Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) ‏

1. Robert Moskowitz (ICSAlabs/VzB) Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)‏ Submission Title: Key Negotiation using DIET HIP Date Submitted: 28 June, 2010 Source: Robert Moskowitz (ICSA labs, an Independent Division of Verizon Business)‏ Address: Detroit, MI USA Voice:[…], FAX: […], E-Mail: robert dot moskowitz at icsalabs dot com Re: A very light key negotiation protocol using standard components Abstract: Even with recent enhancements, the Host Identity Protocol base EXchange, RFC 5201-bis is still considered too much for sensor. This document presents the HIP DIET Exchange; a truly minimalistic key exchange protocol.. Purpose: Present the HIP key negotiation protocol, what changes are necessary to lighten it, and then the design of the DIET Exchange. Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

2. Robert Moskowitz (ICSA labs, an Independent Division of Verizon Business)‏ Key Negotiation using DIET HIP Robert Moskowitz (ICSAlabs/VzB)

3. Robert Moskowitz (ICSAlabs/VzB) Purpose of this presentation • Present work on a new HIP Exchange specifically architected for resource limited devices by • Explaining what HIP is and does • Review cryptographic components used in HIP (and many other Key Management Systems (KMS) • Work through what might be a minimal cryptographic for a KMS • Explain the new HIP Diet Exchange (HIP DEX)

4. What is HIP? • RFC 4423 introduces the Host Identity Namespace. When the Host Identity (HI) is a Cryptographic key (RSA, DSA, or ECC) • 128 bit Host Identity Tag (HIT) is derived from the HI (hashed) and functions as an IPv6 address (/28 prefix) for applications

5. What is HIP? • A 4 packet Peer-to-Peer Host Identity Protocol Base EXchange (HIP BEX) establishes a security association (SA, similar to IKE), indexed by the HITs, but independent of the IP address • HIP's notion of an End Point Identifier (the HITs) disassociates the current tight binding between the Internetwork and Transport layers • Can even function directly on layer 2

6. What is HIP? • The SA is used to key ESP (RFC 4304) in transport mode • Or could key IEEE 802.15.4 MAC security

7. More on HIP • Host Identity validation is not built into HIP. It can be handled • Anonymously – you get what you pay for • Man-in-the-middle attacks if both peers are anonymous • No MITM attack if one peer can validate HIT of the other • ACLs – management up to implementation • DNS – RFC 5205 • No reverse lookup, but FQDN in BEX • X.509 certificates – Internet Draft draft-ietf-hip-cert-03.txt

8. Robert Moskowitz (ICSAlabs/VzB) What is the role of HITs? • In HIP the End Point Identifier is • Host Identity Tag (HIT) in IPv6 • Local Scope Identifier (LSI) in IPv4 • HITs and LSIs are typically only known to the applications and do not transit the network • Applications tend to be ignorant of underlying IP addresses, if any • Secure mobility WORKs (RFC 5206) • IPv4 applications on IPv6 networks

9. Robert Moskowitz (ICSAlabs/VzB) More on HIP • HIP is architecturally ideally suited to be a Key Management System (KMS) for both IP and MAC layers • Current status • RFC 4423, 5201-5206 • Three implementations • Boeing, Ericsson, HIPL • Going through revisions, -bis Internet Drafts available

10. Robert Moskowitz (ICSAlabs/VzB) HIP BEX is SIGMA Compliant • Authenticate Diffie-Hellman key exchange with SIGning and MACing • Also used by IKEv2 • Defined by Hugo Krawczyk • Technion University and IBM • Origin and theory: • http://webee.technion.ac.il/~hugo/sigma.ps • Diffie-Hellman based • 3 packets typical • Ephemeral Diffie-Hellman provides Perfect Forward Secrecy (PFS) • Use of MAC proves correctness of the DH key and thereby guarantees freshness

11. The Basics of the HIP exchange • DH list ::= List of Diffie-Hellman formats supported • Puzzle ::= computational challenge to limit flooding attacks • Solution ::= solution to puzzle • HI ::= Host Identity Public key • Sig ::= Digital Signature using Host Identity • Mac ::= Message Authentication using Diffie-Hellman derived key

