ipsec internet security in network and system.ppt

network security

1. IP Security

2. IP Security

Have a range of application specific Have a range of application specific
security mechanismssecurity mechanisms

eg. S/MIME, PGP, Kerberos, SSL/HTTPSeg. S/MIME, PGP, Kerberos, SSL/HTTPS

However there are security concerns that However there are security concerns that
cut across protocol layerscut across protocol layers

Would like security implemented by the Would like security implemented by the
network for all applicationsnetwork for all applications

3. IPSec

General IP Security mechanismsGeneral IP Security mechanisms

ProvidesProvides

authenticationauthentication

confidentialityconfidentiality

key managementkey management

Applicable to use over LANs, across public Applicable to use over LANs, across public
& private WANs, & for the Internet& private WANs, & for the Internet

4. IPSec Uses

5. Benefits of IPSec
In a firewall/router provides strong security to In a firewall/router provides strong security to
all traffic crossing the perimeterall traffic crossing the perimeter
In a firewall/router is resistant to bypassIn a firewall/router is 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 usersCan provide security for individual users
Secures routing architectureSecures routing architecture

6. IP Security Architecture

Specification is quite complexSpecification is quite complex

Defined in numerous RFC’sDefined in numerous RFC’s

incl. RFC 2401/2402/2406/2408incl. RFC 2401/2402/2406/2408

many others, grouped by categorymany others, grouped by category

Mandatory in IPv6, optional in IPv4Mandatory in IPv6, optional in IPv4

Have two security header extensions:Have two security header extensions:

Authentication Header (AH)Authentication Header (AH)

Encapsulating Security Payload (ESP)Encapsulating Security Payload (ESP)

7. Architecture & Concepts

Tunnel vs. Transport modeTunnel vs. Transport mode

Security association (SA)Security association (SA)

Security parameter index (SPI)Security parameter index (SPI)

Security policy database (SPD)Security policy database (SPD)

SA database (SAD)SA database (SAD)

Authentication header (AH)Authentication header (AH)

Encapsulating security payload (ESP)Encapsulating security payload (ESP)

Practical Issues w/ NATPractical Issues w/ NAT

8. A B
Encrypted Tunnel
Gateway 1 Gateway 2
New IP
Header
AH or ESP
Header
TCPDataOrig IP
Header
Encrypted
Unencrypted
Unencrypted
Transport Mode vs. Tunnel Mode

Transport mode: host -> hostTransport mode: host -> host

Tunnel mode: host->gateway or gateway->gatewayTunnel mode: host->gateway or gateway->gateway

9. Transport Mode
ESP protects higher layer payload onlyESP protects higher layer payload only

AH can protect IP headers as well as higher AH can protect IP headers as well as higher
layer payloadlayer payload
IP
header
IP
options
IPSec
header
Higher
layer protocol
ESP
AH
Real IP
destination

10. Tunnel Mode

ESP applies only to the tunneled packetESP applies only to the tunneled packet
AH can be applied to portions of the outer AH can be applied to portions of the outer
headerheader
Outer IP
header
Inner IP
header
IPSec
header
Higher
layer protocol
ESP
AH
Real IP destinationDestination
IPSec
entity

11. Security Association - SA

Defined by 3 parameters:Defined by 3 parameters:

Security Parameters Index (SPI)Security Parameters Index (SPI)

IP Destination AddressIP Destination Address

Security Protocol IdentifierSecurity Protocol Identifier

Have a database of Security Associations Have a database of Security Associations

Determine IPSec processing for sendersDetermine IPSec processing for senders

Determine IPSec decoding for destinationDetermine IPSec decoding for destination

SAs are not fixed! Generated and customized per SAs are not fixed! Generated and customized per
traffic flowstraffic flows

12. Security Parameters Index - SPI

Can be up to 32 bits largeCan be up to 32 bits large

The SPI allows the destination to select the The SPI allows the destination to select the
correct SA under which the received packet correct SA under which the received packet
will be processed will be processed

According to the agreement with the senderAccording to the agreement with the sender

The SPI is sent with the packet by the senderThe SPI is sent with the packet by the sender

SPI + Dest IP address + IPSec Protocol (AH or SPI + Dest IP address + IPSec Protocol (AH or
ESP) uniquely identifies a SAESP) uniquely identifies a SA

13. SA Database - SAD

Holds parameters for each SAHolds parameters for each SA

Lifetime of this SALifetime of this SA

AH and ESP informationAH and ESP information

Tunnel or transport modeTunnel or transport mode

Every host or gateway participating in Every host or gateway participating in
IPSec has their own SA databaseIPSec has their own SA database

14. Security Policy Database - SPD

What traffic to protect?What traffic to protect?

