You installed IPsec and it seems to be working. How do you know? I describe a method for experimentally verifying that IPsec is working
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?
First, some crypto-relevent info theory:
Encrypted data is uniformly distributed, ie, has maximal entropy - per symbol.
+encrypted data is uniformly distributed, i.e., has maximal entropy + per symbol;
Raw, uncompressed data is typically redundant, i.e., has +
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 + in "encrypted mode" was not encrypted---as the outermost IP header must be, if the packet is to be routable.
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.
+ (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.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.
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 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 -----------------
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 + 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.
-Internet Protocol security extensions to IP v 4; required for IP v6. A +
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.
Starting from the BSD 3.0 stable release,
+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.
-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.
+A comprehensive guide on running IPsec on FreeBSD is + provided in FreeBSD + Handbook.
This needs to be present in the kernel config file in order to run - IPsec. After adding it, run config, etc. and rebuild and +
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.
-# 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+
device bpf +
You can find the same code at + this link.
+#includeint 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; } } } } }]]>