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<a href="<page docs/verifying-signatures>">Verifying Signatures</a>
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<h1>How to verify signatures for packages</h1>
<hr>
<h3>What is a signature and why should I check it?</h3>
<hr>
<p>How do you know that the Tor program you have is really the
one we made? Many Tor users have very real adversaries who might
try to give them a fake version of Tor — and it doesn't matter
how secure and anonymous Tor is if you're not running the real Tor.</p>
<p>An attacker could try a variety of attacks to get you to download
a fake Tor. For example, he could trick you into thinking some other
website is a great place to download Tor. That's why you should
always download Tor from <b>https</b>://www.torproject.org/. The
https part means there's encryption and authentication between your
browser and the website, making it much harder for the attacker
to modify your download. But it's not perfect. Some places in the
world block the Tor website, making users try <a href="<page
docs/faq>#GetTor">somewhere else</a>. Large
companies sometimes force employees to use a modified browser,
so the company can listen in on all their browsing. We've even <a
href="https://blog.torproject.org/blog/diginotar-debacle-and-what-you-should-do-about-it">seen</a>
attackers who have the ability to trick your browser into thinking
you're talking to the Tor website with https when you're not.</p>
<p>Some software sites list <a
href="http://en.wikipedia.org/wiki/Cryptographic_hash_function">sha1
hashes</a> alongside the software on their website, so users can
verify that they downloaded the file without any errors. These
"checksums" help you answer the question "Did I download this file
correctly from whoever sent it to me?" They do a good job at making
sure you didn't have any random errors in your download, but they
don't help you figure out whether you were downloading it from the
attacker. The better question to answer is: "Is this file that I
just downloaded the file that Tor intended me to get?"</p>
<h3>Where do I get the signatures and the keys that made them?</h3>
<hr>
<p>Each file on <a href="<page download/download>">our download
page</a> is accompanied by a file with the same name as the
package and the extension ".asc". These .asc files are GPG
signatures. They allow you to verify the file you've downloaded
is exactly the one that we intended you to get. For example,
tor-browser-<version-torbrowserbundle>_en-US.exe is accompanied by
tor-browser-<version-torbrowserbundle>_en-US.exe.asc. For a list
of which developer signs which package, see our <a href="<page
docs/signing-keys>">signing keys</a> page.</p>
<h3>Windows</h3>
<hr>
<p>You need to have GnuPG installed before
you can verify signatures. Download it from <a
href="http://gpg4win.org/download.html">http://gpg4win.org/download.html</a>.</p>
<p>Once it's installed, use GnuPG to import the key that signed your
package. Since GnuPG for Windows is a command-line tool, you will need
to use <i>cmd.exe</i>. Unless you edit your PATH environment variable,
you will need to tell Windows the full path to the GnuPG program. If
you installed GnuPG with the default values, the path should be
something like this: <i>C:\Program Files\Gnu\GnuPg\gpg.exe</i>.</p>
<p>Erinn Clark signs the Tor Browser Bundles. Import her key
(0x63FEE659) by starting <i>cmd.exe</i> and typing:</p>
<pre>C:\Program Files\Gnu\GnuPg\gpg.exe --keyserver x-hkp://pool.sks-keyservers.net --recv-keys 0x63FEE659</pre>
<p>After importing the key, you can verify that the fingerprint
is correct:</p>
<pre>C:\Program Files\Gnu\GnuPg\gpg.exe --fingerprint 0x63FEE659</pre>
<p>You should see:</p>
<pre>
pub 2048R/63FEE659 2003-10-16
Key fingerprint = 8738 A680 B84B 3031 A630 F2DB 416F 0610 63FE E659
uid Erinn Clark <erinn@torproject.org>
uid Erinn Clark <erinn@debian.org>
uid Erinn Clark <erinn@double-helix.org>
sub 2048R/EB399FD7 2003-10-16
</pre>
<p>To verify the signature of the package you downloaded, you will need
to download the ".asc" file as well. Assuming you downloaded the
package and its signature to your Desktop, run:</p>
<pre>C:\Program Files\Gnu\GnuPg\gpg.exe --verify C:\Users\Alice\Desktop\<file-win32-bundle-stable>.asc C:\Users\Alice\Desktop\<file-win32-bundle-stable></pre>
<p>The output should say "Good signature": </p>
<pre>
gpg: Signature made Wed 31 Aug 2011 06:37:01 PM EDT using RSA key ID 63FEE659
gpg: Good signature from "Erinn Clark <erinn@torproject.org>"
gpg: aka "Erinn Clark <erinn@debian.org>"
gpg: aka "Erinn Clark <erinn@double-helix.org>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: 8738 A680 B84B 3031 A630 F2DB 416F 0610 63FE E659
</pre>
<p>
Notice that there is a warning because you haven't assigned a trust
index to this person. This means that GnuPG verified that the key made
that signature, but it's up to you to decide if that key really belongs
to the developer. The best method is to meet the developer in person and
exchange key fingerprints.
