and Cryptography Network Security
Third Edition by William Stallings Lecture slides by Lawrie Brown
Chapter 16 IP Security
If a secret piece of news is divulged by a spy before the time is ripe, he must be put to death, together with the man to whom the secret was told. --The Art of War, Sun Tzu
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
IPSec
general IP Security mechanisms provides
authentication confidentiality key management
applicable to use over LANs, across public & private WANs, & for the Internet
IPSec Uses
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
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
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
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
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
on based use of a MAC
HMAC-MD5-96 or HMAC-SHA-1-96
parties must share a secret key
Authentication Header
Transport & Tunnel Modes
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
Encapsulating Security Payload
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
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)
Combining Security Associations
Key Management
handles key generation & distribution typically need 2 pairs of keys
2 per direction for AH & ESP
manual key management
sysadmin manu...