Package org.xlattice.crypto.filters

Class KeySelector

java.lang.Object
org.xlattice.crypto.filters.KeySelector
public class KeySelector
extends Object
Given a key, populates arrays determining word and bit offsets into a Bloom filter.
Author:
Jim Dixon BloomSHA1.java and KeySelector.java are BSD licensed from the xlattice app - http://xlattice.sourceforge.net/ minor tweaks by jrandom, exposing unsynchronized access and allowing larger M and K. changes released into the public domain. As of 0.8.11, bitoffset and wordoffset out parameters moved from fields to selector arguments, to allow concurrency. ALl methods are now thread-safe.

  • Constructor Details

    • KeySelector

      public KeySelector​(int m, int k)
      Creates a key selector for a Bloom filter. When a key is presented to the getOffsets() method, the k 'hash function' values are extracted and used to populate bitOffset and wordOffset arrays which specify the k flags to be set or examined in the filter.
      Parameters:
      m - size of the filter as a power of 2
      k - number of 'hash functions' Note that if k and m are too big, the GenericWordSelector blows up - The max for 32-byte keys is m=23 and k=11. The precise restriction appears to be: ((5k + (k-1)(m-5)) / 8) + 2 < keySizeInBytes It isn't clear how to fix this.

  • Method Details

    • getOffsets

      public void getOffsets​(byte[] key, int[] bitOffset, int[] wordOffset)
      Given a key, populate the word and bit offset arrays, each of which has k elements.
      Parameters:
      key - cryptographic key used in populating the arrays
      bitOffset - Out parameter of length k
      wordOffset - Out parameter of length k
      Since:
      0.8.11 out parameters added

    • getOffsets

      public void getOffsets​(byte[] key, int off, int len, int[] bitOffset, int[] wordOffset)
      Given a key, populate the word and bit offset arrays, each of which has k elements.
      Parameters:
      key - cryptographic key used in populating the arrays
      bitOffset - Out parameter of length k
      wordOffset - Out parameter of length k
      Since:
      0.8.11 out parameters added