Policy entries define which SA or SA Policy entries define which SA or SA
bundles to use on IP trafficbundles to use on IP traffic

Each host or gateway has their own SPDEach host or gateway has their own SPD

Index into SPD by Selector fieldsIndex into SPD by Selector fields

Dest IP, Source IP, Transport Protocol, IPSec Dest IP, Source IP, Transport Protocol, IPSec
Protocol, Source & Dest Ports, …Protocol, Source & Dest Ports, …

15. SPD Entry Actions
DiscardDiscard
Do not let in or outDo not let in or out

BypassBypass

Outbound: do not apply IPSecOutbound: do not apply IPSec
Inbound: do not expect IPSecInbound: do not expect IPSec

Protect – will point to an SA or SA bundleProtect – will point to an SA or SA bundle

Outbound: apply securityOutbound: apply security
Inbound: check that security must have been Inbound: check that security must have been
appliedapplied

16. SPD Protect Action

If the SA does not exist…If the SA does not exist…

Outbound processing: use IKE to generate SA Outbound processing: use IKE to generate SA
dynamicallydynamically

Inbound processing: drop packetInbound processing: drop packet

17. Is it for IPSec?
If so, which policy
entry to select?
…
SPD
(Policy)
…
SA
Database
IP Packet
Outbound packet (on A)
A B
SPI & IPSec
Packet
Send to B
Determine the SA
and its SPI
IPSec processing
Outbound Processing

18. Use SPI to
index the SAD
…
SA Database
Original IP Packet
SPI & Packet
Inbound packet (on B) A B
From A
Inbound Processing
…
SPD
(Policy)
Was packet properly
secured?
“un-process”

19. Architecture & Concepts

Tunnel vs. Transport modeTunnel vs. Transport mode

Security association (SA)Security association (SA)

Security parameter index (SPI)Security parameter index (SPI)

Security policy database (SPD)Security policy database (SPD)

SA database (SAD)SA database (SAD)

Authentication header (AH)Authentication header (AH)

Encapsulating security payload (ESP)Encapsulating security payload (ESP)

Practical Issues w/ NATPractical Issues w/ NAT

20. Authenticated Header

Data integrityData integrity

Entire packet has not been tampered withEntire packet has not been tampered with

AuthenticationAuthentication

Can “trust” IP address sourceCan “trust” IP address source

Use MAC to authenticateUse MAC to authenticate

Symmetric encryption, e.g, DESSymmetric encryption, e.g, DES

One-way hash functions, e.g, HMAC-MD5-96 or HMAC-One-way hash functions, e.g, HMAC-MD5-96 or HMAC-
SHA-1-96SHA-1-96

Anti-replay featureAnti-replay feature

Integrity check valueIntegrity check value

21. ……
SAD
SPI
Sequence Number
ICV
Next Header
(TCP/UDP)
Payload Length
Reserved
IPSec Authenticated Header
Length of the authentication headerLength of the authentication header

22. Integrity Check Value - ICV

Keyed Message authentication code (MAC) Keyed Message authentication code (MAC)
calculated overcalculated over

IP header field that do not change or are predictableIP header field that do not change or are predictable

Source IP address, destination IP, header length, etc.Source IP address, destination IP, header length, etc.

Prevent spoofingPrevent spoofing

Mutable fields excluded: e.g., time-to-live (TTL), IP Mutable fields excluded: e.g., time-to-live (TTL), IP
header checksum, etc.header checksum, etc.

