ip security ge zhang [email protected]. packet-switched network is not secure! the protocols were...
TRANSCRIPT
Packet-switched network is not Secure!
• The protocols were designed in the late 70s to early 80s– Very small network (closed environment)
• All hosts are assumed to be trusted• So are the users• Therefore, security was not an issue
Message transfer over the Internet
Alice Bob
Untrusted
OSI security architecture
• Security attacks: any action that compromises the security of information.
• Security mechanism: A method that is designed to detect, prevent or recover from a security attack
• Security service: A service that enhances the security of a system
Scenario
Alice BobAttacker
Passive attacks
Alice Bob
Attacker
Read contents of message
from Alice to Bob
Alice Bob
Attacker
Observe who communicated
whom
Active attacks
Alice
Attacker
Attacker disrupts service
provided by server
Alice Bob
Attacker
Message from attacker that appears to be
from Alice
Alice Bob
Attacker
Capture message from Bob to Alice;
later replay message to Alice
Alice Bob
Attacker
Attacker modifies
message from Alice to Bob
Security services
• Data origin authentication
• Data confidentiality
• Anonymity
• Data intergrity
• Non-repudiation
Security mechanism
• Encipherment
• Digital signature
• Trusted functionality
• Detection and prevention
• …
Layered TCP/IP model
• IPSec is working in IP layer• Protect IP packets
Goals of IPSec
• to verify sources of IP packets– Data source authentication
• to prevent replaying of old packets
• to protect integrity and/or confidentiality of packets– Data Integrity/Data Encryption
IPSec subprotocols
ESP AH
IKE
IPSec Security Policy
Encapsulating SecurityPayload
Authentication Header
The Internet Key Exchange
IPSec—IP Security• Provide encryption and integrity
protection to IP packets (and authentication of two peers).– AH (Authentication Header)
• An additional header, provides integrity protection
– ESP (Encapsulating Security Payload)• Also an addition header, provides encryption and
integrity protection
– IKE (Internet Key Exchange)• Establishing session keys (used for AH & ESP)
as well as authentication.
IPSec
• A collection of protocols (RFC 2401)– Authentication Header (AH)
• RFC 2402
– Encapsulating Security Payload (ESP)• RFC 2406
– Internet Key Exchange (IKE)• RFC 2409
– IP Payload Compression (IPcomp)• RFC 3137
Transport mode and tunnel mode
R1 R2
A BTunnel mode
Transport mode
A->B Payload
A->B Payload A->B PayloadR1->R2 A->B Payload
Authentication Header (AH)
• Provides source authentication– Protects against source spoofing
• Provides data integrity• Protects against replay attacks
– Use monotonically increasing sequence numbers
• NO support for confidentiality!
AH Details
• Use 32-bit increasing sequence number to avoid replay attacks
• Use cryptographically strong hash algorithms to protect data integrity (96-bit)– Use symmetric key cryptography– HMAC-SHA-96, HMAC-MD5-96
AH Protocol (transport & tunnel mode in IPv4)
IP header data (e.g., TCP, UDP segment)AH header
IP header New IP header data (e.g., TCP, UDP segment)AH header
Authenticated except for mutable fields
Authenticated except for mutable fields
IPSec Authentication Header
Encapsulating Security Payload (ESP)
• Provides most that AH offers, and
• in addition provides data confidentiality– Uses symmetric key encryption
ESP Details
• Same as AH:– Use 32-bit sequence number to counter
replaying attacks– Use integrity check algorithms
• Only in ESP:– Data confidentiality:
• Uses symmetric key encryption algorithms to encrypt packets
ESP Protocol (transport & tunnel mode in IPv4)
IP header TCP, UDP segmentESPheader
ESPtrailer
ESPauthent
.
encryptedauthenticated
IP header TCP, UDP segmentESP
headerESP
trailerESP
authent.
encryptedauthenticated
New IP header
ESP in fact puts information both before and after the protected data.For encryption, DATA, padding, padding length and next header are encrypted.For authentication, all fields are included.
IPSec ESP Format
Anti-replay service
• Sequence number (from 0 to 232-1)• The sender increments the sequence number for
each generated packet. • How to detect replayed packet?
– The receiver maintains an array with 232 units to mark which packets have been received.
– The receiver only accepts the packets with larger sequence number than the previous one.
Both are not good methods, why?
Slide window scheme
• A windows of size W (default W = 64)• N: highest √sequence number of successfully received
packets• Three cases
– Packets in the window– Packets to the right of the window– Packets to the left of the window
605958575655 666564636261 √√√√√5453√ √
A B5459
√
64
√
Security Associations (SA)• A SA is a one-way relationship between a sender and
a receiver that affords security services to the traffic carried on it.– Two ends (from one end the other end)– A SA is identified by:
• Security Parameters Index (SPI): a local identifier points to a SA
• IP destination address• Security protocol identifier: AH? Or ESP?
– SA parameters:• Sequence number counter• Anti-replay window• AH information (key, algorithms)• ESP information (key, algorithms)• IPSEc protocol mode (Tunnel, transport)• …
Internet Key Exchange Protocol
• SA could be created manually, but…
• Internet Key Exchange Protocol (IKE)– Exchange and negotiate security policies – Establish security sessions
• Identified as Security Associations
– Key exchange– Key management– Can be used outside IPsec as well
Virtual Private Networks (VPNs)
• Virtual– It is not a physically distinct network
• Private– Tunnels are encrypted to provide confidentiality
• Using VPN while traveling
Mail serverIntranet server
Tunnel
Discussion
• IPSec is not the only solution!– Security features can be added on top of IP!
• e.g. Kerberos, SSL
• Confused?– IP, IPSec protocols are very complex!
• Two modes, three sub protocols
– Complexity is the biggest enemy of security
Discussion
• Has it been used?– Yes—primarily used by some VPN
vendors• But not all routers support it
– No—it is not really an end-to-end solution• Authentication is too coarse (host based)• Default encryption algorithm too weak (DES)• Too complex for applications to use
Key points
• Security attack, mechanism and service• Classical attacks in the internet• IPSec encompasses : authentication,
confidentiality and key management• AH and ESP• Transport mode and tunnel mode• Slide window to defend against replay attack• VPN