Example of PHP getting the MD5 value of a file and determining whether it has been modified

This article mainly introduces an example of PHP obtaining the MD5 value of a file and determining whether it has been modified. Message Digest Algorithm MD5 (Chinese name is Message Digest Algorithm Version 5) is a hash function widely used in the field of computer security. , used to provide message integrity protection. Friends who need it can refer to

Since it is necessary to determine whether the uploaded file has been modified, it is necessary to record the md5 value of the uploaded file. Here is the method of obtaining the md5 value of the file. .

The code is as follows:

if(isset($_FILES['multimedia']) && $_FILES['multimedia']['error']==0)
{
 $file_name = $_FILES['multimedia']['name'];
 $size = getimagesize($_FILES['multimedia']['tmp_name']);
    $type = $_FILES['multimedia']['type'];
 $original = $_FILES['multimedia']['tmp_name'];
 $md5 = md5_file($original);
 echo $md5;
}

md5_file()

md5_file() function calculates the MD5 hash of the file . The md5() function uses RSA data security, including the MD5 message digest algorithm. Returns the calculated MD5 hash on success, false on failure.

Syntax: md5(string,raw)

Parameter string, required. Specifies the file to be calculated.

Parameter charlist, optional. Specifies hexadecimal or binary output format: TRUE - raw 16-character binary format; FALSE - default. 32-character hexadecimal number.

The code is as follows:

<?php
$filename = "test.txt";
$md5file = md5_file($filename);
echo $md5file;
?>

Store the MD5 hash of the "test.txt" file:

The code is as follows:

<?php
$md5file = md5_file("test.txt");
file_put_contents("md5file.txt",$md5file);
?>

In this example, we will detect whether "test.txt" has been changed (that is, whether the MD5 hash has been changed):

Code As follows:

<?php
$md5file = file_get_contents("md5file.txt");
if (md5_file("test.txt") == $md5file)
{
 echo "The file is ok.";
}
else
{
 echo "The file has been changed.";
}
?>

Output:

The code is as follows:

The file is ok.

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