Transfer Protocol (SMTP, RFC 822)

SMTP Limitations - Can not transmit, or has a problem with: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 – CSCE 815 Sp 03

Header fields in MIMEHeader fields in MIME

MIME-Version:MIME-Version: Must be “1.0” -> RFC 2045, RFC 2046 Must be “1.0” -> RFC 2045, RFC 2046

Content-Type:Content-Type: More types being added by developers (application/word) More types being added by developers (application/word)

Content-Transfer-Encoding:Content-Transfer-Encoding: How message has been encoded (radix-64) How message has been encoded (radix-64)

Content-ID:Content-ID: Unique identifying character string. Unique identifying character string.

Content Description:Content Description: Needed when content is not readable text (e.g.,mpeg) Needed when content is not readable text (e.g.,mpeg)

– 12 – CSCE 815 Sp 03

User Agent RoleUser Agent Role

S/MIME uses Public-Key Certificates - X.509 version 3 signed by S/MIME uses Public-Key Certificates - X.509 version 3 signed by Certification AuthorityCertification Authority

Functions: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 – CSCE 815 Sp 03

User Agent RoleUser Agent Role

Example: Verisign (www.verisign.com)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 – CSCE 815 Sp 03

S/MIME FunctionsS/MIME Functions

enveloped dataenveloped data encrypted content and associated keys

signed datasigned data encoded message + signed digest

clear-signed dataclear-signed data cleartext message + encoded signed digest

signed & enveloped datasigned & enveloped data nesting of signed & encrypted entities

– 15 – CSCE 815 Sp 03

S/MIME Cryptographic AlgorithmsS/MIME Cryptographic Algorithms

hash functions: SHA-1 & MD5hash functions: SHA-1 & MD5

digital signatures: DSS & RSAdigital signatures: DSS & RSA

session key encryption: ElGamal & RSAsession key encryption: ElGamal & RSA

message encryption: Triple-DES, RC2/40 and othersmessage encryption: Triple-DES, RC2/40 and others

have a procedure to decide which algorithms to usehave a procedure to decide which algorithms to use

– 16 – CSCE 815 Sp 03

S/MIME Certificate ProcessingS/MIME Certificate Processing

S/MIME uses X.509 v3 certificatesS/MIME uses X.509 v3 certificates

managed using a hybrid of a strict X.509 CA hierarchy managed using a hybrid of a strict X.509 CA hierarchy & PGP’s web of trust& PGP’s web of trust

each client has a list of trusted CA’s certseach client has a list of trusted CA’s certs

and own public/private key pairs & certsand own public/private key pairs & certs

certificates must be signed by trusted CA’scertificates must be signed by trusted CA’s

– 17 – CSCE 815 Sp 03

Certificate AuthoritiesCertificate Authorities

have several well-known CA’shave several well-known CA’s

Verisign one of most widely usedVerisign one of most widely used

Verisign issues several types of Digital IDsVerisign issues several types of Digital IDs

with increasing levels of checks & hence trustwith 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 – CSCE 815 Sp 03

IP SecurityIP Security

have considered some application specific security have considered some application specific security mechanismsmechanisms eg. S/MIME, PGP, Kerberos, SSL/HTTPS

however there are security concerns that cut across however there are security concerns that cut across protocol layersprotocol layers

would like security implemented by the network for all would like security implemented by the network for all applicationsapplications

– 19 – CSCE 815 Sp 03

IPSecIPSec

general IP Security mechanismsgeneral IP Security mechanisms

providesprovides authentication confidentiality key management

applicable to use over LANs, across public & private applicable to use over LANs, across public & private WANs, & for the InternetWANs, & for the Internet

