IPS

ec and VP

N

INF

O 404 –

Lecture 1706/05/2009

Protecting D

ata with IP

Sec (1)

•IP

Sec

–S

tands for Internet Protocol S

ecurity •

For IP

v4 and IPv6 ⇨

Netw

ork layer –

Provides authentication and encryption of data

–P

rovides authentication and encryption of data across IP

-based networks

–A

security framew

ork that allows secure

comm

unication between 2 entities using

appropriate algorithms

–M

anages and secures authentication, authorization, confidentiality, packet anti-replay

7 –A

pplication

6 –P

resentationA

pplication

5-

Session

4 -Transport

Transport

3 -N

etwork

←

IPS

ec →Internetw

ork

IPS

ec in OS

I Reference M

odel (left) vs. TC

P/IP

M

odel (right)

←

IPS

ec →

2 -D

ata LinkN

etwork Interface

1 -P

hysical

Protecting D

ata with IP

Sec (2)

•IP

Security (IP

Sec)

to avoid unauthorized captured data–

Com

promising keys: shared key

–S

poofing: IP @

, packet sequence numbers,

other personal information to create new

other personal inform

ation to create new

packets appear coming from

actual user com

puter–

Modifying

data–

Attacking

applications: attackers add own

software to packets and use packets to

introduce software into destination com

puter

Protecting D

ata with IP

Sec (3)

•D

igitally signingand encrypting

data before transm

ission•

IPS

ec encrypts the information in IP

datagrams

by encapsulating

it so that even if the packets are captured, none of the data inside can be readcaptured, none of the data inside can be read

•IP

based-protocol, it provides end-to-end encryption

•Interm

ediatesystem

s, such as routers, treat the encrypted partof the packets purely as payload

•P

rotocols besides IPS

ec, such as SS

L or TLS

, application-layer protocols that can encrypt only specific types of traffic (W

eb)

IPS

ecS

ervices (1)

–IE

TF

(Internet Engineering T

ask Force )

security architecture & a set of protocols (see

references) and algorithms that provide

security services for IP traffic

•S

ecurity protocols : Authentication H

eader &

Encapsulating S

ecurity Payload

•S

ecurity Associations

•K

ey Managem

ent Service

•A

uthentication and encryption algorithms

IPS

ecS

ervices (2)

•A

uthentication Header (A

H)

–E

stablishes identity of the message sender

and ensures that the transmitted data has not

been tampered w

ithbeen tam

pered with

–E

ncapsulating Security P

ayload (ES

P)

•S

ame as A

H +

defines data encryption methods

IPS

ecS

ervices (3)

•S

ecurity Association

–C

ontract or negotiation between 2

comm

unicating entities defining security param

eters to use during IPS

ec param

eters to use during IPS

ec com

munication

•C

iphering algorithms &

IPS

ec protocols•

Keys &

key validity•

…

–O

ne way =

Sim

plex

IPS

ecS

ervices (4)

•K

ey Managem

ent Service

–U

sually Internet Key E

xchange (IKE

) securely establishes and passes shared keys betw

een sitesbetw

een sites–

Keys can also be passed m

anually

IPS

ecA

rchitecture

Takenfrom

: http://technet.m

icrosoft.com/en-us/library/bb726946

.aspx

IPS

ecA

pplication

•U

sed for LAN

s, WA

Ns, Internet

–U

sed to build secure tunnel over open netw

ork such as Virtual P

rivate Netw

ork (V

PN

s)(V

PN

s)–

Branch office connectivity

–R

emote access

–C

onnectivity with partners: Intranet

•U

sually in border routers and/or firewalls

IPS

ec Functions (1)

