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Cryptography for Backup Navigation

Cryptography for Backup Navigation. Dan Boneh Stanford University. Introduction. Focus of this talk: Data integrity (not confidentiality) An overview of identity-based cryptography Applications to ADS-B and DME. Verify tag: F (k , m) = `tag’. ?. Data integrity 1: MAC .

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Cryptography for Backup Navigation

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  1. Cryptography for Backup Navigation Dan Boneh Stanford University

  2. Introduction • Focus of this talk: • Data integrity (not confidentiality) • An overview of identity-based cryptography • Applications to ADS-B and DME

  3. Verify tag: F(k, m) = `tag’ ? Data integrity 1: MAC • Difficulty with MACs: key management • both sides must have the same secret key k k Message m tag Generate tag: tag  F(k, m)

  4. Example MAC: (E) CBC-MAC m[0] m[1] m[3] m[4]     E(k,) E(k,) E(k,) E(k,) E(k1,) key := (k, k1) message := (m[0], …, m[L]) tag

  5. Problem: broadcast Integrity The problem: Sta3 can forge messages to all others (note: TESLA) k Sta1 k msg tag k Sta2 k Sta3

  6. Data integrity 2: Dig. Signatures PK Bob1 SK msg sig PK Bob2 sig S( SK, m) SK: secret key PK: public key PK Bob3 • Ensures broadcast integrity • Difficulty: (1) message needs to include PK and certificate • [ msg, sig, PK, cert ] • (2) revocation ? V( PK, m, sig) = `yes’ (100s of bytes)

  7. Modern Signatures [BLS’01] • Pairings <X,Y>: ,: <X, Y> = <X, Y> • Signatures: fix an element g • Secret Key:  Public Key: g • Sign( SK, M): sig = H(M)(20 bytes) • Verify( PK=g, M, sig=H(M) ): test if <g , sig> = <PK, H(M)> <g, H(M)> <g , H(M)>

  8. Performance • MACs: built from fast block ciphers • Time for short messages (<1KB): 1s • Length: 32 to 128 bits • Signatures: built from algebraic functions • sign/verify time for short messages: 10ms • Length: 20 bytes [BLS’01]

  9. identity-based crypto

  10. Identity-based Crypto • The basic idea [Shamir 1984] • A cryptosystem where anything is a public key • Examples: 24-bit plane ID , pilot name , current date • Practical systems: [BF 2001, …] • Based on new tools: pairings on elliptic curves • Commercially deployed (e.g. Voltage Security) master-key my ID is “652A4B” here is your secret key: SK PKG

  11. ex 1: identity-based key exchange • SKID1 and SKID2 generated at manufacturing time • Updated periodically during maintenance • Automatic revocation: ID = (plane-ID , month, year) my ID is ID1 SKID1 SKID2 my ID is ID2 shared key = F(ID1, SKID2) shared key = F(ID2, SKID1)

  12. Application to DME or ADS-B (MLAT) • Ping-pong protocol K1 ID1 SK1 ID1, data, MAC ID K2 ID2, data, MAC ID2 SK2 ID SKID ID3, data, MAC ID3 SK3 K1, K2, K3 verify MACs K3  Symmetric MACs with minimal overhead

  13. Repeated authentication • Initial setup requires computing a MAC key • time  20ms • Subsequent messages can be authenticated using established key:  1s / msg

  14. identity-based signatures: ADS-B [ID, data, sig] ID SKID master-key verify sigusing ID no need for plane to transmit PK or certificate PKG

  15. Performance • ID-based crypto: built from pairings on elliptic curves • Time: dominated by pairing computation software: 20ms (1GhZ x86) hardware: 90s (FPGA) • ID-based signature length: 40 bytes • open problem: 20-byte ID-based sigs

  16. THE END

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