Dutch PHP Conference 2021 - Call for Papers


(PHP 4, PHP 5, PHP 7, PHP 8)



パスワードを守るためにこの関数を使うことはおすすめしません。 ハッシュアルゴリズムの高速性がその理由です。 詳細とベストプラクティスについては、パスワードハッシュ FAQを参照ください。


md5 ( string $string , bool $binary = false ) : string

» RSA Data Security, Inc. の MD5メッセージダイジェストアルゴリズム を用いて string の MD5 ハッシュ値を計算し、 そのハッシュを返します。





オプションのbinarytrue が指定された場合、 md5 ダイジェストが 16 バイト長のバイナリ形式で返されます。


32 文字の 16 進数からなるハッシュを返します。

例1 md5() の例


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


  • md5_file() - 指定したファイルのMD5ハッシュ値を計算する
  • sha1_file() - ファイルの sha1 ハッシュを計算する
  • crc32() - 文字列の crc32 多項式計算を行う
  • sha1() - 文字列の sha1 ハッシュを計算する
  • hash() - ハッシュ値 (メッセージダイジェスト) を生成する
  • crypt() - 文字列の一方向のハッシュ化を行う
  • password_hash() - パスワードハッシュを作る

add a note add a note

User Contributed Notes 8 notes

Ray.Paseur sometimes uses Gmail
2 years 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.
11 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.
radon8472 at radon-software dot net
4 years ago
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.

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

raw2hex($rawMd5) == md5($post_data)) // Post-Data is okay
else                                    // Post-Data is currupted
Shane Allen
17 years ago
From the documentation on Digest::MD5:
This function will concatenate all arguments, calculate the MD5 digest of this "message", and return it in binary form.

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'];
>php original hash from text: 0aed5d740d7fab4201e885019a36eace
>hash from perl: c18c9c57cb3658a50de06491a70b75cd
3 years 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.
terry _at_ scribendi_com
15 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.
Steve M
1 year ago
I've found multiple sites suggesting the code:


Until recently, I hadn't noticed any issues with this locally... but then I tried to hash a 700MB file, with a 2048MB memory limit and kept getting out of memory errors...

There appears to be a limit to how long a string the md5() function can handle, and the alternative function is likely more memory efficient anyway. I would highly recommend to all who need file hashing (for detecting duplicates, not security digests) use the md5_file() function and NOT the regular string md5() function!


Note, to those interested, as this was for a local application not a server, I was more concerned with results than memory efficiency. In a live environment, you would never want to read an entire file into memory at once when avoidable. (at the time of coding, I did not know of the alternative function)
dionyziz at deviantart dot com
13 years ago
Sometimes it's useful to get the actual, binary, md5 digest.
You can use this function for it:


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

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


To Top