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284 lines
15 KiB
Plaintext
## translation metadata
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# Revision: $Revision$
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# Translation-Priority: 2-medium
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#include "head.wmi" TITLE="Tor Project: Verifying Signatures" CHARSET="UTF-8"
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<div id="content" class="clearfix">
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<div id="breadcrumbs">
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<a href="<page index>">Home » </a>
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<a href="<page docs/verifying-signatures>">Verifying Signatures</a>
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</div>
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<div id="maincol">
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<h1>How to verify signatures for packages</h1>
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<hr>
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<h3>What is a signature and why should I check it?</h3>
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<hr>
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<p>How do you know that the Tor program you have is really the
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one we made? Many Tor users have very real adversaries who might
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try to give them a fake version of Tor — and it doesn't matter
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how secure and anonymous Tor is if you're not running the real Tor.</p>
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<p>An attacker could try a variety of attacks to get you to download
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a fake Tor. For example, he could trick you into thinking some other
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website is a great place to download Tor. That's why you should
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always download Tor from <b>https</b>://www.torproject.org/. The
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https part means there's encryption and authentication between your
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browser and the website, making it much harder for the attacker
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to modify your download. But it's not perfect. Some places in the
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world block the Tor website, making users try <a href="<page
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docs/faq>#GetTor">somewhere else</a>. Large
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companies sometimes force employees to use a modified browser,
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so the company can listen in on all their browsing. We've even <a
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href="https://blog.torproject.org/blog/diginotar-debacle-and-what-you-should-do-about-it">seen</a>
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attackers who have the ability to trick your browser into thinking
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you're talking to the Tor website with https when you're not.</p>
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<p>Some software sites list <a
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href="https://en.wikipedia.org/wiki/Cryptographic_hash_function">sha1
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hashes</a> alongside the software on their website, so users can
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verify that they downloaded the file without any errors. These
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"checksums" help you answer the question "Did I download this file
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correctly from whoever sent it to me?" They do a good job at making
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sure you didn't have any random errors in your download, but they
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don't help you figure out whether you were downloading it from the
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attacker. The better question to answer is: "Is this file that I
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just downloaded the file that Tor intended me to get?"</p>
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<h3>Where do I get the signatures and the keys that made them?</h3>
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<hr>
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<p>Each file on <a href="<page download/download>">our download
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page</a> is accompanied by a file with the same name as the
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package and the extension ".asc". These .asc files are GPG
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signatures. They allow you to verify the file you've downloaded
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is exactly the one that we intended you to get. For example,
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torbrowser-install-<version-torbrowserbundle>_en-US.exe is accompanied by
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torbrowser-install-<version-torbrowserbundle>_en-US.exe.asc. For a list
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of which developer signs which package, see our <a href="<page docs/signing-keys>">signing keys</a> page.</p>
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<h3>Windows</h3>
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<hr>
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<p>You need to have GnuPG installed before
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you can verify signatures. Download it from <a
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href="https://gpg4win.org/download.html">https://gpg4win.org/download.html</a>.</p>
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<p>Once it's installed, use GnuPG to import the key that signed your
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package. Since GnuPG for Windows is a command-line tool, you will need
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to use <i>cmd.exe</i>. Unless you edit your PATH environment variable,
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you will need to tell Windows the full path to the GnuPG program. If
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you installed GnuPG with the default values, the path should be
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something like this: <i>C:\Program Files\Gnu\GnuPg\gpg.exe</i>.</p>
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<p>The Tor Browser team signs Tor Browser releases. Import its key
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(0x4E2C6E8793298290) by starting <i>cmd.exe</i> and typing:</p>
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<pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290</pre>
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<p>After importing the key, you can verify that the fingerprint
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is correct:</p>
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<pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --fingerprint 0x4E2C6E8793298290</pre>
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<p>You should see:</p>
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<pre>
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pub 4096R/93298290 2014-12-15
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Key fingerprint = EF6E 286D DA85 EA2A 4BA7 DE68 4E2C 6E87 9329 8290
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uid Tor Browser Developers (signing key) <torbrowser@torproject.org>
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sub 4096R/F65C2036 2014-12-15
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sub 4096R/D40814E0 2014-12-15
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sub 4096R/C3C07136 2016-08-24
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</pre>
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<p>To verify the signature of the package you downloaded, you will need
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to download the ".asc" file as well. Assuming you downloaded the
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package and its signature to your Desktop, run:</p>
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<pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --verify C:\Users\Alice\Desktop\torbrowser-install-<version-torbrowserbundle>_en-US.exe.asc C:\Users\Alice\Desktop\torbrowser-install-<version-torbrowserbundle>_en-US.exe</pre>
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<p>The output should say "Good signature": </p>
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<pre>
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gpg: Signature made Tue 24 Jan 2015 09:29:09 AM CET using RSA key ID D40814E0
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gpg: Good signature from "Tor Browser Developers (signing key) <torbrowser@torproject.org>"
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7 DE68 4E2C 6E87 9329 8290</pre>
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<p>Currently valid subkey fingerprints are:
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<pre>
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5242 013F 02AF C851 B1C7 36B8 7017 ADCE F65C 2036
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BA1E E421 BBB4 5263 180E 1FC7 2E1A C68E D408 14E0
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A430 0A6B C93C 0877 A445 1486 D148 3FA6 C3C0 7136</pre></p>
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<p>
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Notice that there is a warning because you haven't assigned a trust
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index to this person. This means that GnuPG verified that the key made
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that signature, but it's up to you to decide if that key really belongs
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to the developer. The best method is to meet the developer in person and
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exchange key fingerprints.