IPSec protocol header except the ICV value fieldIPSec protocol header except the ICV value field

Upper-level dataUpper-level data

Code may be truncated to first 96 bitsCode may be truncated to first 96 bits

23. AH: Tunnel and Transport Mode

OriginalOriginal

Transport ModeTransport Mode

Cover most of the Cover most of the
original packetoriginal packet

Tunnel ModeTunnel Mode

Cover entire Cover entire
original packetoriginal packet

24. Encapsulating Security Payload (ESP)

Provide Provide message content confidentialitymessage content confidentiality

ProvideProvide limited traffic flow confidentiality limited traffic flow confidentiality

Can optionally Can optionally provide the same authentication provide the same authentication
services as AHservices as AH

Supports range of ciphers, modes, paddingSupports range of ciphers, modes, padding

Incl. DES, Triple-DES, RC5, IDEA, CAST etcIncl. DES, Triple-DES, RC5, IDEA, CAST etc

A variant of DES most commonA variant of DES most common

Pad to meet blocksize, for traffic flowPad to meet blocksize, for traffic flow

25. ESP: Tunnel and Transport Mode
OriginalOriginal
Transport ModeTransport Mode
Good for host to Good for host to
host traffichost traffic

Tunnel ModeTunnel Mode
Good for VPNs, Good for VPNs,
gateway to gateway gateway to gateway
securitysecurity

26. Outbound Packet Processing

Form ESP headerForm ESP header

Security parameter index (SPI)Security parameter index (SPI)

Sequence numberSequence number

Pad as necessaryPad as necessary

Encrypt result [payload, padding, pad length, Encrypt result [payload, padding, pad length,
next header]next header]

Apply authentication (optional)Apply authentication (optional)

Allow rapid detection of replayed/bogus packetsAllow rapid detection of replayed/bogus packets

Integrity Check Value (ICV) includes whole ESP Integrity Check Value (ICV) includes whole ESP
packet minus packet minus authentication dataauthentication data field field

27. SPI
Sequence Number
Original IP Header
Integrity Check Value
A
u
t
h
e
n
t
i
c
a
t
i
o
n

c
o
v
e
r
a
g
e
E
n
c
r
y
p
t
e
d
Payload (TCP Header and Data)
Variable Length
Pad
Length
Padding (0-255 bytes)
Next
Header
E
S
P

T
r
a
n
s
p
o
r
t

E
x
a
m
p
l
e

28. Inbound Packet Processing...
Sequence number checkingSequence number checking
Duplicates are rejected!Duplicates are rejected!
Packet decryptionPacket decryption

Decrypt quantity [ESP payload,padding,pad Decrypt quantity [ESP payload,padding,pad
length,next header] per SA specificationlength,next header] per SA specification
Processing (stripping) padding per encryption Processing (stripping) padding per encryption
algorithmalgorithm
Reconstruct the original IP datagramReconstruct the original IP datagram

Authentication verification (optional)Authentication verification (optional)
Allow potential parallel processing - decryption Allow potential parallel processing - decryption
& verifying authentication code& verifying authentication code

29. Architecture & Concepts

Tunnel vs. Transport modeTunnel vs. Transport mode

Security association (SA)Security association (SA)

Security parameter index (SPI)Security parameter index (SPI)

Security policy database (SPD)Security policy database (SPD)

SA database (SAD)SA database (SAD)

Authentication header (AH)Authentication header (AH)

Encapsulating security payload (ESP)Encapsulating security payload (ESP)

Practical Issues w/ NATPractical Issues w/ NAT

30. NATs
Network address translation = local, LAN-specific Network address translation = local, LAN-specific
address space translated to small number of globally address space translated to small number of globally
routable IP addressesroutable IP addresses

Motivation:Motivation:

Scarce address spaceScarce address space

Security: prevent unsolicited inbound requestsSecurity: prevent unsolicited inbound requests
Prevalence of NATsPrevalence of NATs

Claim: 50% of broadband users are behind NATsClaim: 50% of broadband users are behind NATs

All Linksys/D-Link/Netgear home routers are NATsAll Linksys/D-Link/Netgear home routers are NATs

31. NAT types

All use net-10/8 (10.*.*.*) or 192.168/16All use net-10/8 (10.*.*.*) or 192.168/16

Address translationAddress translation

Address-and-port translation (NAPT)Address-and-port translation (NAPT)

most common form today, still called NATmost common form today, still called NAT

one external (global) IP addressone external (global) IP address

Change IP header and TCP/UDP headersChange IP header and TCP/UDP headers

Will it work with IPSec?Will it work with IPSec?

