文档介绍：Session-Level Security
PGP, ssh, S/WAN, satan & crack: Securing the
by any means necessary
— Don Kitchen
IPSEC
IP security — security built into the IP layer
Provides host-to-host (or firewall-to-firewall) encryption
and authentication
Required for IPv6, optional for IPv4
Comprised of two parts:
• IPSEC proper (authentication and encryption)
• IPSEC key management
IPSEC Architecture
Key management establishes a security association (SA)
for a session
• SA used to provide authentication/confidentiality for that
session
• SA is referenced via a security parameter index (SPI) in each
IP datagram header
AH
Authentication header — integrity protection only
Inserted into IP datagram:
AH (ctd)
Authenticates entire datagram:
Mutable fields (time-to-live, IP checksums) are zeroed
before AH is added
ESP
Encapsulating security protocol — authentication and
confidentiality
Inserted into IP datagram:
ESP (ctd)
Secures data payload in datagram:
Encryption protects payload
• Authentication protects header and encryption
IPSEC Algorithms
DES for encryption
HMAC/MD5 and SHA for authentication
Others optional
Processing
Use SPI to look up security association (SA)
Perform authentication check using SA
Perform decryption of authenticated data using SA
Operates in two modes
• Transport mode (secure IP)
• Tunneling mode (secure IP inside standard IP)
IPSEC Key Management
ISAKMP
• Security Association and Key Management Protocol
Oakley
• DH-based key management protocol
Photuris
• DH-based key management protocol
SKIP
• Sun’s DH-based key management protocol
Protocols changed considerably over time, most borrowed
ideas from each other
Photuris
Latin for “firefly”, Firefly is the NSA’s key exchange
protocol for STU-III secure phones
Three-stage protocol
1. Exchange cookies
2. Use DH to establish a shared secret
Agree on security parameters
3. Identify other party
Authenticate data exchanged in step