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</p>
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<h3>Mac OS X and Linux</h3>
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<hr>
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<p>You need to have GnuPG installed before you can verify
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signatures. If you are using Mac OS X, you can install it from <a
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href="https://www.gpgtools.org/">https://www.gpgtools.org/</a>. If you
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are using Linux, then it's probably you already have GnuPG in your
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system, as most Linux distributions come with it preinstalled.
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</p>
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<p>The next step is to use GnuPG to import the key that signed
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your package. The Tor Browser team signs Tor Browser releases. Import its
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key (0x4E2C6E8793298290) by starting the terminal (under "Applications"
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in Mac OS X) and typing:</p>
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<pre>gpg --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290</pre>
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<p>After importing the key, you can verify that the fingerprint
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is correct:</p>
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<pre>gpg --fingerprint 0x4E2C6E8793298290</pre>
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<p>You should see:</p>
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<pre>
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pub 4096R/93298290 2014-12-15
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Key fingerprint = EF6E 286D DA85 EA2A 4BA7 DE68 4E2C 6E87 9329 8290
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uid Tor Browser Developers (signing key) <torbrowser@torproject.org>
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sub 4096R/F65C2036 2014-12-15
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sub 4096R/D40814E0 2014-12-15
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sub 4096R/C3C07136 2016-08-24</pre>
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<p>To verify the signature of the package you downloaded, you will need
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to download the ".asc" file as well. Assuming you downloaded the
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package and its signature to your Downloads folder, run:</p>
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<strong>For Mac OS X users</strong>:<br />
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<pre>gpg --verify ~/Downloads/TorBrowser-<version-torbrowserbundleosx64>-osx64_en-US.dmg{.asc*,}</pre>
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<strong>For Linux users</strong> (change 32 to 64 if you have the 64-bit package):<br />
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<pre>gpg --verify ~/Desktop/tor-browser-linux32-<version-torbrowserbundlelinux32>_en-US.tar.xz{.asc*,}</pre>
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<p>The output should say "Good signature":</p>
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<pre>
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gpg: Signature made Tue 24 Jan 2015 09:29:09 AM CET using RSA key ID D40814E0
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gpg: Good signature from "Tor Browser Developers (signing key) <torbrowser@torproject.org>"
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7 DE68 4E2C 6E87 9329 8290</pre> <p> Currently valid subkey fingerprints are:
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<pre>
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5242 013F 02AF C851 B1C7 36B8 7017 ADCE F65C 2036
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BA1E E421 BBB4 5263 180E 1FC7 2E1A C68E D408 14E0
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A430 0A6B C93C 0877 A445 1486 D148 3FA6 C3C0 7136</pre></p>
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<p>
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Notice that there is a warning because you haven't assigned a trust
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index to this person. This means that GnuPG verified that the key made
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that signature, but it's up to you to decide if that key really belongs
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to the developer. The best method is to meet the developer in person and
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exchange key fingerprints.
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</p>
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<p>
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If you're a Linux user and you're using the <b>Debian</b> Tor (not Tor
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Browser) packages, you should read the instructions on <a
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href="<page docs/debian>#packages">importing these keys to apt</a>.
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If you're using the <b>RPMs</b> (for Tor, not Tor Browser), you can
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manually verify the signatures on the RPM packages by
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<pre>rpm -K filename.rpm</pre>
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</p>
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<p>See <a
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href="https://www.gnupg.org/documentation/">https://www.gnupg.org/documentation/</a>
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to learn more about GnuPG.</p>
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<hr>
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<a id="BuildVerification"></a>
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<h3><a class="anchor" href="#BuildVerification">
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Verifying sha256sums (advanced)</a></h3>
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<hr>
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<p>Build reproducibility is a <a
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href="https://blog.torproject.org/blog/deterministic-builds-part-one-cyberwar-and-global-compromise">security
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property</a> of Tor Browser 3.0 and later. Anyone can build
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Tor Browser on their own machine and produce a binary that is
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bit-for-bit identical to the binary we offer on the download page.
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Fortunately, it is not necessary for everyone to build Tor Browser
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locally to get this security. Verifying and comparing the signed list
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of <a href="https://en.wikipedia.org/wiki/Cryptographic_hash">hashes</a>
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will confirm that multiple people have built Tor Browsers
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identical to the download.</p>
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<p>The steps below walk through this process:</p>
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<ul>
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<li>Download the Tor Browser package, the <tt>sha256sums-unsigned-build.txt</tt>
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file, and the <tt>sha256sums-unsigned-build.txt.asc</tt> signature file.
