diff --git a/en_US.ISO8859-1/articles/ipsec-must/article.sgml b/en_US.ISO8859-1/articles/ipsec-must/article.sgml index 716ce5df5b..34edb9c5c5 100644 --- a/en_US.ISO8859-1/articles/ipsec-must/article.sgml +++ b/en_US.ISO8859-1/articles/ipsec-must/article.sgml @@ -1,297 +1,297 @@ Independent Verification of IPSec Functionality in FreeBSD

Independent Verification of IPsec Functionality Under FreeBSD 3.0

You installed IPsec and it seems to be working. How do you know? I describe a method for experimentally verifying that IPsec is working

The Problem

First, let's assume you have installed IPsec. How do you know its working? Sure, your connection won't work if its misconfigured, and it will work when you finally get it right. Netstat will list it. But can you independently confirm it?

The Solution

First, some crypto-relevent info theory:

Encrypted data is uniformly distributed, ie, has maximal entropy per symbol.
Raw, uncompressed data is typically redundant, i.e., has sub-maximal entropy.

Suppose you could measure the entropy of the data to- and from- your network interface. Then you could see the difference between unencrypted data and encrypted data. This would be true even if some of the data in "encrypted mode" was not encrypted ---as the outermost IP header must be, if the packet is to be routable.

MUST

Ueli Maurer's "Universal Statistical Test for Random Bit Generators" ("MUST") quickly measures the entropy of a sample. It uses a compression-like algorithm. The code is given below for a variant which measures successive (~quarter megabyte) chunks of a file.

Tcpdump

We also need a way to capture the raw network data. A program called "tcpdump" lets you do this, if you have enabled the Berkeley Packet Filter interface in your kernel's config file.

+ href="#KERNELNAME">kernel's config file.

The command

tcpdump -c 4000 -s 10000 -w dumpfile.bin

will capture 4000 raw packets to dumpfile.bin. Up to 10,000 bytes per packet will be captured in this example.

The Experiment

Here's the experiment. Open a window to an IPsec host and another window to an insecure host.

Now start capturing packets.

In the "secure" window, run the unix command "yes", which will stream the "y" character. After a while, stop this. Switch to the insecure window, and repeat. After a while, stop.

Now run MUST on the captured packets. You should see something like the the following. The important thing to note is that the secure connection has 93% (6.7) of the expected value (7.18), and the "normal" connection has 29% (2.1) of the expected value.

% tcpdump -c 4000 -s 10000 -w ipsecdemo.bin
 % uliscan ipsecdemo.bin
 
 Uliscan 21 Dec 98
 L=8 256 258560
 Measuring file ipsecdemo.bin
 Init done
 Expected value for L=8 is 7.1836656
 6.9396 --------------------------------------------------------
 6.6177 -----------------------------------------------------
 6.4100 ---------------------------------------------------
 2.1101 -----------------
 2.0838 -----------------
 2.0983 -----------------

Caveat

This experiment shows that IPsec does seem to be distributing the payload data uniformly, as encryption should. However, the experiment described here can not detect many possible flaws in a system (none of which do I have any evidence for). These include poor key generation or exchange, data or keys being visible to others, use of weak algorithms, kernel subversion, etc. Study the source; know the code.

IPsec -Definition

Internet Protocol security extensions to IP v 4; required for IP v6. A protocol for negotiating encryption and authentication at the IP (host-to-host) level. SSL secures only one application socket; SSH secures only a login; PGP secures only a specified file or message. IPsec encrypts everything between two hosts.

Installing IPsec

Starting from the BSD 3.0 stable release,

install IPsec v0.04, rebuild, reinstall
run the administration tools (e.g, ipsecadm) and distribute keys (or use Photuris for key exchange)
set the routes (rt) up appropriately

You may want to make an "ipsec_setup" script containing the ipsecadm and rt commands which establish your IPsec tunnel. You can run this script automatically at boottime from your /etc/rc.local The ipsec_setup script will have to contain at least two ipsecadm commands and one rt command to be useful.

usr/src/sys/i386/conf/KERNELNAME

This needs to be present in the kernel config file in order to run IPsec. After adding it, run config, etc. and rebuild and reinstall.

# The `bpfilter' pseudo-device enables the Berkeley Packet Filter. Be
 # aware of the legal and administrative consequences of enabling this
 # option. Heh heh. The number of devices determines the maximum number of
 # simultaneous BPF clients programs runnable.
 pseudo-device bpfilter 2 #Berkeley packet filter
 
 # IPSEC
 options IPSEC
 options "MD5"
 pseudo-device enc 1

Maurer's Universal Statistical Test (for block +

Maurer's Universal Statistical Test (for block size=8 bits)


 #include 
 
 int main(argc, argv)
 int argc;
 char **argv;
 {
   FILE *fptr;
   int i,j;
   int b, c;
   int table[V];
   double sum = 0.0;
   int iproduct = 1;
   int run;
 
   extern double   log(/* double x */);
 
   printf("Uliscan 21 Dec 98 \nL=%d %d %d \n", L, V, MAXSAMP);
 
   if (argc < 2) {
     printf("Usage: Uliscan filename\n");
     exit(-1);
   } else {
     printf("Measuring file %s\n", argv[1]);
   }
 
   fptr = fopen(argv[1],"rb");
 
   if (fptr == NULL) {
     printf("Can't find %s\n", argv[1]);
     exit(-1);
   }
 
   for (i = 0; i < V; i++) {
     table[i] = 0;
   }
 
   for (i = 0; i < Q; i++) {
     b = fgetc(fptr);
     table[b] = i;
   }
 
   printf("Init done\n");
 
   printf("Expected value for L=8 is 7.1836656\n");
 
   run = 1;
 
   while (run) {
     sum = 0.0;
     iproduct = 1;
 
     if (run)
       for (i = Q; run && i < Q + K; i++) {
         j = i;
         b = fgetc(fptr);
 
         if (b < 0)
           run = 0;
 
         if (run) {
           if (table[b] > j)
             j += K;
 
           sum += log((double)(j-table[b]));
 
           table[b] = i;
         }
       }
 
     if (!run)
       printf("Premature end of file; read %d blocks.\n", i - Q);
 
     sum = (sum/((double)(i - Q))) /  log(2.0);
     printf("%4.4f ", sum);
 
     for (i = 0; i < (int)(sum*8.0 + 0.50); i++)
       printf("-");
 
     printf("\n");
 
     /* refill initial table */
     if (0) {
       for (i = 0; i < Q; i++) {
         b = fgetc(fptr);
         if (b < 0) {
           run = 0;
         } else {
           table[b] = i;
         }
       }
     }
   }
 }]]>

diff --git a/en_US.ISO_8859-1/articles/ipsec-must/article.sgml b/en_US.ISO_8859-1/articles/ipsec-must/article.sgml index 716ce5df5b..34edb9c5c5 100644 --- a/en_US.ISO_8859-1/articles/ipsec-must/article.sgml +++ b/en_US.ISO_8859-1/articles/ipsec-must/article.sgml @@ -1,297 +1,297 @@ Independent Verification of IPSec Functionality in FreeBSD