What is an MD5 hash?

The md5() function calculates the MD5 hash of a string. The md5() function uses the RSA Data Security, Inc. MD5 Message-Digest Algorithm.

From RFC 1321 – The MD5 Message-Digest Algorithm: “The MD5 message-digest algorithm takes as input a message of arbitrary length and produces as output a 128-bit “fingerprint” or “message digest” of the input. The MD5 algorithm is intended for digital signature applications, where a large file must be “compressed” in a secure manner before being encrypted with a private (secret) key under a public-key cryptosystem such as RSA.”

To calculate the MD5 hash of a file, use the md5_file() function.

Calculate the MD5 hash of the string “123456abcdef”:

<?php
$str = "123456abcdef";
echo md5($str);
?>