– 20 – CSCE 815 Sp 03

IPSec UsesIPSec Uses

– 21 – CSCE 815 Sp 03

Benefits of IPSecBenefits of IPSec

in a firewall/router provides strong security to all traffic in a firewall/router provides strong security to all traffic crossing the perimetercrossing the perimeter

is resistant to bypassis resistant to bypass

is below transport layer, hence transparent to is below transport layer, hence transparent to applicationsapplications

can be transparent to end userscan be transparent to end users

can provide security for individual users if desiredcan provide security for individual users if desired

– 22 – CSCE 815 Sp 03

IP Security ArchitectureIP Security Architecture

specification is quite complexspecification is quite complex

defined in numerous RFC’sdefined in numerous RFC’s incl. RFC 2401/2402/2406/2408 many others, grouped by category

mandatory in IPv6, optional in IPv4mandatory in IPv6, optional in IPv4

– 23 – CSCE 815 Sp 03

IPSec ServicesIPSec Services

Access controlAccess control

Connectionless integrityConnectionless integrity

Data origin authenticationData origin authentication

Rejection of replayed packetsRejection of replayed packets a form of partial sequence integrity

Confidentiality (encryption)Confidentiality (encryption)

Limited traffic flow confidentialityLimited traffic flow confidentiality

– 24 – CSCE 815 Sp 03

Security AssociationsSecurity Associations

a one-way relationship between sender & receiver that a one-way relationship between sender & receiver that affords security for traffic flowaffords security for traffic flow

defined by 3 parameters:defined by 3 parameters: Security Parameters Index (SPI) IP Destination Address Security Protocol Identifier

has a number of other parametershas a number of other parameters seq no, AH & EH info, lifetime etc

have a database of Security Associationshave a database of Security Associations

– 25 – CSCE 815 Sp 03

Authentication Header (AH)Authentication Header (AH)

provides support for data integrity & authentication of provides support for data integrity & authentication of IP packetsIP packets end system/router can authenticate user/app prevents address spoofing attacks by tracking sequence

numbers

based on use of a MACbased on use of a MAC HMAC-MD5-96 or HMAC-SHA-1-96

parties must share a secret keyparties must share a secret key

– 26 – CSCE 815 Sp 03

Authentication HeaderAuthentication Header

– 27 – CSCE 815 Sp 03

Transport & Tunnel ModesTransport & Tunnel Modes

– 28 – CSCE 815 Sp 03

Encapsulating Security Payload (ESP)Encapsulating Security Payload (ESP)

provides provides message content confidentiality & limited message content confidentiality & limited traffic flow confidentialitytraffic flow confidentiality

can optionally can optionally provide the same authentication services provide the same authentication services as AHas AH

supports range of ciphers, modes, paddingsupports range of ciphers, modes, padding incl. DES, Triple-DES, RC5, IDEA, CAST etc CBC most common pad to meet blocksize, for traffic flow

– 29 – CSCE 815 Sp 03

Encapsulating Security PayloadEncapsulating Security Payload

– 30 – CSCE 815 Sp 03

Transport vs Tunnel Mode ESPTransport vs Tunnel Mode ESP

transport mode is used to encrypt & optionally transport mode is used to encrypt & optionally authenticate IP dataauthenticate 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 packettunnel mode encrypts entire IP packet add new header for next hop good for VPNs, gateway to gateway security

– 31 – CSCE 815 Sp 03

Combining Security AssociationsCombining Security Associations

SA’s can implement either AH or ESPSA’s can implement either AH or ESP

to implement both need to combine SA’sto implement both need to combine SA’s form a security bundle

have 4 cases (see next)have 4 cases (see next)

– 32 – CSCE 815 Sp 03

Combining Security AssociationsCombining Security Associations

– 33 – CSCE 815 Sp 03

Key ManagementKey Management

handles key generation & distributionhandles key generation & distribution

typically need 2 pairs of keystypically need 2 pairs of keys 2 per direction for AH & ESP

manual key managementmanual key management sysadmin manually configures every system

automated key managementautomated key management automated system for on demand creation of keys for SA’s

in large systems has Oakley & ISAKMP elements

– 34 – CSCE 815 Sp 03

OakleyOakley

a key exchange protocola key exchange protocol

based on Diffie-Hellman key exchangebased on Diffie-Hellman key exchange

adds features to address weaknessesadds features to address weaknesses cookies, groups (global params), nonces, DH key exchange

with authentication

can use arithmetic in prime fields or elliptic curve fieldscan use arithmetic in prime fields or elliptic curve fields