32. NAT Example
IAP’s Point of Presence
Router with NAT
External IP: 68.40.162.3
Internal IP: 192.168.0.0
Router assigns internal
IPs to hosts on LAN :
A: 192.168.0.100
B: 192.168.0.101
C: 192.168.0.102
A B C
Messages sent between host B
to another host on the Internet
Host B original source socket:
192.168.0.101 port 1341
Host B translated socket:
68.40.162.3 port 5280

33. Backup Slides

34. Combining 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 form a security association association bundlebundle

may terminate at different or same may terminate at different or same
endpointsendpoints

combined bycombined by

transport adjacencytransport adjacency

iterated tunnelingiterated tunneling

issue of authentication & encryption order issue of authentication & encryption order

35. Combining Security Associations

36. SA Bundle

More than 1 SA can apply to a packetMore than 1 SA can apply to a packet

Example: ESP does not authenticate new IP Example: ESP does not authenticate new IP
header. How to authenticate?header. How to authenticate?

Use SA to apply ESP w/o authentication to Use SA to apply ESP w/o authentication to
original packetoriginal packet

Use 2Use 2
ndnd
SA to apply AH SA to apply AH

37. Outbound Packet Processing...

Integrity Check Value (ICV) calculationIntegrity Check Value (ICV) calculation

ICV includes whole ESP packet minus ICV includes whole ESP packet minus
authentication dataauthentication data field field

Implicit padding of ‘0’s between Implicit padding of ‘0’s between next headernext header and and
authentication dataauthentication data is used to satisfy block size is used to satisfy block size
requirement for ICV algorithmrequirement for ICV algorithm

38. Inbound Packet Processing

Sequence number checkingSequence number checking

Anti-replay is used only if authentication is Anti-replay is used only if authentication is
selectedselected

Sequence number should be the first ESP check Sequence number should be the first ESP check
on a packet upon looking up an SAon a packet upon looking up an SA

Duplicates are rejected! Duplicates are rejected!
0
Sliding Window
size >= 32
reject
Check bitmap, verify if new
verify

39. Anti-replay Feature

OptionalOptional

Information to enforce held in SA entryInformation to enforce held in SA entry

Sequence number counter - 32 bit for Sequence number counter - 32 bit for
outgoing IPSec packetsoutgoing IPSec packets

Anti-replay window Anti-replay window

32-bit 32-bit

Bit-map for detecting replayed packetsBit-map for detecting replayed packets

40. Anti-replay Sliding Window

Window should not be advanced until the Window should not be advanced until the
packet has been authenticatedpacket has been authenticated

Without authentication, malicious packets Without authentication, malicious packets
with large sequence numbers can advance with large sequence numbers can advance
window unnecessarilywindow unnecessarily

Valid packets would be dropped!Valid packets would be dropped!

41. ESP Processing - Header
Location...

Tunnel mode IPv4 and IPv6Tunnel mode IPv4 and IPv6
New
IP hdr
Orig
IP hdr
TCPData
ESP
trailer
ESP
Auth
ESP
hdr
New
ext hdr
New
IP hdr
TCPData
ESP
trailer
ESP
Auth
Orig
IP hdr
ESP
hdr
Orig
ext hdr
IPv4
IPv6

42. Key Management
Handles key generation & distributionHandles key generation & distribution

Typically need 2 pairs of keysTypically need 2 pairs of keys

2 per direction for AH & ESP2 per direction for AH & ESP
Manual key managementManual key management

Sysadmin manually configures every systemSysadmin manually configures every system
Automated key managementAutomated key management
Automated system for on demand creation of keys Automated system for on demand creation of keys
for SA’s in large systemsfor SA’s in large systems