A simple Q. about MD5

[Anon]

Hi,
Is it possible to "unMD5" a srting?
for example:
$password=md5('123') // $password will be "202cb962ac59075b964b07152d234b70"
So,is it possible to know $password is "123" by "unMD5" the string "202cb962ac59075b964b07152d234b70"??
Sorry for my english!

[rrijnders]

No. MD5 is a "one way" hash. It is designed that way.

-- Rich

[Anon]

Think about it:

1) There are an infinite number of possible messages that can be MD5'd.

2) There are exactly 2¹²⁸ possible MD5 hashes - which is a lot less than any infinite number.

So there is at least one MD5 string which is the hash of an infinite number of messages - so which message is it supposed to "unMD5" to? (And of course, the likelihood is that all MD5 strings have this property.)