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They can all be found in the same directory under
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<a href="https://www.torproject.org/dist/torbrowser/">
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https://www.torproject.org/dist/torbrowser/</a>, for example in '<version-torbrowserbundlelinux32>'
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for Tor Browser <version-torbrowserbundlelinux32>.</li>
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<li>In case your operating system is adding the .txt extension
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automatically to the SHA256 sums signature file strip it again by running
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<pre>mv sha256sums-unsigned-build.txt.asc.txt sha256sums-unsigned-build.txt.asc</pre>
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<li>Retrieve the signers' GPG keys. This can be done from the command
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line by entering something like
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<pre>gpg --keyserver keys.mozilla.org --recv-keys 0x4E2C6E8793298290</pre>
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(This will bring you the public part of the Tor Browser developers'
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signing key. Other developers' key IDs can be found on
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<a href="<page docs/signing-keys>">this
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page</a>.)</li>
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<li>Verify the sha256sums-unsigned-build.txt file by executing this
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command:
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<pre>gpg --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt</pre></li>
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<li>You should see a message like "Good signature from <DEVELOPER
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NAME>". If you don't, there is a problem. Try these steps again.</li>
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<li>If you want to verify a Windows Tor Browser package you need to first
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strip off the authenticode signature of it. Tools that can be used for
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this purpose are <a href="http://osslsigncode.sourceforge.net">osslsigncode</a> and
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<a href="http://forum.xda-developers.com/showthread.php?t=416175">delcert.exe</a>.
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Assuming you have built e.g. <tt>osslsigncode</tt> on a Linux computer you can enter
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<pre>/path/to/your/osslsigncode remove-signature \
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/path/to/your/<TOR BROWSER FILE NAME>.exe <TOR BROWSER FILE NAME>.exe</pre></li>
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<li>Now you can take the sha256sum of the Tor Browser package. On
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Windows you can use the <a href="http://md5deep.sourceforge.net/">
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hashdeep utility</a> and run
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<pre>C:\location\where\you\saved\hashdeep -c sha256sum <TOR BROWSER FILE NAME>.exe</pre>
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On Mac or Linux you can run <pre>shasum -a 256 <TOR BROWSER FILE NAME>.dmg</pre> or <pre>sha256sum <TOR BROWSER FILE NAME>.tar.gz</pre> without having to download a utility.</li>
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<li>You will see a string of letters and numbers.</li>
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<li>Open <tt>sha256sums-unsigned-build.txt</tt> in a text editor.</li>
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<li>Locate the name of the Tor Browser file you downloaded.</li>
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<li>Compare the string of letters and numbers to the left of your
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filename with the string of letters and numbers that appeared
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on your command line. If they match, you've successfully verified the
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build.</li>
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</ul>
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<p><a href="https://github.com/isislovecruft/scripts/blob/master/verify-gitian-builder-signatures">Scripts</a>
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to <a href="https://tor.stackexchange.com/questions/648/how-to-verify-tor-browser-bundle-tbb-3-x">automate</a>
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these steps have been written, but to use them you will need to modify
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them yourself with the latest Tor Browser filename.</p>
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<hr>
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<a id="MARVerification"></a>
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<h3><a class="anchor" href="#MARVerification">
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Verifying MAR files we ship (advanced)</a></h3>
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<hr>
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<p>Starting with Tor Browser 4.5a4 we sign our MAR files which helps
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securing our update process. The downside of this is the need for additional
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instructions to verify that the MAR files we ship are indeed the ones we
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produced with our Gitian setup.</p>
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<p>Assuming the verification happens on a Linux computer one first needs the
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<tt>mar-tools-linux*.zip</tt> out of the <tt>gitian-builder/inputs</tt>
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directory to remove the embedded signature(s). The steps to get the unsigned
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MAR file on a 64 bit Linux are</p>
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<pre>
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cd /path/to/MAR/file
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unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip
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export LD_LIBRARY_PATH=/path/to/MAR/file/mar-tools
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mar-tools/signmar -r your-signed-mar-file.mar your-unsigned-mar-file.mar</pre>
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<p>Now you can compare the SHA256 sum of <tt>your-unsigned-mar-file.mar</tt>
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with the one provided in the <tt>sha265sums-unsigned-build.txt</tt> or
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<tt>sha256sums-unsigned-build.incremental.txt</tt> as outlined in
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<a href="#BuildVerification">Verifying sha256sums (advancded)</a> above.</p>
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</div>
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<!-- END MAINCOL -->
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<div id = "sidecol">
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#include "side.wmi"
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#include "info.wmi"
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</div>
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<!-- END SIDECOL -->
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</div>
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<!-- END CONTENT -->
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#include <foot.wmi>
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