Encrypting/decrypting without mcrypt

It is a little-known fact among members of the general PHP community that the mcrypt extension, the core of most PHP-based encryption considered secure, is anything but secure. One of the biggest issues, from a security perspective, is that the mcrypt extension requires advanced knowledge of cryptography to successfully operate, which few programmers have. This leads to gross misuse and ultimately problems such as a 1 in 256 chance of data corruption. Not good odds. Furthermore, developer support for libmcrypt, the core library upon which the mcrypt extension is based, was abandoned in 2007, which means the code base is out-of-date, bug-ridden, and has no mechanism to apply patches. Accordingly, it is extremely important to understand how to perform strong encryption/decryption without using mcrypt!

How to do it...

The solution to the problem posed previously, in case you're wondering, is to use openssl. This extension is well maintained, and has modern and very strong encryption/decryption capabilities.
Tip
Important
In order to use any openssl* functions, the openssl PHP extension must be compiled and enabled! In addition, you will need to install the latest OpenSSL package on your web server.
First, you will need to determine which cipher methods are available on your installation. For this purpose, you can use the openssl_get_cipher_methods() command. Examples will include algorithms based on Advanced Encryption Standard (AES), BlowFish (BF), CAMELLIA, CAST5, Data Encryption Standard (DES), Rivest Cipher (RC) (also affectionately known as Ron's Code), and SEED. You will note that this method shows cipher methods duplicated in upper and lowercase.

Next, you will need to figure out which method is most appropriate for your needs. Here is a table that gives a quick summary of the various methods:

Method	Published	Key size (bits)	Key block size (bytes)	Notes
`camellia`	2000	128, 192, 256	16	Developed by Mitsubishi and NTT
`aes`	1998	128, 192, 256	16	Developed by Joan Daemen and Vincent Rijmen. Originally submitted as Rijndael
`seed`	1998	128	16	Developed by the Korea Information Security Agency
`cast5`	1996	40 to 128	8	Developed by Carlisle Adams and Stafford Tavares
`bf`	1993	1 to 448	8	Designed by Bruce Schneier
`rc2`	1987	8 to 1,024 defaults to 64	8	Designed by Ron Rivest (one of the core founders of RSA)
`des`	1977	56 (+8 parity bits)	8	Developed by IBM, based on work done by Horst Feistel

Another consideration is what your preferred block cipher mode of operation is. Common choices are summarized in this table:

Mode	Stands For	Notes
ECB	Electronic Code Book	Does not require initialization vector (IV); supports parallelization for both encryption and decryption; simple and fast; does not hide data patterns; not recommended!!!
CBC	Cipher Block Chaining	Requires IV; subsequent blocks, even if identical, are XOR'ed with previous block, resulting in better overall encryption; if the IVs are predictable, the first block can be decoded, leaving remaining message exposed; message must be padded to a multiple of the cipher block size; supports parallelization only for decryption
CFB	Cipher Feedback	Close relative of CBC, except that encryption is performed in reverse
OFB	Output Feedback	Very symmetrical: encrypt and decrypt are the same; does not supports parallelization at all
CTR	Counter	Similar in operation to OFB; supports parallelization for both encryption and decryption
CCM	Counter with CBC-MAC	Derivative of CTR; only designed for block length of 128 bits; provides authentication and confidentiality; CBC-MAC stands for Cipher Block Chaining - Message Authentication Code
GCM	Galois/Counter Mode	Based on CTR mode; should use a different IV for each stream to be encrypted; exceptionally high throughput (compared to other modes); supports parallelization for both encryption and decryption
XTS	XEX-based Tweaked-codebook mode with ciphertext Stealing	Relatively new (2010) and fast; uses two keys; increases the amount of data that can be securely encrypted as one block

Before choosing a cipher method and mode, you will also need to determine whether the encrypted contents needs to be unencrypted outside of your PHP application. For example, if you are storing database credentials encrypted into a standalone text file, do you need to have the ability to decrypt from the command line? If so, make sure that the cipher method and operation mode you choose are supported by the target operating system.
The number of bytes supplied for the IV varies according to the cipher method chosen. For best results, use random_bytes() (new in PHP 7), which returns a true CSPRNG sequence of bytes. The length of the IV varies considerably. Try a size of 16 to start with. If a warning is generated, the correct number of bytes to be supplied for that algorithm will be shown, so adjust the size accordingly:
```
$iv  = random_bytes(16);
```

To perform encryption, use openssl_encrypt(). Here are the parameters that should be passed:

Parameter	Notes
Data	Plain text you need to encrypt.
Method	One of the methods you identified using `openssl_get_cipher_methods()`. identified as follows: method - key_size - cipher_mode So, for example, if you want a method of AES, a key size of 256, and GCM mode, you would enter `aes-256-gcm`.
Password	Although documented as password, this parameter can be viewed as a key. Use `random_bytes()` to generate a key with a number of bytes to match the desired key size.
Options	Until you gain more experience with `openssl` encryption, it is recommended you stick with the default value of `0`.
IV	Use `random_bytes()` to generate an IV with a number of bytes to match the cipher method.

As an example, suppose you wanted to choose the AES cipher method, a key size of 256, and XTS mode. Here is the code used to encrypt:

$plainText = 'Super Secret Credentials';
$key = random_bytes(16);
$method = 'aes-256-xts';
$cipherText = openssl_encrypt($plainText, $method, $key, 0, $iv);

To decrypt, use the same values for $key and $iv, along with the openssl_decrypt() function:
```
$plainText = openssl_decrypt($cipherText, $method, $key, 0, $iv);
```

How it works...

In order to see which cipher methods are available, create a PHP script called chap_12_openssl_encryption.php and run this command:

<?php
echo implode(', ', openssl_get_cipher_methods());

The output should look something like this:

Next, you can add values for the plain text to be encrypted, the method, key, and IV. As an example, try AES, with a key size of 256, using the XTS operating mode:

$plainText = 'Super Secret Credentials';
$method = 'aes-256-xts';
$key = random_bytes(16);
$iv  = random_bytes(16);

To encrypt, you can use openssl_encrypt(), specifying the parameters configured previously:

$cipherText = openssl_encrypt($plainText, $method, $key, 0, $iv);

You might also want to base 64-encode the result to make it more usable:

$cipherText = base64_encode($cipherText);

To decrypt, use the same $key and $iv values. Don't forget to un-encode the base 64 value first:

$plainText = openssl_decrypt(base64_decode($cipherText), 
$method, $key, 0, $iv);

Here is the output showing the base 64-encoded cipher text, followed by the decrypted plain text:

If you supply an incorrect number of bytes for the IV, for the cipher method chosen, a warning message will be shown:

There's more...

In PHP 7, there was a problem when using open_ssl_encrypt() and open_ssl_decrypt() and the Authenticated Encrypt with Associated Data (AEAD) modes supported: GCM and CCM. Accordingly, in PHP 7.1, three extra parameters have been added to these functions, as follows:

Parameter	Description
`$tag`	Authentication tag passed by reference; variable value remains the same if authentication fails
`$aad`	Additional authentication data
`$tag_length`	4 to 16 for GCM mode; no limits for CCM mode; only for `open_ssl_encrypt()`

For more information, you can refer to https://wiki.php.net/rfc/openssl_aead.

Table of Contents for
PHP 7: Real World Application Development

Encrypting/decrypting without mcrypt

How to do it...

Tip

How it works...

There's more...

See also

Note

Table of Contents for PHP 7: Real World Application Development

Encrypting/decrypting without mcrypt

How to do it...

Tip

How it works...

There's more...

See also

Note

Table of Contents for
PHP 7: Real World Application Development