Introduction

The MD4, MD5 and SHA-1 algorithms are secure hash functions. They take a string input, and produce a fixed size number – 128 bits for MD4 and MD5; 160 bits for SHA-1. This number is a hash of the input – a small change in the input results in a substantial change in the output. The functions are thought to be secure, in the sense that it would require an enormous amount of computing power to find a string which hashes to a chosen value. In others words, there’s no way to decrypt a secure hash. The uses of secure hashes include digital signatures and challenge hash authentication.
This document is a good introduction to hashes

Create Secure Password

Using

hashParameter = loginID + webURL + mySecret

So only one password (mySecret) is needed to generate a personalized password for each website

loginID
webURL
mySecret
Calculate


Result (hex)
#This code is equivalent to the following Linux shell command
echo -n "myLogin@yahoo.commywebsite.comhello123" | sha1sum

#/bin/sh
loginID=myLogin@yahoo.com
webURL=mywebsite.com
secretKey=hello123
s=${loginID}${webURL}${secretKey}
echo $s
echo -n $s | sha1sum