Independent Verification of IPSec Functionality in FreeBSD

X X Independent Verification of IPSec Functionality in FreeBSD X X X David X Honig X X X

honig@sprynet.com

X X X X 3 May 1999 X X X You installed IPsec and it seems to be working. How do you X know? I describe a method for experimentally verifying that IPsec is X working. X X X X X The Problem X X First, let's assume you have X installed IPsec. How do you know X it's working? Sure, your X connection won't work if its misconfigured, and it will work X when you finally get it right. &man.netstat.1; will list it. X But can you independently confirm it? X X X X The Solution X X First, some crypto-relevant info theory: X X X X encrypted data is uniformly distributed, i.e., has maximal X entropy per symbol; X X X X raw, uncompressed data is typically redundant, i.e., has X sub-maximal entropy. X X X X Suppose you could measure the entropy of the data to- and X from- your network interface. Then you could see the difference X between unencrypted data and encrypted data. This would be true X even if some of the data in encrypted mode was X not encrypted---as the outermost IP header must be, if the X packet is to be routable. X X X MUST X X Ueli Maurer's Universal Statistical Test for Random X Bit Generators( X MUST) quickly measures the entropy X of a sample. It uses a compression-like algorithm. The code is given below for a variant X which measures successive (~quarter megabyte) chunks of a X file. X X X X Tcpdump X X We also need a way to capture the raw network data. A X program called &man.tcpdump.1; lets you do this, if you have X enabled the Berkeley Packet Filter X interface in your kernel's config X file. X X The command X X X tcpdump -c 4000 -s 10000 -w dumpfile.bin X X X will capture 4000 raw packets to X dumpfile.bin. Up to 10,000 bytes per X packet will be captured in this example. X X X X The Experiment X X Here's the experiment. X X X X Open a window to an IPsec host and another window to an X insecure host. X X X X Now start capturing X packets. X X X X In the secure window, run the UNIX X command &man.yes.1;, which will stream the y X character. After a while, stop this. Switch to the X insecure window, and repeat. After a while, stop. X X X X Now run MUST on the X captured packets. You should see something like the X following. The important thing to note is that the secure X connection has 93% (6.7) of the expected value (7.18), and X the normal connection has 29% (2.1) of the X expected value. X X X&prompt.user; tcpdump -c 4000 -s 10000 -w ipsecdemo.bin X&prompt.user; uliscan ipsecdemo.bin X XUliscan 21 Dec 98 XL=8 256 258560 XMeasuring file ipsecdemo.bin XInit done XExpected value for L=8 is 7.1836656 X6.9396 -------------------------------------------------------- X6.6177 ----------------------------------------------------- X6.4100 --------------------------------------------------- X2.1101 ----------------- X2.0838 ----------------- X2.0983 ----------------- X X X X X X X Caveat X X This experiment shows that IPsec does X seem to be distributing the payload data X uniformly, as encryption should. However, X the experiment described here can not X detect many possible flaws in a system (none of which do I have X any evidence for). These include poor key generation or X exchange, data or keys being visible to others, use of weak X algorithms, kernel subversion, etc. Study the source; know the X code. X X X X IPsec---Definition X X Internet Protocol security extensions to IPv4; required for X IPv6. A protocol for negotiating encryption and authentication X at the IP (host-to-host) level. SSL secures only one application X socket; SSH secures only a login; X PGP secures only a specified file or X message. IPsec encrypts everything between two hosts. X X X X Installing IPsec X X Most of the modern versions of FreeBSD have IPsec support X in their base source. So you'll probably will need to include X option in your kernel config and, after X kernel rebuild and reinstall, configure IPsec connections using X &man.setkey.8; command. X X A comprehensive guide on running IPsec on FreeBSD is X provided in FreeBSD X Handbook. X X X X usr/src/sys/i386/conf/KERNELNAME X X This needs to be present in the kernel config file in order X to be able to capture network data with &man.tcpdump.1;. Be sure X to run &man.config.8; after adding this, and rebuild and X reinstall. X X Xdevice bpf X X X X X Maurer's Universal Statistical Test (for block size=8 X bits) X X You can find the same code at X this link. X X X/* X ULISCAN.c ---blocksize of 8 X X 1 Oct 98 X 1 Dec 98 X 21 Dec 98 uliscan.c derived from ueli8.c X X This version has // comments removed for Sun cc X X This implements Ueli M Maurer's "Universal Statistical Test for Random X Bit Generators" using L=8 X X Accepts a filename on the command line; writes its results, with other X info, to stdout. X X Handles input file exhaustion gracefully. X X Ref: J. Cryptology v 5 no 2, 1992 pp 89-105 X also on the web somewhere, which is where I found it. X X -David Honig X honig@sprynet.com X X Usage: X ULISCAN filename X outputs to stdout X*/ X X#define L 8 X#define V (1<<L) X#define Q (10*V) X#define K (100 *Q) X#define MAXSAMP (Q + K) X X#include <stdio.h> X#include <math.h> X Xint main(argc, argv) Xint argc; Xchar **argv; X{ X FILE *fptr; X int i,j; X int b, c; X int table[V]; X double sum = 0.0; X int iproduct = 1; X int run; X X extern double log(/* double x */); X X printf("Uliscan 21 Dec 98 \nL=%d %d %d \n", L, V, MAXSAMP); X X if (argc < 2) { X printf("Usage: Uliscan filename\n"); X exit(-1); X } else { X printf("Measuring file %s\n", argv[1]); X } X X fptr = fopen(argv[1],"rb"); X X if (fptr == NULL) { X printf("Can't find %s\n", argv[1]); X exit(-1); X } X X for (i = 0; i < V; i++) { X table[i] = 0; X } X X for (i = 0; i < Q; i++) { X b = fgetc(fptr); X table[b] = i; X } X X printf("Init done\n"); X X printf("Expected value for L=8 is 7.1836656\n"); X X run = 1; X X while (run) { X sum = 0.0; X iproduct = 1; X X if (run) X for (i = Q; run && i < Q + K; i++) { X j = i; X b = fgetc(fptr); X X if (b < 0) X run = 0; X X if (run) { X if (table[b] > j) X j += K; X X sum += log((double)(j-table[b])); X X table[b] = i; X } X } X X if (!run) X printf("Premature end of file; read %d blocks.\n", i - Q); X X sum = (sum/((double)(i - Q))) / log(2.0); X printf("%4.4f ", sum); X X for (i = 0; i < (int)(sum*8.0 + 0.50); i++) X printf("-"); X X printf("\n"); X X /* refill initial table */ X if (0) { X for (i = 0; i < Q; i++) { X b = fgetc(fptr); X if (b < 0) { X run = 0; X } else { X table[b] = i; X } X } X } X } X} X X X

+ + 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 @@ -98,58 +144,75 @@ 6.4100 --------------------------------------------------- 2.1101 ----------------- 2.0838 ----------------- -2.0983 -----------------

Independent Verification of IPsec Functionality Under FreeBSD 3.0

Independent Verification of IPsec Functionality in FreeBSD

MUST

Tcpdump

IPsec -Definition

IPsec---Definition

Installing IPsec

usr/src/sys/i386/conf/KERNELNAME

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

Caveat

IPsec---Definition

Installing IPsec

usr/src/sys/i386/conf/KERNELNAME

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