Efficient Time-Bound Hierarchical Key Assignment Scheme

1
Efficient Time-Bound Hierarchical Key Assignment
Scheme

• Source IEEE Transactions on Knowledge
• and Data Engineering, Vol. 16,
• No. 10, Oct. 2004, pp. 1301-1304
• Authors Hung-Yu Chien
• Speaker Chia-Lin Kao
• Date 2004/09/22

2
Outline

• Introduction
• Proposed scheme
• Conclusions

3
Introduction
A
C
B
F
D
E
4
Notations

• Role Ci, Cj, TA(Trusted Agent)
• Data in Cards IDi, ki, ht1(a), hz-t2(b), X
• ki secret key for Ci
• a, b random secret values at TA
• z max time periods
• hm(x) h(h((h(x))))
• Ki,t key for Ci at time t
• h() a secure one-way hash function

5
Proposed Scheme

• Initialization
• TA randomly selects n secret key ki, 1in, and
  two random secret values a and b.
• TA publishes a public value rij on an
  authenticated public board.
• X is TAs secret key

rijh(XIDiIDjki) ?kj
6
Proposed Scheme

• User Registration
• TA distributes ki to Ci through a secure channel.
• TA also issues the user a tamper-rsistant device
  in which TAs secret key X, and the identity of
  Ci, IDi, ht1(a), hz-t2(b) are stored.

7
Proposed Scheme

• Encrypting Key Gneration
• At time t (t1tt2), the data belonging to Cj
  would be encrypted by the key Kj,t
• Kj,th(kj?ht(a)?hz-t (b))

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Proposed Scheme

• Decrypting Key Derivation
• Ci inputs rij, IDj, and ki
• deivce computes kj by kjrij?h(XIDiIDjki)
• ht(a)ht-t1(ht1(a))
• hz-t(b)ht2-t(hz-t2(b))
• Kj,th(kj?ht(a)?hz-t (b))

rijh(XIDiIDjki) ?kj
t1tt2
9
Conclusions

• New time-bound key assignment scheme based on a
  low-cost tamper-resistant device.
• Without public key cryptography, our scheme
  greatlyreduces the computational load and the
  implementation cost.