•K

ey generation–

2 C both m

ust access to shared encryption key: D

iffie–Hellm

analgorithm

to compute shared key

•C

ryptographic checksums

–cryptographic keys to calculate checksum

for –

cryptographic keys to calculate checksum for

data in each packet, called a Hash M

essage A

uthentication Code

(HM

AC

)–

HM

AC

in combination w

ith Message D

igest 5(M

D5) and H

MA

C in com

bination with S

ecure H

ash Algorithm

-1(S

HA

1): •

SH

A1 160-bit key and M

D5 128-bit key

•S

HA

1 in US

A for high-level security requirem

ent

IPS

ec Functions (2)

•M

utual authentication–

C authenticate e/o to establish a trust relationship

–K

erberos in Window

s, digital certificates, or pre-shared key

•R

eplay prevention•

Replay prevention

–R

eplay even when data in packets is encrypted

–IP

Sec prevents replay by assigning a sequence

number to each packet: anti-replay services

•IP

packet filtering–

IPS

ec includes its own packet filtering m

echanism:

prevent DoS

attacks: port, @, protocol

Detail of A

H and E

SP

Protocols (1)

•T

wo protocols that provide different types

of security for network com

munications

–IP

Authentication H

eader(A

H)

–IP

Encapsulating S

ecurity Payload

(ES

P)

–IP

Encapsulating S

ecurity Payload

(ES

P)

Detail of A

H and E

SP

Protocols (2)

IP A

uthentication Header

(AH

)•

Does not encrypt the data in IP

packets, but it does provide authentication, anti-replay, and integrity servicesreplay, and integrity services

•A

H by itself or in com

bination with E

SP

•A

H alone provides basic security services,

with relatively low

overhead

Detail of A

H and E

SP

Protocols (3)

IP A

uthentication Header

Detail of A

H and E

SP

Protocols (4)

•N

ext Header

–code specifying the protocol that generated header im

mediately follow

ing the A

H header,

–codes specified by the Internet A

ssigned Num

bers Authority ( IA

NA

).–

IPS

ec is using AH

alone, this field contains the code for the protocol that generated the datagram

’s payload. Which ones?

•P

ayload LengthS

pecifies the length of the AH

header•

Reserved U

nused•

Reserved U

nused•

Security P

arameters Index

–defines the datagram

’s security association = a list of security m

easures, negotiated by the com

municating C

s•

Sequence N

umber

–form

1 in first packet using a particular security association, and increm

ented by 1 in every subsequent packet using the same security

association–

the same sequence num

bers are discarded•

Authentication D

ata–

integrity check value (ICV

) that the sending computer calculates, based

on selected IP header fields, the A

H header, and the datagram

’s IP

payload

Detail of A

H and E

SP

Protocols (5)

IP E

ncapsulating Security P

ayload(E

SP

)•

Actually encrypts the data in an IP

datagram

•E

SP

also provides authentication, integrity, •

ES

P also provides authentication, integrity,

and anti-replay services•

Inserts header and trailer, surround the datagram

’s payload: encrypts all data follow

ing the ES

P header, up to and

including ES

P trailer

Detail of A

H and E

SP

Protocols (6)

ES

P•

By itself or in com

bination with A

H•

Maxim

um possible security for a data

transmission

transmission

•IC

V, it calculates the value only on the

information betw

een the ES

P header and

trailer; no IP header fields

Detail of A

H and E

SP

Protocols (7)

IP E

ncapsulating Security P

ayload

Detail of A

H and E

SP

Protocols (8)

Security P

arameters Index

–value that com

bine packet’s destination IP @

and its security protocol (AH

or ES

P),

defines datagram’s security association.

Sequence N

umber

–value that starts at 1 in the first packet using a particular security association, and is increm

ented by 1 in every subsequent packet using the same security association.

