Independent Verification of IPsec Functionality in FreeBSD
-
-
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, i.e., 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.
-
-
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.
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 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
+
+
+
+%man;
+]>
+
+
+
+ Independent Verification of IPSec Functionality in FreeBSD
+
+
+ David
+ Honig
+
+
+ honig@sprynet.com
+
+
+
+ 3 May 1999
+
+
+ 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
+ it's working? Sure, your
+ connection won't work if its misconfigured, and it will work
+ when you finally get it right. &man.netstat.1; will list it.
+ But can you independently confirm it?
+
+
+
+ The Solution
+
+ First, some crypto-relevant info theory:
+
+
+
+ encrypted data is uniformly distributed, i.e., 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 &man.tcpdump.1; lets you do this, if you have
+ enabled the Berkeley Packet Filter
+ interface in your 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 &man.yes.1;, 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
+ 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.
+
+
+&prompt.user; tcpdump -c 4000 -s 10000 -w ipsecdemo.bin
+&prompt.user; 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 cannotdetect 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 IPv4; required for IPv6. 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
-
-
Most of the modern versions of FreeBSD have IPsec support
- in their base source. So you'll probably will need to
- include IPSEC option in your kernel config
- and, after kernel rebuild and reinstall, configure IPsec
- connections using setkey command.
-
-
-
A comprehensive guide on running IPsec on FreeBSD is
- provided in FreeBSD
- Handbook.
-
-
usr/src/sys/i386/conf/KERNELNAME
-
-
This needs to be present in the kernel config file in order to be able
- to capture network data with tcpdump.
- Be sure to run config after adding this, and rebuild and
- reinstall.
-
-
device bpf
-
-
-
Maurer's Universal Statistical Test (for block
- size=8 bits)
+
+
+
+
+
+ Caveat
+
+ This experiment shows that IPsec does
+ seem to be distributing the payload data
+ uniformly, as encryption should. However,
+ the experiment described here cannot
+ 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 IPv4; required for
+ IPv6. 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
+
+ Most of the modern versions of FreeBSD have IPsec support
+ in their base source. So you'll probably will need to include
+ option in your kernel config and, after
+ kernel rebuild and reinstall, configure IPsec connections using
+ &man.setkey.8; command.
+
+ A comprehensive guide on running IPsec on FreeBSD is
+ provided in FreeBSD
+ Handbook.
+
+
+
+ usr/src/sys/i386/conf/KERNELNAME
+
+ This needs to be present in the kernel config file in order
+ to be able to capture network data with &man.tcpdump.1;. Be sure
+ to run &man.config.8; after adding this, and rebuild and
+ reinstall.
+
+
+device bpf
+
+
+
+
+ Maurer's Universal Statistical Test (for block size=8
+ bits)
+
+ You can find the same code at
+ this link.
+
+
+/*
ULISCAN.c ---blocksize of 8
1 Oct 98
1 Dec 98
21 Dec 98 uliscan.c derived from ueli8.c
This version has // comments removed for Sun cc
This implements Ueli M Maurer's "Universal Statistical Test for Random
Bit Generators" using L=8
Accepts a filename on the command line; writes its results, with other
info, to stdout.
Handles input file exhaustion gracefully.
Ref: J. Cryptology v 5 no 2, 1992 pp 89-105
also on the web somewhere, which is where I found it.
-David Honig
honig@sprynet.com
Usage:
ULISCAN filename
outputs to stdout
*/
#define L 8
-#define V (1<
-#include
+#include <stdio.h>
+#include <math.h>
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) {
+ 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++) {
+ for (i = 0; i < V; i++) {
table[i] = 0;
}
- for (i = 0; i < Q; i++) {
+ 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++) {
+ for (i = Q; run && i < Q + K; i++) {
j = i;
b = fgetc(fptr);
- if (b < 0)
+ if (b < 0)
run = 0;
if (run) {
- if (table[b] > j)
+ 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++)
+ 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++) {
+ for (i = 0; i < Q; i++) {
b = fgetc(fptr);
- if (b < 0) {
+ if (b < 0) {
run = 0;
} else {
table[b] = i;
}
}
}
}
-}]]>