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Internet Key Exchange (IKE) protocol vulnerability risks. Master's thesis seminar 18.5.2004 HUT, Networking Laboratory Composed by Ari Muittari at Nokia Networks Supervisor: Prof. Raimo Kantola Instructor: M.Sc. Jussi Kohonen. Contents. Background Research methods

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internet key exchange ike protocol vulnerability risks
Internet Key Exchange (IKE) protocol vulnerability risks

Master's thesis seminar 18.5.2004

HUT, Networking Laboratory

Composed by Ari Muittari at Nokia Networks

Supervisor: Prof. Raimo Kantola

Instructor: M.Sc. Jussi Kohonen

  • Background
  • Research methods
  • Network security concepts
  • IPsec and IKE protocols
  • Experimental part
  • Conclusions
  • New types of uses for the Internet are emerging and amount of IP traffic is growing; an ever increasing amount of attacks can be expected
  • Lack of security is a major hindrance to the widespread use of the Internet
  • IPsec (and IKE as its key exchange protocol) promises network level IP security
  • Attacking on IKE is presumably difficult because it has been designed to be robust
    • Few studies analyze the weaknesses of IKE
    • A couple of experimental attack programs are available (in contrast to the tool arsenal targeted to TCP/IP)

Research problem: Is it feasible to successfully attack IKE protocol?

research methods
Research methods
  • Modeling network security concepts
  • Reviewing the cryptography used, IPsec and IKE protocol
  • Analyzing the papers written of IKE weaknesses
  • Analyzing the existing IKE attack programs
  • Applying selected theoretical attack scenarios into practise by implementing them into attack programs
  • Experimenting these attacks in a test environment
network security concepts 1 2
Green circle: Security is retained inspite of the mounted attacks

Red circle: Security threats are realized by successful attacks

Attacker tries to adversely affect the information flow:

A basic model for network security concepts constructed

Helps to form a general view of the related concepts and their relations

Network security concepts 1(2)
network security concepts 2 2
Network security concepts 2(2)

Cryptographic methods are the building blocks of IPSec and IKE

  • Secret and Public key encryption
    • Provides confidentiality
  • Digital signature and hash functions, MAC (Message Authentication Code)
    • Provides integrity
  • Random numbers
    • Add unpredictability to cryptographic algorithms and protocols
    • Used for example for creating keys, nonces and cookies
  • Diffie-Hellman key exchange protocol
    • Two parties agree over an insecure channel on a shared secret
    • Shared secret is used to protect the following traffic
ipsec and ike protocols 1 2
IPsec and IKE protocols 1(2)

Internal structure of IPsec protocol suite

AH = Authentication Header

API = Application Programming Interface

DOI = Domain of Interpretation

ESP = Encapsulated Security Payload

ISAKMP = Internet Security Association

and Key Management Protocol

Oakley = Key Exchange Protocol

SA = Security Association

SAD = Security Association Database

SKEME = Secure Key Exchange Mechanism

SPD = Security Policy Database

ipsec and ike protocols 2 2
IKE SA and IPsec SA establisment

Main mode :

IPsec and IKE protocols 2(2)

Aggressive mode:

HDR = ISAKMP Header,

HDR* = Payloads are encrypted

SA = Security Association payload

KE = Key Exchange payload (Diffie-Hellman public value)

Ni, Nr = Nonce payload (of Initiator, Responder)

IDii, Idir = Identification payload

HASH_I, HASH_R = Hash payload (of Initiator, Responder)

experimental part 1 6
Experimental part 1(6)

Test network

  • Three hosts in a LAN (Local Area Network) running FreeBSD OS (operating system)
  • Hosts are operated via a switch matrix
  • Software of the IPsec hosts
    • IPsec: KAME
    • IKE: racoon
  • Software of the Attacker’s host
    • ettercap for enabling Man-in-the-middle (MITM) attacks by using ARP tables poisoning technique
    • ike-scan for discovering IKE services
    • ikeprobe for IKE packet fabrication
    • ikecrack for pre-shared key cracking
  • Installation of OS and software
  • Configuration of IPsec policies
experimental part 2 6
Experimental part 2(6)

Attacks on IKE are diverse:

  • Exploit weaknesses of a protocol or an implementation by applying various techniques
  • Active or passive, specific to an exchange (main or aggressive mode) or parameters used
  • Differ in terms of required effort and level of difficulty to implement and mount
  • The implications induced by an attack vary as do the benefits the attacker is able to gain

