Transcript IPSec

IPSec
•Access control
•Connectionless integrity
•Data origin authentication
•Rejection of replayed packets
•Confidentiality
Sheng-Liang Song
[email protected]
IPSec
•Complexity
•Security worst “enemy”
•“best practice”
Sheng-Liang Song
[email protected]
Agenda
 IPSec Overview
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IPSec (Network Layer)
Modes (Tunnel/Transport)
Protocols (ESP/AH)
IKE (Internet Key Exchange)
IPSec Cases
 IPSec Discussion
 Q&A
Key Words
 ISAKMP (Internet Security Association
 and Key Management Protocol)
 SA (Security Associations)
 SPD (Security Policy Database)
 IKE (Internet Key Exchange)
 AH (Authentication Header)
 ESP (Encapsulating Security Payload)
 HMAC (Keyed-Hashing for Message Authentication)
 H(K XOR opad_5C, H(K XOR ipad_36, text))
IPSec (Network Layer)
 lives at the
network layer
 transparent to
applications
SSL
IPSec
application
User
transport
OS
network
link
physical
NIC
IPv4 Header Format
Mutable, predictable, Immutable
IPv6 Header Format
IPSec Modes (Tunnel and Transport)
 Transport Mode
 Tunnel Mode
 Transport Mode
IP header data
IP header ESP/AH
data
 Tunnel Mode
IP header data
new IP hdr
ESP/AH
IP header data
IPSec Protocols (ESP and AH)
 ESP (Encapsulating Security Payload)
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Integrity and confidentiality (HMAC/DES-CBC)
Integrity only by using NULL encryption
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 AH (Authentication Header)
 Integrity only
Original IP Layer
IP HDR
Data
Original IP Layer
IP HDR
Data
IPSec Authenticated session
IP HDR
AH HDR
Data
IPSec Encrypted session
IP HDR
ESP HDR
Data
Original IP Layer
IP HDR
Data
Original IP Layer
IP HDR
Data
encrypted
Original IP Layer
IP HDR
Data
IPSec Tunnel
Data
New IP HDR ESP HDR IP HDR
encrypted
Original IP Layer
IP HDR
Data
AH Format
The sender's counter is initialized to 0 when an SA is established.
AH/Transport
AH/Transport
ESP Format
The sender's counter is initialized to 0 when an SA is established.
ESP/Transport
ESP/Tunnel
IPSec Tunnels
TOS
IP header
Set TOS
IP Payload
Original IP Packet
TOS
IP header
IP Payload
Classified IP packet
TOS copy
TOS
IP new hdr
TOS
IP new hdr
New IP header built by tunnel entry point
TOS byte is copied
ESP header
IPSec packet
IP
IP Payload
Anti-Replay in IPSec
 Both ESP and AH have an anti-reply
mechanism
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based on sequence numbers
sender increment the sequence number after
each transmission
receiver optionally checks the sequence
number and rejects if it is out of window
How IPSec uses IKE
IPSec and IKE in Practice
Internal Network
Certificate
Authority
Digital Certificate
 Sets up a
keying channel
 Sets up data
channels
SA
Internal Network
Clear Text
Encrypted
ISAKMP (Internet Security Association
and Key Management Protocol)
SA (Security Associations)
SPD (Security Policy Database)
Discard,bypass IPsec, apply IPSec
(Overhead)
IPSec (IKE1 Phase1)
 Authenticated with Signatures
 Authenticated with Shared key
 Authenticated with Public Key Encryption
 Authenticated with Public Key Encryption
(Revised)
IPSec (Cases)
IPSec Case1
IPSec Case2
IPSec Case3
IPSec Case4
IPSec Discussion
1. IPSec authenticates machines, not users
2. Does not stop denial of service attacks
1.
Easier to do DoS
3. Order of operations:
Encryption/Authentication
4.Q & A
Reference
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Information Security: Principles and Practice, Mark
Stamp, Jan 29,2005
http://www.ietf.org/
Cisco IOS IPsec www.cisco.com/go/ipsec/
Cisco White Paper, IPsec,
http://www.cisco.com/warp/public/cc/so/neso/sqso/e
qso/ipsec_wp.htm
N. Ferguson and B. Schneier, A Cryptographic
Evaluation of IPsec, http://www.schneier.com/paperipsec.html
IPsec, Security for the Internet Protocol,
http://www.freeswan.org/freeswan_trees/freeswan2.06/doc/intro.html