Hash Function Uniqueness and Collision

hash-uniqueness.sh

#!/bin/bash

# Calculates hash uniqueness.
# 
# Usage:
#
#     hash-uniqueness.sh PROGRAM LENGTH WINDOW
#
#     hash-uniqueness.sh md5sum
# 
#     hash-uniqueness.sh crc32sum 8 4
# 
#     hash-uniqueness.sh sha256sum 32 6
#

program=$1
length=${2:-32}
window=${3:-8}

# mimic md5sum
function crc32sum {
	cksum "$1" | awk '{ $1=sprintf("%08x", $1); print $1, $3 }';
}

mkdir -p /run/shm/words;

for i in $(cat /usr/share/dict/american-english /usr/share/dict/british-english /usr/share/dict/brazilian /usr/share/dict/portuguese | sort | uniq); do [ ! -f "/run/shm/words/$i" ] && echo "$i" > "/run/shm/words/$i"; done;

[ -f /run/shm/words.$program ] && [ -d /run/shm/words ] && [ "$(cat /run/shm/words.$program | wc -l)" -ne "$(find /run/shm/words -type f | wc -l)" ] && rm -f /run/shm/words.$program;
[ ! -f /run/shm/words.$program ] && for i in $(find /run/shm/words -type f | sort | uniq); do $program "$i" >> /run/shm/words.$program; done;

counter=0
accumulator=0
maximum=$(find /run/shm/words -type f | wc -l)

for i in $(seq 1 $(( $length - $window )) ); do
	counter=$(( counter + 1 ))
	accumulator=$(( $accumulator + $(cut -c $i-$(( $i + $window - 1 )) /run/shm/words.$program | sort | uniq | wc -l) ))
done;

echo "uniqueness: $( echo "( 100.0 * ( $accumulator / $counter ) ) / $maximum " | bc -l ) %";
echo "collisions: $( echo "100.0 - ( 100.0 * ( $accumulator / $counter ) ) / $maximum " | bc -l ) %";

More Examples

Dictionaries in /usr/share/dict/: american-english british-english brazilian portuguese (~500k words)

Length = 8, Window = 6

time ./hash-uniqueness.sh crc32sum 8 6;
uniqueness: 98.28423716106460077470 %
collisions:  1.71576283893539922530 %

real	42m5,849s
user	3m24,297s
sys	61m30,946s

Length = 32, Window = 8

time ./hash-uniqueness.sh md5sum 32 8;
uniqueness: 99.99289907488395555370 %
collisions:  0.00710092511604444630 %

real	43m16,163s
user	2m4,602s
sys	41m37,513s

time ./hash-uniqueness.sh sha1sum 32 8;
uniqueness: 99.99362218334791119996 %
collisions:  0.00637781665208880004 %

real	43m2,839s
user	2m5,084s
sys	41m22,939s

time ./hash-uniqueness.sh sha256sum 32 8;
uniqueness: 99.99338355755480583670 %
collisions:  0.00661644244519416330 %

real	42m39,301s
user	2m8,414s
sys	40m56,361s

time ./hash-uniqueness.sh xxh128sum 32 8;
uniqueness: 99.99361495226327164350 %                                 
collisions:  0.00638504773672835650 %

real	33m40,216s
user	1m13,208s
sys	32m54,345s