–D

uplicates are discardedP

ayload Data

–C

ontains TC

P, U

DP

, or ICM

P inform

ation carried inside the original IP datagram

–C

ontains TC

P, U

DP

, or ICM

P inform

ation carried inside the original IP datagram

Padding

–added to P

ayload Data field to ensure P

ayload Data has a boundary required by the

encryption algorithmP

ad Length–

Specifies the num

ber of bytes of padding the system added to the P

ayload Data field to

fill out 32-bit word

Next H

eader –

code specifying the protocol generated the header imm

ediately following the E

SP

header, specified by IA

NA

–A

lmost all cases, code for the protocol that generated the datagram

’s payload: which

ones?A

uthentication Data

–IC

V based on the inform

ation after the ES

P header, up to and including the E

SP

trailer.

Transport M

ode (1)

•T

ransport Mode: protect com

munications

between com

puters on NW

–T

wo end system

s must support IP

Sec but

intermediate system

s (such as routers) need interm

ediate systems (such as routers) need

not–

All of A

H and E

SP

protocols applies to transport m

ode

Transport M

ode (2)

Takenfrom

: http://technet.m

icrosoft.com/en-us/library/bb726946

.aspx#EC

AA

Tunnel M

ode (1)

•T

unnel mode designed provide security for W

AN

connections–

particularly Virtual P

rivate Netw

ork(V

PN

) connections, via the Internet as a com

munications m

edium–

tunnel mode connection, end system

s do not support and implem

ent the IP

Sec protocols

–B

ut routers at both ends of the WA

N connection

–B

ut routers at both ends of the WA

N connection

–T

he tunnel mode com

munications process proceeds as follow

s:

1.C

on one of PN

transmit data using standard, unprotected IP

datagrams

2.P

ackets reach router that provides access to WA

N, encapsulates using

IPS

ec, encrypting and hashing data3.

Router transm

its encapsulated packets to destination router at end of the W

AN

connection4.

Destination router verifies packets by calculating and com

paring ICV

s, and decrypts it if necessary

5.D

estination router repackages information in packet into standard,

unprotected IP datagram

s and transmits to destination(s) on P

N

Tunnel M

ode (2)

•IP

Sec uses a different packet structure in

tunnel mode

–C

reate entirely new datagram

and use it to encapsulate the existing datagram

.encapsulate the existing datagram

.–

Original datagram

, inside new datagram

, rem

ains unchanged. The IP

Sec headers are

part of the outer datagram, w

hich exists only to get the inner datagram

from one router to

the other.Tunnel M

ode (3)

Takenfrom

: http://technet.m

icrosoft.com/enus/library/bb726946.

aspx#EC

AA

Virtual P

rivate Netw

ork (1)•

VP

N objectives

–S

ecurity•

End-to-end security (authentication and, optionally, privacy) for host

connecting to a private network over untrusted public interm

ediate N

Ws

•S

ecurity for private NW

-to-NW

comm

unication over un-trusted interm

ediate NW

sinterm

ediate NW

s

–C

onnectivity: authorized sites, new users, m

obile users

–S

implicity and cost effective: transparency for user, sim

ple for use of application via V

PN

–Q

uality: Can provide Q

oS via S

LAs

•V

PN

basic functions–

Mem

bership discovery (identity, authorization)

–E

stablishment of secure tunnel (path) in netw

ork

Virtual P

rivate Netw

ork (2)

•T

unnelling–

encapsulating data of one protocol inside the data field of another protocol at:

–layer 2 (E

thernet @ across LA

N): P

ortion of VP

N connecting

internal sites (Intranet)–

layer 3 (routers for IP inform

ation): Portion of V

PN

connecting –

layer 3 (routers for IP inform

ation): Portion of V

PN

connecting external sites (E

xtranet)

–P

oint-to-Point T

unneling Protocol(P

PT

P)

•P

PP

for tuneling IP and non-IP

packets

–Layer 2 T

unneling Protocol(L2T

P)

•M

erge PP

TP

and the Layer 2 Forw

arding Protocol (L2F

P)

•IP

and non-IP packets over IP

NW

–IP

Security

(IPS

ec)

Different V

PN

s (1)

•T

wo types

–R

emote-A

ccess–

Site-to-S

ite

29

Different V

PN

s (2)

