How to escape/strip special characters in the LaTeX document?

Question

We implemented the online service where it is possible to generate PDF with predefined structure. The user can choose a LaTeX template and then compile it with an appropriate inputs.

The question we worry about is the security, that the malicious user was not able to gain shell access through the injection of special instruction into latex document.

We need some workaround for this or at least a list of special characters that we should strip from the input data.

Preferred language would be PHP, but any suggestions, constructions and links are very welcomed.

PS. in few word we're looking for mysql_real_escape_string for LaTeX

Answer 1

Here's some code to implement the Geoff Reedy answer. I place this code in the public domain.

<?

$test = "Test characters: # $ % & ~ _ ^ \ { }.";
header( "content-type:text/plain" );
print latexSpecialChars( $test );
exit;

function latexSpecialChars( $string )
{
    $map = array( 
            "#"=>"\\#",
            "$"=>"\\$",
            "%"=>"\\%",
            "&"=>"\\&",
            "~"=>"\\~{}",
            "_"=>"\\_",
            "^"=>"\\^{}",
            "\\"=>"\\textbackslash",
            "{"=>"\\{",
            "}"=>"\\}",
    );
    return preg_replace( "/([\^\%~\\\\#\$%&_\{\}])/e", "\$map['$1']", $string );
}