IPSEC
Protocols
Encryption Algorithms
packetlife.net
Internet Security Association and Key Management
Protocol (ISAKMP)
A framework for the negotiation and management of
security associations between peers (traverses UDP/500)
Internet Key Exchange (IKE)
Responsible for key agreement using asymmetric
cryptography
Encapsulating Security Payload (ESP)
Provides data encryption, data integrity, and peer
authentication; IP protocol 50
Authentication Header (AH)
Provides data integrity and peer authentication, but not data
encryption; IP protocol 51
IPsec Modes
TCP/UDP
ESP/AH
TCP/UDP
L2
L2
IP
IP
L2
Publicité
New IP
ESP/AH
IP
TCP/UDP
Original
Packet
Transport
Mode
Tunnel
Mode
Transport Mode
The ESP or AH header is inserted behind the IP header; the
IP header can be authenticated but not encrypted
Tunnel Mode
A new IP header is created in place of the original; this
allows for encryption of the entire original packet
Configuration
crypto isakmp policy 10
encryption aes 256
hash sha
authentication pre-share
group 2
lifetime 3600
ISAKMP Policy
crypto isakmp key 1 MySecretKey address 10.0.0.2
ISAKMP Pre-Shared Key
Publicité
IPsec Transform Set
crypto ipsec transform-set MyTS esp-aes 256 esp-sha-hmac
mode tunnel
IPsec Profile
crypto ipsec profile MyProfile
set transform-set MyTS
interface Tunnel0
Virtual Tunnel Interface
ip address 172.16.0.1 255.255.255.252
tunnel source 10.0.0.1
tunnel destination 10.0.0.2
tunnel mode ipsec ipv4
tunnel protection ipsec profile MyProfile
Type
Key Length (Bits)
Strength
DES Symmetric
56
3DES Symmetric
168
Weak
Medium
AES Symmetric
128/192/256
Strong
RSA Asymmetric
Publicité
1024+
Strong
Hashing Algorithms
Length (Bits)
MD5 128
SHA-1 160
Strength
Medium
Strong
IKE Phases
Phase 1
A bidirectional ISAKMP SA is established
between peers to provide a secure management
channel (IKE in main or aggressive mode)
Phase 1.5 (optional)
Xauth can optionally be implemented to enforce
user authentication
Phase 2
Two unidirectional IPsec SAs are established for
data transfer using separate keys (IKE quick
mode)
Terminology
Data Integrity
Secure hashing (HMAC) is used to ensure data
has not been altered in transit
Data Confidentiality
Publicité
Encryption is used to ensure data cannot be
intercepted by a third party
Data Origin Authentication
Authentication of the SA peer
Anti-replay
Sequence numbers are used to detect and
discard duplicate packets
Hash Message Authentication Code (HMAC)
A hash of the data and secret key used to
provide message authenticity
Diffie-Hellman Exchange
A shared secret key is established over an
insecure path using public and private keys
Troubleshooting
show crypto isakmp sa
show crypto isakmp policy
show crypto ipsec sa
show crypto ipsec transform-set
debug crypto {isakmp | ipsec}
by Jeremy Stretch
v2.0