••R

emote

Rem

ote--Access

Access

–U

se the local dialup infrastructures of Internet S

ervice Providers. A

llows m

obile workers to

take advantage of broadband connectivity

30

take advantage of broadband connectivity and secure rem

ote comm

unication

Different V

PN

s (3)••

Site

Site--toto--S

iteS

ite–

Alternative to W

AN

infrastructure to connect branch offices, hom

e offices, or business partners' sites to all or portions of a com

pany's network

31

company's netw

ork–

WA

N requirem

ents-(multiple protocols, high

reliability, and extensive scalability—but)

more cost-effectively and m

ore flexible–

Public Internet or IS

P netw

orks

Rem

ote-Access and S

ite-to-Site

VP

N (4)

32Taken from: http://computer.howstuffworks.com/vpn3.htm

Advantages of V

PN

•Inexpensive alternative to W

AN

over leased lines

•P

rovide security support––

privacyprivacy

over the Internet.

33 ––encapsulateencapsulate

different insecure protocols: IP, 802.1

•E

asy to use–

Mobile user should understand protocol ->

transparent S

SH

tunnel with an internal IP

address

•R

esource consolidation

Disadvantage of V

PN

•N

eed time and expertise for setup

•D

ifficult to troubleshoot•

Sm

all performance overhead

–encapslation/decapsulation

34

–encapslation/decapsulation

•V

PN

Interoperability

Security provided by V

PN

•C

onfidentiality, Integrity, Authenticity

•E

ncryption to secure comm

unications–

IPS

ec–

SS

H

35

–S

SH

–O

ther

•S

ecurity depends on underlying protocols

Design C

hoice

•H

ardware vs. S

oftware

•A

ll hardware

•A

ll software

•B

oth

•E

xamples

36 •E

xamples

–G

ateway to gatew

ay–

Softw

are (end user) to gateway

VP

N C

onfiguration: SS

H over P

PP

(1)

•P

oint-to-Point P

rotocol over Secure S

hellS

ecure Shell

–S

SH

connection client to server–

PP

P daem

ons comm

unicates through SS

H

37VP

N C

onfiguration: SS

L over PP

P

(2)•

Point-to-P

oint Protocol over S

ecure S

ocket Layer••

Secure S

ocket LayerS

ecure Socket Layer

(SS

LS

SL)

–H

ost Authentication +

Certification

38

–H

ost Authentication +

Certification

VP

N C

onfiguration: SS

L over PP

P

(3)•

Initial Handshake

–“H

ello”: SS

L Version, C

ipher choices, …

•S

ession Key determ

ined •

SS

L Connection established

39 •S

SL C

onnection established–

Data transferred over P

PP

VP

N C

onfiguration: Other (4)

•V

ia Concentrator

–A

ccepts connections from V

PN

peer concentrator

–S

uppress overhead in gateways

40

–S

uppress overhead in gateways

••Layer 2 T

unneling Protocol

Layer 2 Tunneling P

rotocol(L2TP

L2TP

)–

If supported by router–

Often com

bined with IP

Sec for highest security

References

1.R

FC

2401: Security A

rchitecture for the Internet Protocol

:http://ww

w.ietf.org/rfc/rfc2401.txt

2.R

FC

2402: IP A

uthentication Header

3.R

FC

2406: IP E

ncapsulating Security P

ayload (ES

P)

4.R

FC

2408: Internet Security A

ssociation and Key

4.R

FC

2408: Internet Security A

ssociation and Key

Managem

ent Protocol (IS

AK

MP

) 5.

RF

C 2409: T

he Internet Key E

xchange (IKE

)6.

http://technet.microsoft.com

/en-us/library/bb726946.aspx#E

CA

A7.

http://ww

w.tldp.org/H

OW

TO

/VP

N-H

OW

TO

/8.

http://ww

w.cisco.com

/en/US

/tech/tk583/tk372/technologies_tech_note09186a0080094865.shtm

l