Multilevel Security, Compartments, Covert Channels, Inference Control


Chris Pollett

Oct 24, 2012


Multilevel Security (MLS)

MLS Applications

MLS Security Models

HW Problem

Problem 7.37 Using the info provided with this problem...

(a). Use equation 7.1 to compute the distance: `d(\A\l\i\c\e, \B\o\b)`, `d(\A\l\i\c\e, \C\h\a\r\l\i\e)`, `d(\B\o\b, \C\h\a\r\l\i\e)`.

(b). Assuming the same statistics apply to the shortened iris codes as to normal-lengthed ones, which of the users U,V,W,X,Y is most likely Alice? Bob? Charlie? None of the above?

Answer. To solve this problem, I wrote the following PHP script to dompute all the distances:

//php in xampp is 32 bit
$c['alice'][0]=  0xbe439ad5; // high order half
$c['alice'][1]=  0x98ef5147; // low order half
$c['bob'][0] =   0x9c8b7a14;
$c['bob'][1] =   0x25369584;

$c['u'][0] =     0xc975a213;
$c['u'][1] =     0x2e89ceaf;
$c['v'][0] =     0xdb9a8675;
$c['v'][1] =     0x342fec15;
$c['w'][0] =     0xa6039ad5;
$c['w'][1] =     0xf8cfd965;
$c['x'][0] =     0x1dca7a54;
$c['x'][1] =     0x273497cc;
$c['y'][0] =     0xaf8b6c7d;
$c['y'][1] =     0x5e3f0f9a;

foreach($c as $first_pair => $first_iris_code) {
    foreach($c as $last_pair => $last_iris_code) {
        echo "d($first_pair, $last_pair) = " .
            iris_distance($first_iris_code, $last_iris_code)."\n";

function iris_distance($code1, $code2)

    $score = 0;
    for($k = 0; $k < 2; $k++) {
        for($i = 0; $i< 32; $i++) {
            if (($code1[$k] & 1) != ($code2[$k] & 1)) {
            $code1[$k] = floor($code1[$k]/2);
            $code2[$k] = floor($code2[$k]/2);
    return $score/64;

Using this `d(\A\l\i\c\e, \B\o\b) = 0.453125`, `d(\A\l\i\c\e, \C\h\a\r\l\i\e) = 0.609375`, and `d(\B\o\b, \C\h\a\r\l\i\e) = 0.53125`, answering (a). For (b), `d(u, \C\h\a\r\l\i\e) = 0.171875` so is Charlie, `v` had a score bigger than 0.32 in each case so was no one, `d(w, \A\l\i\c\e) = 0.15625` so `w` is alice, `d(x, \B\o\b) = 0.15625` so `x` is Bob, and `y` did not correspond to anyone.


Bell-LaPadula Idea

McLeans Criticisms of BLP

B and LPs Response

BLP: The Bottom Line

Biba's Model


BLP versus Biba

Comparison of BLP and Bipa


More Compartments

Example Compartments

Compartments Example

MLS vs Compartments

Covert Channel

Covert Channel Example

Covert Channel Example

Covert Channel Example

More Covert Channels

Covert Channel Pervasiveness

Covert Channel Data Rate

Real-World Covert Channel

TCP Frame Parts

Real-World Covert Channel

TCP Covert Messages

Inference Control Example

Inference Control and Research

Naive Inference Control

Less-naive Inference Control