md5

(PHP 4, PHP 5, PHP 7)

md5Calculate the md5 hash of a string

Warning

It is not recommended to use this function to secure passwords, due to the fast nature of this hashing algorithm. See the Password Hashing FAQ for details and best practices.

Description

md5 ( string $str [, bool $raw_output = FALSE ] ) : string

Calculates the MD5 hash of str using the » RSA Data Security, Inc. MD5 Message-Digest Algorithm, and returns that hash.

Parameters

str

The string.

raw_output

If the optional raw_output is set to TRUE, then the md5 digest is instead returned in raw binary format with a length of 16.

Return Values

Returns the hash as a 32-character hexadecimal number.

Examples

Example #1 A md5() example

<?php
$str 
'apple';

if (
md5($str) === '1f3870be274f6c49b3e31a0c6728957f') {
    echo 
"Would you like a green or red apple?";
}
?>

See Also

  • md5_file() - Calculates the md5 hash of a given file
  • sha1_file() - Calculate the sha1 hash of a file
  • crc32() - Calculates the crc32 polynomial of a string
  • sha1() - Calculate the sha1 hash of a string
  • hash() - Generate a hash value (message digest)
  • crypt() - One-way string hashing
  • password_hash() - Creates a password hash

add a note add a note

User Contributed Notes 8 notes

up
11
Ray.Paseur sometimes uses Gmail
5 months ago
md5('240610708') == md5('QNKCDZO')

This comparison is true because both md5() hashes start '0e' so PHP type juggling understands these strings to be scientific notation.  By definition, zero raised to any power is zero.
up
8
radon8472 at radon-software dot net
3 years ago
<?php
   
function raw2hex($rawBinaryChars)
    {
      return =
array_pop(unpack('H*', $rawBinaryChars));
    }
?>

The complement of hey2raw.
You can use to convert from raw md5-format to human-readable format.

This can be usefull to check "Content-Md5" HTTP-Header.

<?php
  $rawMd5   
= base64_decode($_SERVER['HTTP_CONTENT_MD5']);
 
$post_data = file_get_contents("php://input");

  if(
raw2hex($rawMd5) == md5($post_data)) // Post-Data is okay
 
else                                    // Post-Data is currupted
?>
up
0
Ken Guest
8 days ago
Use the strict comparision/identity operator:

php > var_dump(md5('240610708') == md5('QNKCDZO'));
php shell code:1:
bool(true)
php > var_dump(md5('240610708') === md5('QNKCDZO'));
php shell code:1:
bool(false)
php >

because, as mentioned previously, using the equality operator may result in false positives.
up
-2
hkmaly
1 year ago
Note: Before you get some idea like using md5 with password as way to prevent others tampering with message, read pages "Length extension attack" and "Hash-based message authentication code" on wikipedia. In short, naive constructions can be dangerously insecure. Use hash_hmac if available or reimplement HMAC properly without shortcuts.
up
-8
Shane Allen
16 years ago
From the documentation on Digest::MD5:
md5($data,...)
This function will concatenate all arguments, calculate the MD5 digest of this "message", and return it in binary form.

md5_hex($data,...)
Same as md5(), but will return the digest in hexadecimal form.

PHP's function returns the digest in hexadecimal form, so my guess is that you're using md5() instead of md5_hex(). I have verified that md5_hex() generates the same string as PHP's md5() function.

(original comment snipped in various places)
>Hexidecimal hashes generated with Perl's Digest::MD5 module WILL
>NOT equal hashes generated with php's md5() function if the input
>text contains any non-alphanumeric characters.
>
>$phphash = md5('pa$$');
>echo "php original hash from text: $phphash";
>echo "md5 hash from perl: " . $myrow['password'];
>
>outputs:
>
>php original hash from text: 0aed5d740d7fab4201e885019a36eace
>hash from perl: c18c9c57cb3658a50de06491a70b75cd
up
-12
terry _at_ scribendi_com
14 years ago
Do not use the hex strings returned by md5() as a key for MCrypt 256-bit encryption.  Hex characters only represent four bits each, so when you take 32 hex characters, you are only really using a 128-bit key, not a 256-bit one. 

Using an alphanumeric key generator [A-Za-z0-9] will also only provide a 192-bit key in 32 characters.

Two different MD5s concatenated in raw binary form, or mcrypt_create_iv(32,MCRYPT_DEV_RANDOM) will give you a true 256-bit key string.
up
-21
dionyziz at deviantart dot com
11 years ago
Sometimes it's useful to get the actual, binary, md5 digest.
You can use this function for it:

<?php

function md5bin( $target ) {
   
$md5 = md5( $target );
   
$ret = '';

    for (
$i = 0; $i < 32; $i += 2 ) {
       
$ret .= chr( hexdec( $md5{ $i + 1 } ) + hexdec( $md5{ $i } ) * 16 );
    }

    return
$ret;
}

?>
up
-22
John
9 years ago
If you want to hash a large amount of data you can use the hash_init/hash_update/hash_final functions.

This allows you to hash chunks/parts/incremental or whatever you like to call it.
To Top