break the nsa encryption

nsa.php

<?php
/**
* Encrypts a given plaintext using the supplied key.
*
* @param  key  		a numeric key with a value greater than 255
* @param  plainText  	a string containing the plaintext you want to encrypt
*
* @return number   	a unique number for this given key and plaintext
*/
function nsaEncrypt($key, $plainText)
{ 
	$result = 0;

	for ($character = 0; $character < strlen($plainText); $character++)
	{
		$result = bcadd($result, ord($plainText[$character]));
		$result = bcmul($result, $key);
	}

	return $result;
}


/*

Here’s the ciphertext you need to deal with. It represents the encrypted version of a md5 hash. Decrypt it and then crack the hash to get the solution.

434384569820012709749978085023147407174684824178941182826833799495931410023794845922767533429746537016995520506439457550763575993604402054742042654701475990703513534158579743446096171193503041071008550601683001839024513922875537448251544812606790879783442587227277601837740236112564627038091170167413493638174350319534049389495771259593223970367601200671312435588244337256711215093040169407379877379400242759675821842258110296156050808143302683071999772732555638568114446076107646435540182476596386155629693774180289540430199704239923354089531930534807431109632462125230336414045829798557815327441670222304200

*/