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Independent Verification of IPsec Functionality in FreeBSD
<email>honig@sprynet.com</email>
<personname><firstname>David</firstname><surname>Honig</surname></personname><affiliation> <_:address-1/> </affiliation>
1999-05-03
FreeBSD is a registered trademark of the FreeBSD Foundation.
Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this document, and the FreeBSD Project was aware of the trademark claim, the designations have been followed by the <quote>™</quote> or the <quote>®</quote> symbol.
$FreeBSD: head/en_US.ISO8859-1/articles/ipsec-must/article.xml 52227 2018-09-06 01:30:47Z ebrandi $
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, lets assume you have <link linkend="ipsec-install"> installed <emphasis>IPsec</emphasis></link>. How do you know it is <link linkend="caveat">working</link>? Sure, your connection will not work if it is misconfigured, and it will work when you finally get it right. <citerefentry><refentrytitle>netstat</refentrytitle><manvolnum>1</manvolnum></citerefentry> 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 <quote>encrypted mode</quote> was not encrypted---as the outermost IP header must be if the packet is to be routable.
MUST
Ueli Maurer's <quote>Universal Statistical Test for Random Bit Generators</quote>(<link xlink:href="https://web.archive.org/web/20011115002319/http://www.geocities.com/SiliconValley/Code/4704/universal.pdf"> <acronym>MUST</acronym></link>) quickly measures the entropy of a sample. It uses a compression-like algorithm. <link linkend="code">The code is given below</link> 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 <citerefentry><refentrytitle>tcpdump</refentrytitle><manvolnum>1</manvolnum></citerefentry> lets you do this, if you have enabled the <emphasis>Berkeley Packet Filter</emphasis> interface in your <link linkend="kernel">kernel's config file</link>.
The command:
ComponentTranslation
This translation Translated FreeBSD Doc/articles_ipsec-must Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
The following strings have the same context and source.
Translated FreeBSD Doc/articles_new-users Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/books_faq Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/articles_pam Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/articles_explaining-bsd Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/books_handbook Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/articles_fonts Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/books_developers-handbook Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/articles_vm-design Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.
Translated FreeBSD Doc/articles_freebsd-questions Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.

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Source string comment
(itstool) path: legalnotice/para
Flags
read-only
Source string location
article.translate.xml:21
String age
a year ago
Source string age
a year ago
Translation file
articles/ipsec-must.pot, string 7