Detailed explanation of PHP data encryption_PHP tutorial

Data encryption has become more and more important in our lives, especially considering the large number of transactions that occur on the Internet and the large amount of data transmitted. If you are interested in adopting security measures, you will also be interested in learning about the series of security features provided by PHP. In this article, we will introduce these functions and provide some basic usage so that you can add security functions to your application software.

Preliminary knowledge
Before introducing the security functions of PHP in detail, we need to take some time to introduce some basic knowledge about cryptography to readers who have not been exposed to this aspect. If you are already very familiar with the basic concepts of cryptography, you can skip this part. .

Cryptozoology can be popularly described as the study and experiment of encryption/decryption. Encryption is the process of converting easy-to-understand data into difficult-to-understand data, and decryption is the process of converting difficult-to-understand data into original easy-to-understand data. process. Information that is difficult to understand is called a cipher, and information that is easy to understand is called a plaintext.
Encryption/decryption of data requires certain algorithms. These algorithms can be very simple, such as the famous Caesar code, but current encryption algorithms are relatively more complex, and some of them are even undecipherable using existing methods.

PHP’s encryption function
Anyone who has a little experience using non-Windows platforms may be familiar with crypt(). This function completes a function called one-way encryption. It can encrypt some plain codes, but it cannot convert the password into the original plain code. Although this may seem like a useless feature on the surface, it is widely used to ensure the integrity of system passwords. Because once the one-way encrypted password falls into the hands of a third party, it cannot be restored to plain text, so it is of little use. When verifying the password entered by the user, the user's input also uses a one-way algorithm. If the input matches the stored encrypted password, the entered password must be correct.

PHP also provides the possibility to use its crypt() function to complete one-way encryption. I'll briefly introduce the function here:
string crypt (string input_string [, string salt])
The input_string parameter is the string that needs to be encrypted, and the second optional salt is a bit string that can affect the encrypted password, further ruling out the possibility of what is called a precomputation attack. By default, PHP uses a 2-character DES interference string. If your system uses MD5 (I will introduce the MD5 algorithm later), it will use a 12-character interference string. By the way, you can discover the length of the interference string your system will use by executing the following command:
print "My system salt size is: ". CRYPT_SALT_LENGTH;
The system may also support other encryption algorithms. crypt() supports four algorithms. The following are the algorithms it supports and the length of the corresponding salt parameters:

Algorithm Salt length
CRYPT_STD_DES 2-character (Default)
CRYPT_EXT_DES 9-character
CRYPT_MD5 12-character beginning with $
CRYPT_BLOWFISH 16-character beginning with $
Use crypt() to implement user authentication
As an example of the crypt() function, consider a situation where you wish to create a PHP script that restricts access to a directory to only users who can provide the correct username and password. I will store the data in a table in MySQL, my favorite database.
Let's start our example by creating this table called members:
mysql>CREATE TABLE members (
->username CHAR(14) NOT NULL,
->password CHAR(32) NOT NULL,
->PRIMARY KEY(username)
->);
Then, we assume that the following data is already stored in the table:
Username Password
clark keloD1C377lKE
bruce ba1T7vnz9AWgk
peter paLUvRWsRLZ4U
The plain codes corresponding to these encrypted passwords are kent, banner and parker respectively. Pay attention to the first two letters of each password. This is because I used the following code to create a interference string based on the first two letters of the password:
$enteredPassword.
$salt = substr($enteredPassword, 0, 2);
$userPswd = crypt($enteredPassword, $salt);
// $userPswd is then stored in MySQL together with the username
I will be using Apache's password-response authentication configuration to prompt the user for a username and password. A little-known fact about PHP is that it recognizes usernames and passwords entered by the Apache password-response system as $PHP_AUTH_USER and $PHP_AUTH_PW. I will use these two variables in the authentication script. Take some time to read the script below carefully and pay more attention to the explanations to better understand the code below:
Application of crypt() and Apache's password-response verification system
$host = "http://www.jnwebseo.com";
$user = "zorro";
$pswd = "hell odolly";
$db = "users";
// Set authorization to False
$authorization = 0;
// Verify that user has entered username and password
if (isset($PHP_AUTH_USER) &&isset($PHP_AUTH_PW)) :
mysql_pconnect($host, $user, $pswd) or die("Can't connect to MySQL
server!");
mysql_select_db($db) or die("Can't select database!");
// Perform the encryption
$salt = substr($PHP_AUTH_PW, 0, 2);
$encrypted_pswd = crypt($PHP_AUTH_PW, $salt);
// Build the query
$query = "SELECT username FROM members WHERE
username = '$PHP_AUTH_USER' AND
password = '$encrypted_pswd'";
// Execute the query
if (mysql_numrows(mysql_query($query)) == 1) :
$authorization = 1;
endif;
endif;
// confirm authorization
if (! $authorization) :
header('WWW-Authenticate: Basic realm="Private"');
header('HTTP/1.0 401 Unauthorized');
print "You are unauthorized to enter this area.";
exit;
else :
print "This is the secret data!";
endif;
>
The above is a simple authentication system to verify user access rights. When using crypt() to protect important confidential information, remember that crypt() used by default is not the most secure and can only be used in systems with lower security requirements. If higher security is required Performance requires the algorithm I introduce later in this article.
Next I will introduce another function supported by PHP━━md5(). This function uses the MD5 hash algorithm. It has several interesting uses worth mentioning:

