Common PHP Encryption Methods: MD5, Crypt, SHA1, URL Encoding, Base64, and Password Hashing

PHP provides several encryption approaches that can be grouped into one‑way hash functions, symmetric (reversible) encodings, and asymmetric techniques, each serving different security needs.

MD5 Hash – MD5 is a non‑reversible hash commonly used for password storage. Example:

<?php
// Example string
$str = "this is string";
// MD5 hash (hexadecimal, default)
$res = md5($str);
// MD5 raw binary (16‑byte) output
$res = md5($str, true);
?>

crypt() Function – Another one‑way hash that uses a salt. If no salt is provided, a random one is generated.

<?php
$str = "this is string";
// crypt without explicit salt (randomly generated)
$res = crypt($str);
// crypt with a two‑character salt (e.g., "jm")
$res = crypt($str, 'jm');
?>

SHA1 Hash – Similar to MD5, SHA1 returns a 40‑character hexadecimal string unless the raw output flag is set.

<?php
$str = "this is string";
$res = sha1($str);            // hex output
$res = sha1($str, true);      // raw binary output
?>

URL Encoding – A reversible encoding useful for safely transmitting data in URLs.

<?php
$str = "http://www.baidu.com?name=zhangsan&phone=112";
$res = urlencode($str);   // encode
$result = urldecode($res); // decode
?>

Base64 Encoding – Primarily used for data transport rather than security; it converts binary data to an ASCII string.

base64_encode($data);
base64_decode($data);

hash() Function – Provides a flexible one‑way hash where the algorithm (e.g., "md5", "sha256") is specified as the first argument. hash($algorithm, $data); PHP 5.5+ introduces the Password Hashing API for secure password storage:

$hash = password_hash($password, PASSWORD_DEFAULT, $options);
if (password_verify($password, $hash)) {
    // password is correct
} else {
    // invalid password
}

AES Example Class – Demonstrates a simple wrapper for AES‑128‑ECB encryption/decryption using OpenSSL.

class AES {
    /**
     * Encrypt a string with a secret key.
     */
    public static function encrypt($str, $secret) {
        return base64_encode(openssl_encrypt($str, "AES-128-ECB", $secret, OPENSSL_RAW_DATA));
    }
    /**
     * Decrypt a string with a secret key.
     */
    public static function decrypt($str, $secret) {
        return openssl_decrypt(base64_decode($str), "AES-128-ECB", $secret, OPENSSL_RAW_DATA);
    }
}

These examples illustrate how PHP developers can choose appropriate encryption or hashing mechanisms based on whether they need irreversible protection, reversible encoding, or full cryptographic security.