org.passay.dictionary

Class BloomFilterDictionary

java.lang.Object

org.passay.dictionary.BloomFilterDictionary

All Implemented Interfaces:

Dictionary

public class BloomFilterDictionary
extends Object
implements Dictionary

Dictionary that is backed by a Bloom Filter. WARNING bloom filters may return true for a word that is NOT in the dictionary. This implementation should only be used if false positives can be tolerated.

Author:

Middleware Services

Constructor Summary

Constructors

Constructor and Description
BloomFilterDictionary(com.google.common.hash.BloomFilter<String> bf) Creates a new dictionary instance from the supplied BloomFilter.

Method Summary

Modifier and Type	Method and Description
com.google.common.hash.BloomFilter<String>	getBloomFilter() Returns the bloom filter used for searching.
boolean	search(String word) WARNING bloom filters may return true for a word that is NOT in the dictionary.
long	size() Returns an estimate for the number of words added to the dictionary.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

BloomFilterDictionary

public BloomFilterDictionary(com.google.common.hash.BloomFilter<String> bf)

Creates a new dictionary instance from the supplied BloomFilter. The fpp (false-positive probability) parameter of the given Bloom filter is a vitally important configuration concern. If it is too high, one risks user frustration due to rejection of valid passwords; if it is too low, one risks excessive storage costs. Finding the proper balance between acceptable user experience and storage costs is worth the time and effort required in testing. The Guava default value of 3% is likely unsuitable for many if not most deployments.

Parameters:

bf - bloom filter used to determine if a word exists.

Method Detail

getBloomFilter

public com.google.common.hash.BloomFilter<String> getBloomFilter()

Returns the bloom filter used for searching.

Returns:

bloom filter

size

public long size()

Returns an estimate for the number of words added to the dictionary. See BloomFilter.approximateElementCount().

Specified by:

size in interface Dictionary

Returns:

approximate number of words in the dictionary

search

public boolean search(String word)

WARNING bloom filters may return true for a word that is NOT in the dictionary. Please make sure you understand how bloom filters work before using this implementation. @see Bloom Filter and BloomFilter.mightContain(Object).

Specified by:

search in interface Dictionary

Parameters:

word - to search for

Returns:

true if the word might be in the bloom filter, false if the word is definitely not in the bloom filter

toString

public String toString()

Overrides:

toString in class Object