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5) #include "head.wmi" TITLE="Tor Project: Verifying Signatures" CHARSET="UTF-8"
6) <div id="content" class="clearfix">
7)   <div id="breadcrumbs">

8)     <a href="<page index>">Home &raquo; </a>

9)     <a href="<page docs/verifying-signatures>">Verifying Signatures</a>
10)   </div>

11)   <div id="maincol">

12)     <h1>How to verify signatures for packages</h1>

13)     <hr>

14) 

15)     <h3>What is a signature and why should I check it?</h3>
16)     <hr>
17) 
18)     <p>How do you know that the Tor program you have is really the
19)     one we made? Many Tor users have very real adversaries who might
20)     try to give them a fake version of Tor &mdash; and it doesn't matter
21)     how secure and anonymous Tor is if you're not running the real Tor.</p>
22) 
23)     <p>An attacker could try a variety of attacks to get you to download
24)     a fake Tor. For example, he could trick you into thinking some other
25)     website is a great place to download Tor. That's why you should
26)     always download Tor from <b>https</b>://www.torproject.org/. The
27)     https part means there's encryption and authentication between your
28)     browser and the website, making it much harder for the attacker
29)     to modify your download. But it's not perfect. Some places in the

30)     world block the Tor website, making users try <a href="<page
31)     docs/faq>#GetTor">somewhere else</a>. Large

32)     companies sometimes force employees to use a modified browser,
33)     so the company can listen in on all their browsing. We've even <a
34)     href="https://blog.torproject.org/blog/diginotar-debacle-and-what-you-should-do-about-it">seen</a>
35)     attackers who have the ability to trick your browser into thinking
36)     you're talking to the Tor website with https when you're not.</p>
37) 
38)     <p>Some software sites list <a
39)     href="http://en.wikipedia.org/wiki/Cryptographic_hash_function">sha1
40)     hashes</a> alongside the software on their website, so users can
41)     verify that they downloaded the file without any errors. These
42)     "checksums" help you answer the question "Did I download this file
43)     correctly from whoever sent it to me?" They do a good job at making
44)     sure you didn't have any random errors in your download, but they
45)     don't help you figure out whether you were downloading it from the
46)     attacker. The better question to answer is: "Is this file that I
47)     just downloaded the file that Tor intended me to get?"</p>
48) 

49)     <h3>Where do I get the signatures and the keys that made them?</h3>
50)     <hr>

51)     <p>Each file on <a href="<page download/download>">our download

52)     page</a> is accompanied by a file with the same name as the
53)     package and the extension ".asc". These .asc files are GPG
54)     signatures. They allow you to verify the file you've downloaded
55)     is exactly the one that we intended you to get. For example,

56)     tor-browser-2.3.25-13_en-US.exe is accompanied by
57)     tor-browser-2.3.25-13_en-US.exe.asc. For a list

58)     of which developer signs which package, see our <a href="<page docs/signing-keys>">signing keys</a> page.</p>

59)     <h3>Windows</h3>

60)     <hr>

61)     <p>You need to have GnuPG installed before
62)     you can verify signatures. Download it from <a

63)     href="http://gpg4win.org/download.html">http://gpg4win.org/download.html</a>.</p>

64)     <p>Once it's installed, use GnuPG to import the key that signed your
65)     package. Since GnuPG for Windows is a command-line tool, you will need

66)     to use <i>cmd.exe</i>. Unless you edit your PATH environment variable,
67)     you will need to tell Windows the full path to the GnuPG program. If
68)     you installed GnuPG with the default values, the path should be
69)     something like this: <i>C:\Program Files\Gnu\GnuPg\gpg.exe</i>.</p>

70)     <p>Erinn Clark signs the Tor Browsers. Import her key

71)     (0x416F061063FEE659) by starting <i>cmd.exe</i> and typing:</p>
72)     <pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --keyserver x-hkp://pool.sks-keyservers.net --recv-keys 0x416F061063FEE659</pre>
73)     <p>After importing the key, you can verify that the fingerprint

74)     is correct:</p>

75)     <pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --fingerprint 0x416F061063FEE659</pre>

76)     <p>You should see:</p>
77)     <pre>
78)     pub   2048R/63FEE659 2003-10-16
79)           Key fingerprint = 8738 A680 B84B 3031 A630  F2DB 416F 0610 63FE E659
80)     uid                  Erinn Clark &lt;erinn@torproject.org&gt;
81)     uid                  Erinn Clark &lt;erinn@debian.org&gt;
82)     uid                  Erinn Clark &lt;erinn@double-helix.org&gt;
83)     sub   2048R/EB399FD7 2003-10-16
84) </pre>
85)     <p>To verify the signature of the package you downloaded, you will need
86)     to download the ".asc" file as well. Assuming you downloaded the
87)     package and its signature to your Desktop, run:</p>