12. Robert Moskowitz (ICSAlabs/VzB) The Basics of the HIP exchange • 4 packet exchange to deal with flooding attacks Initiator Responder I1: DH list --------------------------> select precomputed R1 <------------------------- R1: puzzle, D-H list, HI, sig check sig remain stateless solve puzzle I2: solution, D-H, {HI}, mac, sig --------------------------> compute D-H key check puzzle check mac & sig <-------------------------- R2: mac, sig check mac & sig compute D-H

13. Robert Moskowitz (ICSAlabs/VzB) HIP Cryptographic Components • 'Public' Key • RSA, DSA, or ECDSA • Hashing • SHA-1, SHA-256, SHA-384 • HMAC • Diffie-Hellman • Modulo and Elliptic Curve • AES • Many modes of operation supported through ESP from IPsec

14. Robert Moskowitz (ICSAlabs/VzB) A minimal HIP implementation • Least amount of Crypto • ECDSA, SHA-1, HMAC, ECDH, AES-CCM • Still a lot of crypto and code • ECDSA keys derived at device setup • ECDH keys 'ephemeral' but lifetime could be extended to when symmetric keys are exhausted (once a month?) • Code space more concern if long-term keys are used • Can we do with less?

15. Robert Moskowitz (ICSAlabs/VzB) General KMS 'review' • Step back and review the components of a Key Management System • Exclude Password based approaches from consideration • Password installation IS the KMS, that is a manual KMS • 'Public' key based approaches only proven method • Must prove ownership of the private key while providing a shared secret key • TLS uses Key encryption by the public key • IPsec uses ephemeral Diffie-Hellman key exchange

16. Robert Moskowitz (ICSAlabs/VzB) Crypto 'review' • Diffie-Hellman based secrets are NOT uniformly distributed (this IS important!) • From draft-irtf-cfrg-kdf-uses-00.txt • Must be passed through a Key Derivation Function to 'Extract' a uniformly random key (e.g. HMAC) • But if only used to encrypt a uniformly random session key, this is mitigated

17. Robert Moskowitz (ICSAlabs/VzB) Crypto 'review' • If Hashing is removed • HMAC is removed • CMAC is be a partial replacement • Puzzle construction and Key Expansion • Diffie-Hellman is limited • Common practice is to use with HMAC • But can encrypt a session key • Public Key Signatures are lost • Requires Hashing to avoid forgeries • CMAC cannot protect against forgeries

18. Robert Moskowitz (ICSAlabs/VzB) Putting HIP on a DietBasic premise • Use static ECDH as Host Identities • With ECDH derived key only used for session key protection • Randomly generated a key and encrypted with DH derived key for transmission • This replaces the Diffie-Hellman key as the session key which required HMAC • Key derivation from random key can use CMAC • We do not need a hash function! • We can 'manage' without Digital Signatures

19. Putting HIP on a DietProof of Identity • Nonce encrypted with session key 1st proof • Session key used in MAC of HIP payload 2nd proof • Thus sender of packet must have private key matching HI • The WHO of the HI is outside of HIP • Various methods used • ACL, DNS, X.509 • Anonymous with password authentication

20. Putting HIP on a DietWhat security assertions lost? • Use of static DH means loss of Perfect Forward Secrecy (PFS) • Static DH (NIST SP 800-56A sec 6.3.2) used as device identities • If Private key is compromised, all prior secrets encrypted with it are compromised • PFS CAN be approached as each party contributes to the initial key in a hidden manner

21. Robert Moskowitz (ICSAlabs/VzB) Putting HIP on a DietWhat security assertions lost? • Digital signatures • ECDSA requires a hash • Collision resistance required to avoid existential forgeries. • This sacrifice means deviating from SIGMA • But could follow closely

22. Robert Moskowitz (ICSAlabs/VzB) Putting HIP on a DietOther uses of hashing in HIP BEX • Use CMAC in puzzle creation and solution • Find a 'simple' compress function for HIT creation • 160, 224, or 256 bits down to 96 with collision avoidance. • Possibly Matyas–Meyer–Oseas hash? • Since ECDH public key is exponentiation with a random secret, right truncation can be used for HIT construction.

