How to encrypt multiple variables within a php file?

Question

I’m using php to read a file to a $string, he owns some words variables that I need to find and replace with others, that is, I need to get these variables, encrypt them with AES and write again where they were, making a replace.

The variables does not have the same name, and see after the parameter cmd=, the amount of them may vary.

File example with variables:

Inicio
texto=nome?cmd=0a7-5.ext
data...
texto=nome?cmd=12345.ext
data...
texto=nome?cmd=abcd.ext

The value to be replaced is the encrypted variable itself with the following AES:

//fnEncrypt("0a7-5", "1234567890123456");
function fnEncrypt($sValue, $sSecretKey)
{
    return rtrim(
        base64_encode(
            mcrypt_encrypt(
                MCRYPT_RIJNDAEL_256,
                $sSecretKey, $sValue, 
                MCRYPT_MODE_ECB, 
                mcrypt_create_iv(
                    mcrypt_get_iv_size(
                        MCRYPT_RIJNDAEL_256, 
                        MCRYPT_MODE_ECB
                    ), 
                    MCRYPT_RAND)
                )
            ), "\0"
        );
}

What is expected:

Inicio
texto=nome?cmd=dxZIKbLDEtI/m81cEGnB+dVbmy1C+fcIxmeBGHpyYY0=
data...
texto=nome?cmd=+FFzyIqAENF13PnEj5XqpHYlMD2u08uHmWK7HYDyPos=
data...
texto=nome?cmd=cTySfjmfN85GgcWS3aVHSwExC2ZBldBqh9xJq9ndAmc=

How could I replace these variables with their AES encrypted version, knowing that their amount and their values are different?

Answer 1

Assuming it always starts with "?cmd=" and ending at the end of the line, you can use

preg_replace_callback($regex, $callback, $string)

The callback that will be called and passed an array of the elements combined in the string

Regular expression:

/(\?cmd=)(.+)/

Code:

function fnEncrypt($sValue, $sSecretKey)
{
    return rtrim(
        base64_encode(
            mcrypt_encrypt(
                MCRYPT_RIJNDAEL_256,
                $sSecretKey, $sValue, 
                MCRYPT_MODE_ECB, 
                mcrypt_create_iv(
                    mcrypt_get_iv_size(
                        MCRYPT_RIJNDAEL_256, 
                        MCRYPT_MODE_ECB
                    ), 
                    MCRYPT_RAND)
                )
            ), "\0"
        );
}

$string = "
Inicio
texto=nome?cmd=0a7-5.ext
data...
texto=nome?cmd=12345.ext
data...
texto=nome?cmd=abcd.ext
";

function fnEncrypt_match($matches) {
    return $matches[1] . fnEncrypt($matches[2], "1234567890123456");
}

$stringAES = preg_replace_callback('/(\?cmd=)(.+)/', 'fnEncrypt_match', $string);

echo "<pre>
        $stringAES
      </pre>";

Upshot:

Inicio
texto=nome?cmd=dxZIKbLDEtI/m81cEGnB+dVbmy1C+fcIxmeBGHpyYY0=
data...
texto=nome?cmd=+FFzyIqAENF13PnEj5XqpHYlMD2u08uHmWK7HYDyPos=
data...
texto=nome?cmd=cTySfjmfN85GgcWS3aVHSwExC2ZBldBqh9xJq9ndAmc=

---

Heed: the code used to encrypt is not completely secure.
It is recommended to use libsodium.

More information: PHP AES Encrypt / Decrypt