Categorization of demonstrated attacks

  • Discovery of IKE service
  • Denial-of-Service (DoS) attacks
  • Authentication attacks
experimental part 3 6
Experimental part 3(6)

Discovery of IKE service

  • If the attacker knows a specific IPsec implementation on the network, he can focus his effort on its known vulnerabilities
  • As IKE runs over UDP protocol, it needs a retransmission strategy:
    • Time to wait before resending the packet
    • Time to wait (delay) between subsequent packets
    • Count of packets to be resent before giving up
  • IPsec implementations tend to have an individual IKE retransmission strategy which forms a kind of pattern (fingerprint)
  • ike-scan discovers and identifies IPsec implementations:
    • A publicly available C program
    • Sends an initial main mode packet to the specified hosts
    • Collects timing information from responses
    • Matches that information against a database of the known implementation’s patterns
    • Concludes the IPsec/IKE implementation (vendor)
experimental part 4 6
Experimental part 4(6)

Denial-of-Service (DoS) attacks

  • The attacker’s aim is to disable the Responder by exploiting IKE protocol or implementation flaws
    • Force Responder to spend computing or memory resources
    • Force Responder to crash or jam by sending a malformed packet
  •, IKE packet fabrication tool
    • Largely rewritten and enhanced from the
    • Aggressive and main mode packet flooding
    • Initiates an IKE negotiation without trying to complete it
  • DoS protection means of IKE
    • Cookies (IKE fails to protect against even simple DoS attacks)
    • Discarding of malformed packets
    • Limited logging of abnormal events
experimental part 5 6
Experimental part 5(6)

DoS attacks classified according to a mechanism they effect on the IKE service

experimental part 6 6
Experimental part 6(6)

Authentication attacks

  • Cracking a weak pre-shared key
    •, IKE message parser and pre-shared key cracking tool
    • Largely rewritten and enhanced from the
    • The attacker captures the exchange by “tcpdump –nxq –s 600 > file”
    • ikecrack parses the capture file, computes needed keying material and MAC values and starts dictionary, hybrid and brute-force cracking
    • In aggressive mode only a capture of an exchange needed
    • In main mode also a MITM attack needed to forge a DH public key by using an ettercap plug-in program developed
  • Use of degenerated DH public keys
    • racoon accepts degenerated DH public keys and thus allows revealing of DH shared secret (implementation flaw)
  • IKE is a complex protocol. Security suffers from complexity
  • Attacking on IKE is feasible, although not trivial
  • Serious vulnerabilities demonstrated in various areas, including
    • Denial-of-Service
      • Resources can be exhausted (computing, memory and disk)
      • Implementation flaws (crashes and endless loops)
    • Authentication
      • Cracking a pre-shared key (aggressive and main mode)
      • MITM attacks on DH
  • It is only a matter of time when there are advanced attack tools available
  • IKE will probably remain in use for years (IKEv2 is an Internet-draft)
    • Still, IPsec is the current best practice in IP security
    • Realize the weaknesses and enforce respective countermeasures
    • Focus on security testing (traditionally inter-operation testing)

Further research

  • Test other IPsec implementations
  • Verify the robustness of the forthcoming IKEv2
  • Develop a security testing tool suite (move from Perl to C)
additional material 1 4
Additional material 1(4)

An example of a DoS attack which floods responder with expensive modular exponentiation computations in aggressive mode

  • perl –d –s 1:1:1:2 –ip –k user 99 –n user 77 –c 30000 –wait –b 8
  • racoon uses all the available processing capacity (95 % CPU usage)
  • Disk storage is exhausted at the rate of 10 Mbytes/hour
  • Virtual memory is exhausted at the rate of 30 Mbytes/hour (the memory remains reserved until racoon has been killed)
additional material 2 4
Additional material 2(4)

An example of a MITM attack (cracking a pre-shared key in main mode)

  • To decrypt the HASH_I the MITM has to know the encryption key which is derived from DH shared secret
  • MITM forges Responder’s DH public key gy to a value of which DH private key y he knows, and can compute DH shared secret (gx)y
  • g is defined to be 2, so if gy = 2 then y = 1 and DH shared secret is (gx)y = gx

Main mode exchange and a respective ettercap snapshot:

additional material 3 4
Additional material 3(4)

Diffie Hellman (DH) Key Exchange protocol

additional material 4 4
Additional material 4(4)

RFC 2409 The Internet Key Exchange (IKE)

  • IKE keying material and MACs in a pre-shared key authentication