23. Robert Moskowitz (ICSAlabs/VzB) Putting HIP on a DietSummary of Crypto Components • A 'Dietetic' HIP exchange CAN be achieved with • AES-CCM (and CMAC) • Static ECDH • Proves private key ownership • Following is DEX protocol • The network is the attacker model used • Assume both malicious Responder and Initiator

24. Robert Moskowitz (ICSAlabs/VzB) HIP Diet Exchange (DEX) • Parties are • I ::= Initiator • R ::= Responder • MR ::= Malicious Responder • MI ::= Malicious Initiator • Functions are • ECR ::= AES encrypt • MAC ::= CMAC • | ::= concatenation • EX ::= Key expansion extraction

25. Robert Moskowitz (ICSAlabs/VzB) HIP Diet Exchange (DEX) • Values are • PK ::= Public key of • e.g. Pki is Public key of I • DH ::= Derived Diffie-Hellman key • n ::= nonce • Pn ::= Puzzle based on and containing nonce n • Sn ::= Puzzle solution based on nonce n • x,y ::= random secrets

26. Robert Moskowitz (ICSAlabs/VzB) HIP Diet Exchange (DEX) • The HIP DEX exchange is identified by a DEX HIT I or MI R or MR I1 ::= () ------> R1 ::= <--- Pn, PKr I2 ::= Pn, Sn, PKi, ECR(DH,x|n), MAC(x,(Pn, Sn, PKi, ECR(DH,x|n))) ------> I or MI R R2 ::= <--- ECR(DH,y|n), MAC(x, (ECR(DH,y|n))) I R <--- Data, MAC(EX(x,y), Data) ------> Note be end of exchange, parties can ONLY be R and I.

27. Robert Moskowitz (ICSAlabs/VzB) HIP Diet Exchange (DEX)Dealing with a lossful network • HIP BEX can be slow with packet loss • DEX MUST deal with high packet loss • Implement a repeated send until ACK • I aggressively sends I1 and continues send it until it receives R1 • R sends R1 for every I1 received • I aggressively sends I2 and continues send it until it receives R2, then it transitions to connected state • R sends R2 for every I2 received, it transitions to connected state when it starts receiving datagrams

28. Robert Moskowitz (ICSAlabs/VzB) HIP Diet Exchange (DEX)Dealing with a lossful network • Plus error handling events. • E.G. I ignores R1s unless it has has sent an I1 • This does have a battery drain attack • M sends an I1 to R that looks as if it came from sensor Q • On analysis really not different from any other reflector battery attack

29. Robert Moskowitz (ICSAlabs/VzB) HIP Diet Exchange (DEX)Adding Password Authentication • Password Augmented Authentication • Provides bootstrap mechanism to add a client to a server • Supports emergency adHoc access • EMT access to a Pacemaker • Utility field technician to a substation controller • Server implicitly invites password Auth • R1 ALWAYS contains a challenge • Initiator encrypts challenge with password and encrypts that in Responder's Public key

30. Robert Moskowitz (ICSAlabs/VzB) HIP Diet Exchange (DEX)Adding Password Authentication • Challenge Encryption • Use password as CMAC key • MAC nonce from R1 puzzle • RFC 4615 (AES-CMAC-PRF-128) is starting point • Encrypting a challenge from R1 prevents replay attacks • R1 cannot be reused if password response is accepted • 'Rogue' Responder attack • I cannot tell if R1 came from Responder or attacker unless PKr from another source • Need zero knowledge alternative • As in IEEE 802.11s

31. Robert Moskowitz (ICSAlabs/VzB) Using HIP DEX for MACsec • HIP runs directly over MAC • Use 802.1X ethertype? • How to handle fragmentation • ICMP error messages • Remove IP header and run directly over MAC • No other considerations

32. Robert Moskowitz (ICSAlabs/VzB) Conclusions • HIP DEX significantly reduced requirements over HIP BEX • Uses established cryptographic functions • Easily analysed • Full state machine for all event conditions • KMS for both IP and MAC layers • Further coding advantage • Performs over lossful networks

33. Robert Moskowitz (ICSAlabs/VzB) Developing HIP DEX • Publish HIP DEX Internet Draft • By July 5 2010 • Present at IETF in Maastricht • Work with potential implementers/testers

34. Robert Moskowitz (ICSAlabs/VzB) Questions?