– 35 – CSCE 815 Sp 03

ISAKMPISAKMP

Internet Security Association and Key Management Internet Security Association and Key Management ProtocolProtocol

provides framework for key managementprovides framework for key management

defines procedures and packet formats to establish, defines procedures and packet formats to establish, negotiate, modify, & delete SAsnegotiate, modify, & delete SAs

independent of key exchange protocol, encryption alg, independent of key exchange protocol, encryption alg, & authentication method& authentication method

– 36 – CSCE 815 Sp 03

ISAKMPISAKMP

– 37 – CSCE 815 Sp 03

SummarySummary

have considered:have considered: IPSec security framework AH ESP key management & Oakley/ISAKMP

– 38 – CSCE 815 Sp 03

Chapter 6 IP SecurityChapter 6 IP Security

Internetworking and Internet Protocols (Appendix 6A)Internetworking and Internet Protocols (Appendix 6A)

IP Security OverviewIP Security Overview

IP Security ArchitectureIP Security Architecture

Authentication HeaderAuthentication Header

Encapsulating Security PayloadEncapsulating Security Payload

Combinations of Security AssociationsCombinations of Security Associations

Key ManagementKey Management

– 39 – CSCE 815 Sp 03

TCP/IP ExampleTCP/IP Example

– 40 – CSCE 815 Sp 03

IPv4 HeaderIPv4 Header

– 41 – CSCE 815 Sp 03

IPv6 HeaderIPv6 Header

– 42 – CSCE 815 Sp 03

IP Security OverviewIP Security Overview

IPSec is not a single protocol. Instead, IPSec IPSec is not a single protocol. Instead, IPSec provides a set of security algorithms plus a provides a set of security algorithms plus a general framework that allows a pair of general framework that allows a pair of communicating entities to use whichever communicating entities to use whichever algorithms provide security appropriate for the algorithms provide security appropriate for the communication.communication.

– 43 – CSCE 815 Sp 03

IP Security OverviewIP Security Overview

Applications of IPSecApplications 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 – CSCE 815 Sp 03

IP Security ScenarioIP Security Scenario

– 45 – CSCE 815 Sp 03

IP Security OverviewIP Security Overview

Benefits of IPSecBenefits of IPSec Transparent to applications (below transport layer (TCP, UDP) Provide security for individual users

IPSec can assure that: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 – CSCE 815 Sp 03

IP Security ArchitectureIP Security Architecture

IPSec documents: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 – CSCE 815 Sp 03

IPSec Document OverviewIPSec Document Overview

– 48 – CSCE 815 Sp 03

IPSec ServicesIPSec Services

Access ControlAccess Control

Connectionless integrityConnectionless integrity

Data origin authenticationData origin authentication

Rejection of replayed packetsRejection of replayed packets

Confidentiality (encryption)Confidentiality (encryption)

Limited traffic flow confidentiallityLimited traffic flow confidentiallity

– 49 – CSCE 815 Sp 03

Recommended ReadingRecommended Reading

Comer, D. Comer, D. Internetworking with TCP/IP, Volume I: Internetworking with TCP/IP, Volume I: Principles, Protocols and ArchitecturePrinciples, Protocols and Architecture. Prentic Hall, . Prentic Hall, 19951995

Stevens, W. Stevens, W. TCP/IP Illustrated, Volume 1: The TCP/IP Illustrated, Volume 1: The ProtocolsProtocols. Addison-Wesley, 1994. Addison-Wesley, 1994