hi it works fine !!
I am make a little adaptation of your code to use with variable

sub chiffrer_string {
        my ($a_chiffrer,$cle) = @_;
        my $key = $cle;
        $key .= "\0" x (16 - length($key));

        my $plain_text = $a_chiffrer;
        $plain_text .= "\0" x (32 - length($a_chiffrer));

        my $cipher = Mcrypt->new( algorithm => 'rijndael-256', mode =>
+ 'ecb' );
        $cipher->init($key, ' 'x32);
        my $encrypted = $cipher->encrypt($plain_text);
        print unpack('H*', $encrypted), $/;
        $cipher->end();
}
[download]

Very thank for your help :)