</p>
<h3>Mac OS X</h3>
<hr>
<p>You need to have GnuPG installed before you can verify
signatures. You can install it from <a
href="http://www.gpgtools.org/">http://www.gpgtools.org/</a>.
</p>
<p>Once it's installed, use GnuPG to import the key that signed
your package. Erinn Clark signs the Tor Browser Bundles. Import her
key (0x63FEE659) by starting the terminal (under "Applications")
and typing:</p>
<pre>gpg --keyserver x-hkp://pool.sks-keyservers.net --recv-keys 0x63FEE659</pre>
<p>After importing the key, you can verify that the fingerprint
is correct:</p>
<pre>gpg --fingerprint 0x63FEE659</pre>
<p>You should see:</p>
<pre>
pub 2048R/63FEE659 2003-10-16
Key fingerprint = 8738 A680 B84B 3031 A630 F2DB 416F 0610 63FE E659
uid Erinn Clark <erinn@torproject.org>
uid Erinn Clark <erinn@debian.org>
uid Erinn Clark <erinn@double-helix.org>
sub 2048R/EB399FD7 2003-10-16
</pre>
<p>To verify the signature of the package you downloaded, you will need
to download the ".asc" file as well. Assuming you downloaded the
package and its signature to your Desktop, run:</p>
<pre>gpg --verify /Users/Alice/<file-osx-x86-bundle-stable>{.asc,}</pre>
<p>The output should say "Good signature": </p>
<pre>
gpg: Signature made Wed 31 Aug 2011 06:37:01 PM EDT using RSA key ID 63FEE659
gpg: Good signature from "Erinn Clark <erinn@torproject.org>"
gpg: aka "Erinn Clark <erinn@debian.org>"
gpg: aka "Erinn Clark <erinn@double-helix.org>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: 8738 A680 B84B 3031 A630 F2DB 416F 0610 63FE E659
</pre>
<p>
Notice that there is a warning because you haven't assigned a trust
index to this person. This means that GnuPG verified that the key made
that signature, but it's up to you to decide if that key really belongs
to the developer. The best method is to meet the developer in person and
exchange key fingerprints.
</p>
<h3>Linux</h3>
<hr>
<p>Most Linux distributions come with gpg preinstalled, so users
who want to verify the Tor Browser Bundle for Linux (or the source
tarball) can just follow along with the instructions above for
"Mac OS X". Note that sometimes Sebastian Hahn (key 0x140C961B)
signs the Linux TBB packages.</p>
<p>If you're using the <b>Debian</b> packages, you should read the
instructions on <a href="<page docs/debian>#packages">importing
these keys to apt</a>.</p>
<p>If you're using the <b>RPMs</b>, you can manually verify the
signatures on the RPM packages by <pre>rpm -K filename.rpm</pre></p>
<p>See <a
href="http://www.gnupg.org/documentation/">http://www.gnupg.org/documentation/</a>
to learn more about GPG.</p>
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