Mixed
A hash function transforms a variable-length message into a fixed-length hashed output, also known as a "message digest". This is useful because a fixed-length string can be used to check file integrity and verify digital signatures and user authentication. As it is suitable for PHP, PHP's built-in md5() hash function will convert a variable-length message into a 128-bit (32-character) message digest. An interesting feature of mixed encoding is that the original plain code cannot be obtained by analyzing the mixed information, because the mixed result has no dependence on the original plain code content. Even changing only one character in a string will cause the MD5 hybrid algorithm to calculate two completely different results. Let’s first look at the contents of the table below and its corresponding results:
Use md5() to mix strings
$msg = "This is some message that I just wrote";
$enc_msg = md5($msg);
print "hash: $enc_msg ";
>
Result:
hash: 81ea092649ca32b5ba375e81d8f4972c
Note that the result is 32 characters long. Let’s take a look at the table below. The value of $msg has changed slightly:
Use md5() to shuffle a slightly changed string
//Note that there is one s
missing in message $msg = "This is some mesage that I just wrote";
$enc_msg = md5($msg);
print "hash2: $enc_msg
";
>
Result:
hash2: e86cf511bd5490d46d5cd61738c82c0c
It can be found that although the length of both results is 32 characters, a small change in the plaintext causes a big change in the result. Therefore, the hashing and md5() functions are a good way to check small changes in the data. tools.
Although crypt() and md5() have their uses, both are subject to certain limitations in functionality. In the following sections, we will introduce two very useful PHP extensions called Mcrypt and Mhash, which will greatly expand the encryption options for PHP users.
Although we have explained the importance of one-way encryption in the above section, sometimes we may need to restore the password data to the original data after encryption. Fortunately, PHP provides this in the form of the Mcrypt extension library possibility.
Mcrypt
Mcrypt 2.5.7 Unix | Win32
Mcrypt 2.4.7 is a powerful encryption algorithm extension library, which includes 22 algorithms, including the following algorithms:
Blowfish RC2 Safer-sk64 xtea
Cast-256 RC4 Safer-sk128
DES RC4-iv Serpent
Enigma Rijndael-128 Threeway
Gost Rijndael-192 TripleDES
LOKI97 Rijndael-256 Twofish
PanamaSaferplus Wake

Installation:
Mcrypt is not included in the standard PHP software package, so you need to download it. The download address is: ftp://argeas.cs-net.gr/pub/unix/mcrypt/. After downloading, compile it as follows and expand it in PHP:
Download the Mcrypt package.
gunzipmcrypt-x.x.x.tar.gz
tar -xvfmcrypt-x.x.x.tar
./configure --disable-posix-threads
make
make install
cd to your PHP directory.
./configure -with-mcrypt=[dir] [--other-configuration-directives]
make
make install
Of course, depending on your requirements and the relationship between PHP installation and the Internet server software, the above process may need to be modified appropriately.

Use Mcrypt
The advantage of Mcrypt is not only that it provides many encryption algorithms, but also that it can encrypt/decrypt data. In addition, it also provides 35 functions for processing data. Although a detailed introduction to these functions is beyond the scope of this article, I will give a brief introduction to a few typical functions.

