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• We know where we’re going on what to do once CAs have keys.
• Getting CA keys from pairwise keys is straightforward.
• Little work on initial keying for CA keys
• Channel for data– Meant for tunneling EAP, etc.
• Need simple, out of the box way to install keys
Progress in AF
Use Case
• New device, need to set it up with pairwise key(s)
• Neighbors should be able to agree on pairwise keys with little manual intervention
• Would like a way to identify “my” devices and validate them.
Proposal (1)
• Assign devices unique 128-bit IDs– Loaded with MAC address– 32 bits is a vendor identifier– 96 bits is vendor dependent, but must be unique
• Random number is perfectly fine– The idea: give IDs to devices as a simple ACL
Proposal (2)
• Use RSA to validate device owns ID and exchange pairwise keys– Vendor generates and installs private key and
certificate w/ public key– Certificate is signed by a vendor’s signing
credentials– Vendor’s credentials are signed by a root
certification authority (CA)– IETF likely willing be that CA– CA would endorse vendor’s right to first 32 bits.– Vendor would endorse the validity of the
remaining bits.
• Net effect: unforgable credentials that facilitate enrollment
Simple Public Key Infrastructure
n ...
RootCA
FirstVendor
CA
SecondVendor
CA
3 2DeviceCert 1
n ... 3 2DeviceCert 1
Analysis
• Why not use MAC address?– MAC address forging is important to layer 2.– Devices may have many MAC addresses.
• Auxiliary benefits– Solves the layer 2 part of the ARP problem– Prevents counterfeiting hardware– Provides a basis for establishing trust in
firmware• Drawbacks
– Have to integrate with manufacturing process• Not costly• DOCSIS is doing something similar with cable modems
– Requires hash function for signing• Probably SHA1
Example establishment protocol
• SignCrypt encrypts arg1, auths both args
• Unique ID is encoded into certificate
1. A-> A_cert, SignCrypt(Ra, 0) -> B2. A<- B_cert, SignCrypt(Rb,Ra) <- B3. A-> AID, SignCrypt(0, Rb) -> B
• Shared secret is Ra XOR Rb• All signatures and certs validated • IDs checked to ACL• On race, M1 from lower unique ID wins
Summary
• Unique IDs on each device• Simple key management• Does not eliminate other
management methods– Credentials could be leveraged in centralized
management• Auxiliary benefits• Vendor must install keypair
