Rabins Fingerprinting

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Rabins Fingerprinting

• Presenter Tong Zhou

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Fingerprinting

• What is k-bit fingerprinting scheme?
• Function set
• where O is the set of all possible objects
• So that , With high
  probability, we have
• Note fingerprinting may have false alarms, i.e.,

while
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Rabins Fingerprinting

• Given string
• A k-bit Rabin fingerprint is computed as
  follows
• Let
• Choose irreducible polynomial P(t)
• Compute Rabins fingerprint f(A)

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Example of Rabins Fingerprinting

• Given bit string A101010, compute 4-bit Rabins
  fingerprint, choose p11111

1 0 1 0 1 0
1 1 1 1 1
1 0 1 0 1
1 1 1 1 1
1 0 1 0
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Properties of Rabins Fingerprinting

• For bit object string, the only operation needed
  is shift and xor
• Linear computation time
• Not secure this is NOT a one-way hash!

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Application Examples

• String matching can we find string y1y2ym in
  the string x1x2xn?

Straightforward Solution
x1 x2 x3 x4 x5 x6 x7 x8 xn
Time Complexity O(mn)
X
y1 y2 y3 y4 ym
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Application Examples

• String matching can we find string y1y2ym in
  the string x1x2xn?

Rabins Fingerprinting
f (y1 y2 y3 y4 ym)
Note Time complexity of computing f(x2x3xm1)
from f(x1x2xm) is O(1)
f(x1x2xm)
f(x2x3xm1)
Time complexity O(mn)
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Application Examples

• String matching can be used in
• Detecting worms 2 3
• Web cache 4
• Large file finding 5

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Application Examples

• Fingerprinting DAGs

Goal Give the vertices derived in the same way
from the same source the same tag. e.g., vertices
B C should have the same tag.
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Application Examples

• Fingerprinting DAGs
• Choose k-degree polynomial P(t) and random
  permutation T
• Tag(source) T(f(source) )
• For a vertex vi, assume it has n predecessors p1,
  , pn, Tag(vi)T(f(Tag(p1)Tag(pn)) )

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Application Examples

• Fingerprinting DAGs

0010
Example Choose S100000, P 11111 to generate a
4-bit fingerprint, T 3241
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Application Examples

• Fingerprinting DAG is used to
• Identify derived objects
• I guess it can also be used to fingerprint
  database structure

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References

• 1 A. Z. Broder. Some applications of Rabin's
  fingerprinting method. In Sequences II Methods
  in Communications, Security, and Computer
  Science, pages 143152. Springer-Verlag, 1993.
• 2 H. Kim and B. Karp, Autograph Toward
  Automated, Distributed Worm Signature Detection,
  Proceedings of the 13th Usenix Security
  Symposium, Aug. 2004.
• 3 S. Singh, C. Estan, G. Varghese and S.
  Savage, Automated Worm Fingerprinting, OSDI, 2004
• 4 L. Fan, P. Cao, J. Almeida and A. Broder,
  Summary Cache A Scalable Wide-Area Web Cache
  Sharing Protocol, IEEE/ACM Transactions on
  Networking, vol. 8, No. 3, 2000
• 5 U. Manber, Finding Similar Files in a Large
  File System. Proceedings of the USENIX Winter
  Technical Conf., 1994.