PHP - Manual: md5

2024-12-30

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md5

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

md5 — 计算字符串的 MD5 散列值

警告

由于此函数依赖的算法已不足够复杂,不推荐使用此函数对明文密码加密。详细内容参见这里。

说明

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

使用 » RSA 数据安全公司的 MD5 消息摘要算法计算 string 的 MD5 散列值，并返回该散列值。

参数

string: 要计算的字符串。
binary: 如果可选的 binary 被设置为 true，那么 md5 摘要将以 16 字符长度的原始二进制格式返回。

返回值

以 32 字符的十六进制数形式返回散列值。

范例

示例 #1 md5() 范例


<?php
$str = 'apple';

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

参见

md5_file() - 计算指定文件的 MD5 散列值
sha1_file() - 计算文件的 sha1 散列值
crc32() - 计算一个字符串的 crc32 多项式
sha1() - 计算字符串的 sha1 散列值
hash() - 生成哈希值（消息摘要）
crypt() - 单向字符串散列
password_hash() - 创建密码的散列（hash）

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User Contributed Notes 9 notes

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Ray.Paseur sometimes uses Gmail ¶

3 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.

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-2

yiminrong at yahoo dot ca ¶

1 year ago


Regarding Ray Paseur's comment, the strings hash to:

0e462097431906509019562988736854
0e830400451993494058024219903391

The odds of getting a hash exactly matching the format /^0+e[0-9]+$/ are not high but are also not negligible.

It should be added as a general warning for all hash functions to always use the triple equals === for comparison.

Actually, the warning should be in the operators section when comparing string values! There are lots of warnings about string comparisons, but nothing specific about the format /^0+e[0-9]+$/.

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-3

John ¶

12 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.

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-15

Shane Allen ¶

19 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

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-9

Steve M ¶

2 years ago


I've found multiple sites suggesting the code:

md5(file_get_contents($filename));

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!

md5_file($filename);

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)

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-23

radon8472 at radon-software dot net ¶

6 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
?>

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-14

hkmaly ¶

4 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.

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-25

terry _at_ scribendi_com ¶

17 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.

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-59

dionyziz at deviantart dot com ¶

14 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;
}

?>

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官方地址：https://www.php.net/manual/en/function.md5.php

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md5

说明

参数

返回值

范例

参见

User Contributed Notes 9 notes