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.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	KeySelector.BitSelector
class	KeySelector.GenericBitSelector	Extracts the k bit offsets from a key, suitable for general values of m and k.
class	KeySelector.GenericWordSelector	Extracts the k word offsets from a key.
static interface	KeySelector.WordSelector

Constructor Summary

Constructors

Constructor	Description
KeySelector(int m, int k)	Creates a key selector for a Bloom filter.

Method Summary

Modifier and Type	Method	Description
void	getOffsets(byte[] key, int[] bitOffset, int[] wordOffset)	Given a key, populate the word and bit offset arrays, each of which has k elements.
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.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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