how to decrypt md5 code example

Example: php md5 decrypt

As already stated, you cannot decrypt MD5 without attempting something like brute force hacking which is extremely resource intensive, not practical, and unethical.

However you could use something like this to encrypt / decrypt passwords/etc safely:

$input = "SmackFactory";

$encrypted = encryptIt( $input );
$decrypted = decryptIt( $encrypted );

echo $encrypted . '<br />' . $decrypted;

function encryptIt( $q ) {
    $cryptKey  = 'qJB0rGtIn5UB1xG03efyCp';
    $qEncoded      = base64_encode( mcrypt_encrypt( MCRYPT_RIJNDAEL_256, md5( $cryptKey ), $q, MCRYPT_MODE_CBC, md5( md5( $cryptKey ) ) ) );
    return( $qEncoded );
}

function decryptIt( $q ) {
    $cryptKey  = 'qJB0rGtIn5UB1xG03efyCp';
    $qDecoded      = rtrim( mcrypt_decrypt( MCRYPT_RIJNDAEL_256, md5( $cryptKey ), base64_decode( $q ), MCRYPT_MODE_CBC, md5( md5( $cryptKey ) ) ), "\0");
    return( $qDecoded );
}
Using a encypted method with a salt would be even safer, but this would be a good next step past just using a MD5 hash.