88)     <pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --verify C:\Users\Alice\Desktop\tor-browser-2.3.25-13_en-US.exe.asc C:\Users\Alice\Desktop\tor-browser-2.3.25-13_en-US.exe</pre>

89)     <p>The output should say "Good signature": </p>
90)     <pre>
91)     gpg: Signature made Wed 31 Aug 2011 06:37:01 PM EDT using RSA key ID 63FEE659
92)     gpg: Good signature from "Erinn Clark &lt;erinn@torproject.org&gt;"
93)     gpg:                 aka "Erinn Clark &lt;erinn@debian.org&gt;"
94)     gpg:                 aka "Erinn Clark &lt;erinn@double-helix.org&gt;"
95)     gpg: WARNING: This key is not certified with a trusted signature!
96)     gpg:          There is no indication that the signature belongs to the owner.
97)     Primary key fingerprint: 8738 A680 B84B 3031 A630  F2DB 416F 0610 63FE E659
98)     </pre>
99)     <p>
100)     Notice that there is a warning because you haven't assigned a trust
101)     index to this person. This means that GnuPG verified that the key made
102)     that signature, but it's up to you to decide if that key really belongs
103)     to the developer. The best method is to meet the developer in person and
104)     exchange key fingerprints.
105)     </p>
106)     <h3>Mac OS X</h3>

107)     <hr>

108) 

109)     <p>You need to have GnuPG installed before you can verify
110)     signatures. You can install it from <a

111)     href="http://www.gpgtools.org/">http://www.gpgtools.org/</a>.

112)     </p>

113) 

114)     <p>Once it's installed, use GnuPG to import the key that signed

115)     your package. Erinn Clark signs the Tor Browsers. Import her

116)     key (0x416F061063FEE659) by starting the terminal (under "Applications")

117)     and typing:</p>

118) 

119)     <pre>gpg --keyserver x-hkp://pool.sks-keyservers.net --recv-keys 0x416F061063FEE659</pre>

120) 

121)     <p>After importing the key, you can verify that the fingerprint
122)     is correct:</p>
123) 

124)     <pre>gpg --fingerprint 0x416F061063FEE659</pre>

125) 

126)     <p>You should see:</p>
127)     <pre>

128)     pub   2048R/63FEE659 2003-10-16
129)           Key fingerprint = 8738 A680 B84B 3031 A630  F2DB 416F 0610 63FE E659
130)     uid                  Erinn Clark <erinn@torproject.org>
131)     uid                  Erinn Clark <erinn@debian.org>
132)     uid                  Erinn Clark <erinn@double-helix.org>
133)     sub   2048R/EB399FD7 2003-10-16
134)     </pre>

135) 

136)     <p>To verify the signature of the package you downloaded, you will need
137)     to download the ".asc" file as well. Assuming you downloaded the
138)     package and its signature to your Desktop, run:</p>

139) 

140)     <pre>gpg --verify ~/Desktop/TorBrowser-<version-torbrowserbundleosx32>-osx32_en-US.dmg{.asc*,}</pre>

141) 

142)     <p>The output should say "Good signature": </p>

143) 

144)     <pre>

145)     gpg: Signature made Wed 31 Aug 2011 06:37:01 PM EDT using RSA key ID 63FEE659
146)     gpg: Good signature from "Erinn Clark <erinn@torproject.org>"
147)     gpg:                 aka "Erinn Clark <erinn@debian.org>"
148)     gpg:                 aka "Erinn Clark <erinn@double-helix.org>"

149)     gpg: WARNING: This key is not certified with a trusted signature!
150)     gpg:          There is no indication that the signature belongs to the owner.

151)     Primary key fingerprint: 8738 A680 B84B 3031 A630  F2DB 416F 0610 63FE E659

152)     </pre>

153) 

154)     <p>
155)     Notice that there is a warning because you haven't assigned a trust
156)     index to this person. This means that GnuPG verified that the key made
157)     that signature, but it's up to you to decide if that key really belongs
158)     to the developer. The best method is to meet the developer in person and
159)     exchange key fingerprints.
160)     </p>

161) 

162)     <h3>Linux</h3>
163)     <hr>

164) 

165)     <p>Most Linux distributions come with gpg preinstalled, so users

166)     who want to verify the Tor Browser for Linux (or the source

167)     tarball) can just follow along with the instructions above for

168)     "Mac OS X". </p>

169) 

170)     <p>If you're using the <b>Debian</b> Tor (not Tor Browser) packages, you 
171)     should read the

172)     instructions on <a href="<page docs/debian>#packages">importing
173)     these keys to apt</a>.</p>

174) 

175)     <p>If you're using the <b>RPMs</b> (for Tor, not Tor Browser), you can 
176)     manually verify the

177)     signatures on the RPM packages by <pre>rpm -K filename.rpm</pre></p>
178) 
179)     <p>See <a
180)     href="http://www.gnupg.org/documentation/">http://www.gnupg.org/documentation/</a>
181)     to learn more about GPG.</p>

