Decrypt MD5 hash to String with PHP

Question

How can I decrypt an MD5 hash to a string using PHP?

Hash functions are one way functions: http://en.wikipedia.org/wiki/Hash_functions — Felix Kling, Mar 21 '11 at 23:37
www.freerainbowtables.com tries to reverse engineer simple passwords, but the idea is that MD5 should remain a mystery. — Patrick Beardmore, Mar 21 '11 at 23:58

score 4 · Answer 1 · answered Mar 21 '11 at 23:36

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Hashing isn't encryption - you can't.

answered Mar 21 '11 at 23:36

Erik

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you can with collisions. – RobertPitt Mar 21 '11 at 23:58
In some how he can crack it by generating hash's and compare it against what he want like world list. – SIFE Mar 22 '11 at 00:02
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No he can't. He can potentially find data that produces the same hash. He cannot reliably regenerate the original string. – Erik Mar 22 '11 at 00:11

score 3 · Answer 2 · answered Mar 21 '11 at 23:52

There is no way to decrypt a hash. Hash functions are, by nature, 1 way functions.

if you're trying to create encryption for users data then you should be using normal encrypt/decrypt functions.

If you're trying to decrypt 'hashed' passwords, well.... good luck with that one.

score 2 · Answer 3 · edited May 23 '17 at 09:58

You should read up on what it actually does before you assume its decryptable, im not going to go into much detail but MD5 is infact floored and should not be used at all.

MD5 hashes can collide meaning to totally different strings can produce the same hash, causing a exploit in the algorithm.

if you want a 2 way encryption you should do something like so:

$key = 'password to (en/de)crypt';
$string = 'string to be encrypted';

//Encrypt
base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256,md5($key),$string,MCRYPT_MODE_CBC,md5(md5($key))));

//Decrypt
rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($string), MCRYPT_MODE_CBC, md5(md5($key))), "\0");

As quoted from: Best way to use PHP to encrypt and decrypt passwords?

score 0 · Answer 4 · answered Mar 21 '11 at 23:58

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If you're looking for decryption, you can create (or get) rainbow tables - essentially, create a password generator that encrypts with MD5 and invent as many hashes as you want. Save the hashes to a database. From there, do a search for your hash.

answered Mar 21 '11 at 23:58

thebarless

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Decrypt MD5 hash to String with PHP

4 Answers4