Stein65 Slide 1

1
PWsecuritymeasures

• PWE3 65th IETF
• 21 March 2005

Yaakov (J) Stein
2
Reminder

• At IETF64 security threats were presented
• PWs have special features that may be exploited
  by hackers
• PW control plane does not mandate authentication
• PW user packets have no authentication/encryption
  options
• draft-stein-pwe3-sec-req-00.txt reviews security
  requirements
• here we will mention a few solution ideas

3
Control Protocol Authentication

• Problem
• many of the attacks in draft-stein-pwe3-sec-req-00
  .txt can be avoided
• if it is not possible to impersonate a PE
• thus PWE control protocol needs a strong
  authentication mechanism
• Solution 1 MD5
• use MD5 signature option (shared key per peer)
  per RFC3036
• TCP segments of every LDP message (even hellos)
  are authenticated
• MD5 may be replaced by SHA-1 or any other message
  digest
• Solution 2 authentication TLV for
  initialization
• new optional TLV in the initialization message
• use public key mechanism
• reject if no authentication TLV or if
  authentication fails

4
PW Packet Authentication

• Problems
• PW label is the only identifier in packet
• CW sequence number can be used for DoS attack
• Solution
• add optional authentication field between control
  word and payload
• (becomes a control word extension)
• lightweight option
• 32 bit CW extension (must be negotiated via a new
  LDP TLV)
• computed based on limited-size input, for
  example
• sequence number salt
• sequence number checksum of payload
• heavyweight option
• 64 or 128 bit CW extension (must be negotiated
  via a new LDP TLV)
• hash of sequence number payload
• WARNING if performed in SW enables DoS attack

5
PW Packet Encryption

• at IETF-64 we discussed encrypting the PW payload
• Problem
• PW is not reliable may lose packets (dont even
  know how many bytes lost)
• so, cant use stream cipher, CBC, CFB, etc. modes
• Solution 1
• use ECB mode on sequence number payload
• (including sequence number blocks replay attacks)
• Solution 2
• generate per-packet key based on secret key and
  sequence number
• use ECB mode on payload