First, I will introduce how to use the Mcrypt extension library to encrypt data, and then how to use it to decrypt. The following code demonstrates this process. It first encrypts the data, then displays the encrypted data on the browser, restores the encrypted data to the original string, and displays it on the browser.
Use Mcrypt to encrypt and decrypt data
// Designate string to be encrypted
$string = "Applied Cryptography, by Bruce Schneier, is
a wonderful cryptography reference.";
// Encryption/decryption key
$key = "Four score and twenty years ago";
// Encryption Algorithm
$cipher_alg = MCRYPT_RIJNDAEL_128;
// Create the initialization vector for added security.
$iv = mcrypt_create_iv(mcrypt_get_iv_size($cipher_alg,
MCRYPT_MODE_ECB), MCRYPT_RAND);
// Output original string
print "Original string: $string
";
// Encrypt $string
$encrypted_string = mcrypt_encrypt($cipher_alg, $key,
$string, MCRYPT_MODE_CBC, $iv);
// Convert to hexadecimal and output to browser
print "Encrypted string: ".bin2hex($encrypted_string)."
";
$decrypted_string = mcrypt_decrypt($cipher_alg, $key,
$encrypted_string, MCRYPT_MODE_CBC, $iv);
print "Decrypted string: $decrypted_string";
>
Executing the above script will produce the following output:
Original string: Applied Cryptography, by Bruce Schneier, is a wonderful cryptography reference.
Encrypted string: 02a7c58b1ebd22a9523468694b091e60411cc4dea8652bb8072 34fa06bbfb20e71ecf525f29df58e28f3d9bf541f7ebcecf62b c89fde4d8e7ba1e6cc9ea2485047 8c11742f5cfa1d23fe22fe8 bfbab5e
Decrypted string: Applied Cryptography, by Bruce Schneier, is a wonderful cryptography reference.
The two most typical functions in the above code are mcrypt_encrypt() and mcrypt_decrypt(), and their uses are obvious. I used the "Telegraph Codebook" mode. Mcrypt offers several encryption methods. Since each encryption method has specific characters that can affect the security of the password, each mode needs to be understood. For readers who have no contact with cryptosystems, the mcrypt_create_iv() function may be more interesting. Although a thorough explanation of this function is beyond the scope of this article, I will still mention the initialization vector it creates. (hence, iv), this vector can make each piece of information independent of each other. Although not all modes require this initialization variable, PHP will issue a warning message if this variable is not provided in the required mode.

Mhash extension library
http://sourceforge.net/projects/mhash/
The Mhash extension library of version 0.8.3 supports 12 mixing algorithms. A careful inspection of the header file mhash.h of Mhash v.0.8.3 shows that it supports the following mixing algorithms:
CRC32 HAVAL160 MD5
CRC32B HAVAL192 RIPEMD160
GOST HAVAL224 SHA1
HAVAL128 HAVAL256 TIGER

Installation
Like Mcrypt, Mhash is not included in the PHP package. For non-Windows users, here is the installation process:
Download Mhash extension library
gunzipmhash-x.x.x.tar.gz
tar -xvfmhash-x.x.x.tar
./configure
make
make install
cd
./configure -with-mhash=[dir] [--other-configuration-directives]
make
make install
Like Mcrypt, additional configuration of Mhash may be required depending on how PHP is installed on the Internet server software.
For Windows users, there is a good PHP package including the Mhash extension library at http://www.php4win.de. Just download and unzip it, and then install it according to the instructions in the readme.first document.

Use Mhash
Mixing information is very simple, take a look at the following example:
$hash_alg = MHASH_TIGER;
$message = "These are the directions to the secret fort. Two steps left, three steps right, and cha chacha.";
$hashed_message = mhash($hash_alg, $message);
print "The hashed message is ". bin2hex($hashed_message);
>
Executing this script will result in the following output:
The hashed message is 07a92a4db3a4177f19ec9034ae5400eb60d1a9fbb4ade461
The purpose of using the bin2hex() function here is to facilitate our understanding of the output of $hashed_message. This is because the mixed result is in binary format. In order to convert it into an easy-to-understand format, it must be converted into hexadecimal format. .
It is important to note that shuffling is a one-way function and its results do not depend on input, so this information can be displayed publicly. This policy is typically used to allow users to compare downloaded files with files provided by the system administrator to ensure file integrity.
Mhash has some other useful functions. For example, I need to output the name of an algorithm supported by Mhash. Since the names of all algorithms supported by Mhash start with MHASH_, this task can be completed by executing the following code:
$hash_alg = MHASH_TIGER;
print "This data has been hashed with the".mhash_get_hash_name($hashed_message)."hashing algorithm.";
>
The resulting output is:
This data has been hashed with the TIGER hashing algorithm.
One last thing to note about PHP and encryption
One final important thing to note about PHP and encryption is that the data transferred between the server and client is not secure in transit! PHP is a server-side technology and cannot prevent data from being leaked during transmission. Therefore, if you want to implement a complete secure application, it is recommended to use Apache-SSL or other secure server arrangements.

Conclusion
This article introduces one of PHP's most useful features - data encryption. It not only discusses PHP's built-in crypt() and md5() encryption functions, but also discusses powerful extension libraries for data encryption - Mcrypt and Mhash. At the end of this article, I need to point out that a truly secure PHP application should also include a secure server. Since PHP is a server-side technology, it cannot Ensure data security.