ISA 662

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ISA 662 IKE Key management for IPSEC
Prof. Ravi Sandhu
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INTERNET KEY EXCHANGE(IKE)

• Hybrid protocol

IKE
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ISAKMP

• Internet security association and key management
  protocol
• separates key management from key exchanges
• complex general protocol used in a specific way
  in IKE
• can apply to protocols other than IPSEC
• for IPSEC uses UDP over IP

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IKE

• ISAKMP phase 1 establishes ISAKMP SA
• Main mode (DH with identity protection)
• Aggressive mode (DH without identity protection)
• Between phases
• New group mode
• ISAKMP phase 2 establishes SA for target
  protocol
• Quick mode

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DIFFIE-HELLMANKEY ESTABLISHMENT
yAaxA mod p public key
yBaxB mod p public key
A
B
private key xA
private key xB
k yBxA mod p yAxB mod p axAxB mod p
system constants p prime number, a integer
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PERFECT FORWARD SECRECY

• Use a different DH key-pair on each exchange
• DH public keys need to be authenticated
• authentication can be done by many techniques
• Loss of long-term (authentication) keys does not
  disclose session keys

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PHASE 1 AUTHENTICATION ALTERNATIVES

• public-key signature
• preshared-key
• public-key encryption
• revised public-key encryption

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COOKIE EXCHANGE

• Phase 1 employs cookie exchange to thwart (not
  prevent) denial of service attacks
• A -gt B Cookie_Request
• As cookie, 64 bit random number
• B -gt A Cookie_Response
• includes A and Bs cookies
• all further Phase 1 and Phase 2 messages include
  both cookies
• ISAKMP SA is identified by both cookies
• IPSEC protocol SA is identified by SPI

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COOKIE GENERATION

• hash over
• IP Source and Destination Address
• UDP Source and Destination Ports
• a locally generated random secret
• timestamp

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IKE DEFAULT OAKLEY DH GROUPS

• Group 1
• MODP, 768 bit prime p, g2
• Group 2
• MODP, 1024 bit prime p, g2
• Group 3
• EC2N, 155 bit field size
• Group 4
• EC2N, 185 bit field size
• private groups can be used

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IKE NOTATION
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IKE NOTATION
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SKEYS, HASH AND SIG
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MAIN MODE WITHDIGITAL SIGNATURES
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AGGRESSIVE MODE WITHDIGITAL SIGNATURES
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MAIN AND AGGRESSIVE MODE WITH PRE-SHARED KEY
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MAIN MODE WITHPUBLIC KEY ENCRYPTION
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AGGRESSIVE MODE WITHPUBLIC KEY ENCRYPTION
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AUTHENTICATION WITH PUBLIC-KEY ENCRYPTION

• does not provide non-repudiation
• provides additional security since attacked must
  break both
• DH key exchange
• public-key encryption
• provides identity protection in aggressive mode
• revised protocol reduces public-key operations

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MAIN MODE WITH REVISED PUBLIC KEY ENCRYPTION
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MAIN MODE WITH REVISED PUBLIC KEY ENCRYPTION
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AGGRESSIVE MODE WITH REVISED PUBLIC KEY ENCRYPTION
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PHASE 2 QUICK MODE
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PHASE 2 QUICK MODE
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PHASE 2 QUICK MODE
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PHASE 2 QUICK MODE
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NEW GROUP MODE

• sandwiched between phase 1 and 2
• group can be negotiated in phase 1
• new group mode allows nature of group to be
  hidden
• in phase 1 only group id is communicated in clear

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NEW GROUP MODE