182) 

183)     <hr>
184) 
185)     <a id="BuildVerification"></a>
186)     <h3><a class="anchor" href="#BuildVerification">
187)     Verifying sha256sums (advanced)</a></h3>
188)     <hr>

189)     <p>Build reproducibility is a <a
190)        href="https://blog.torproject.org/blog/deterministic-builds-part-one-cyberwar-and-global-compromise">security

191)        property</a> of Tor Browser 3.0 and later. Anyone can build
192)        Tor Browser on their own machine and produce a binary that is
193)        bit-for-bit identical to the binary we offer on the download page.
194)        Fortunately, it is not necessary for everyone to build the Tor Browser
195)        locally to get this security. Verifying and comparing the signed list
196)        of <a href="https://en.wikipedia.org/wiki/Cryptographic_hash">hashes</a>
197)        will confirm that multiple people have built Tor Browsers

198)        identical to the download.</p>
199) 
200)       <p>The steps below walk through this process:</p>
201) 
202)     <ul>
203)       <li>Download the Tor Browser package, the sha256sums.txt file, and the

204)       sha256sums signature files. They can all be found in the same directory

205)       under <a href="https://www.torproject.org/dist/torbrowser/">

206)       https://www.torproject.org/dist/torbrowser/</a>, for example in '3.6.1'

207)       for TBB 3.6.1.</li>

208)       <li>Retrieve the signers' GPG keys. This can be done from the command
209)       line by entering something like

210)       <pre>gpg --keyserver keys.mozilla.org --recv-keys 0x29846B3C683686CC</pre>

211)       (This will bring you developer Mike Perry's public key. Other

212)       developers' key IDs can be found on

213)       <a href="<page docs/signing-keys>">this

214)       page</a>.)</li>
215)       <li>Verify the sha256sums.txt file by executing this command:
216)       <pre>gpg --verify &lt;NAME OF THE SIGNATURE FILE&gt;.asc sha256sums.txt</pre></li>

217)       <li>You should see a message like "Good signature from &lt;DEVELOPER

218)       NAME&gt;". If you don't, there is a problem. Try these steps again.</li>

219)       <li>Now you can take the sha256sum of the Tor Browser package. On

220)       Windows you can use the <a href="http://md5deep.sourceforge.net/">
221)       hashdeep utility</a> and run
222)       <pre>C:\location\where\you\saved\hashdeep -c sha256sum &lt;TOR BROWSER FILE NAME&gt;.exe</pre>

223)       On Mac or Linux you can run <pre>sha256sum &lt;TOR BROWSER FILE NAME&gt;.dmg</pre> or <pre>sha256sum &lt;TOR BROWSER FILE NAME&gt;.tar.gz</pre> without having to download a utility.</li>

224)       <li>You will see a string of letters and numbers.</li>
225)       <li>Open sha256sums.txt in a text editor.</li>
226)       <li>Locate the name of the Tor Browser file you downloaded.</li>
227)       <li>Compare the string of letters and numbers to the left of your

228)       filename with the string of letters and numbers that appeared
229)       on your command line. If they match, you've successfully verified the
230)       build.</li>

231)     </ul>

232) 
233)     <p><a href="https://github.com/isislovecruft/scripts/blob/master/verify-gitian-builder-signatures">Scripts</a>
234)     to <a href="http://tor.stackexchange.com/questions/648/how-to-verify-tor-browser-bundle-tbb-3-x">automate</a>
235)     these steps have been written, but to use them you will need to modify

236)     them yourself with the latest Tor Browser filename.</p>

237) 
238)     <hr>
239) 
240)     <a id="MARVerification"></a>
241)     <h3><a class="anchor" href="#MARVerification">
242)     Verifying MAR files we ship (advanced)</a></h3>

243)     <hr>

244)     <p>Starting with Tor Browser 4.5a4 we sign our MAR files which helps
245)     securing our update process. The downside of this is the need for additional
246)     instructions to verify that the MAR files we ship are indeed the ones we
247)     produced with our Gitian setup.</p>
248) 
249)     <p>Assuming the verification happens on a Linux computer one first needs the
250)     <tt>mar-tools-linux*.zip</tt> out of the <tt>gitian-builder/inputs</tt>
251)     directory to remove the embedded signature(s). The steps to get the unsigned
252)     MAR file on a 64 bit Linux are</p>
253)     <pre>
254)     cd /path/to/MAR/file
255)     unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip
256)     mar-tools/signmar -r your-signed-mar-file.mar your-unsigned-mar-file.mar</pre>
257)     <p>Now you can compare the SHA256 sum of <tt>your-unsigned-mar-file.mar</tt>
258)     with the one provided in the <tt>sha265sums.txt</tt> or
259)     <tt>sha256sums.incremental.txt</tt> as outlined in <a href="#BuildVerification">Verifying
260)     sha256sums (advancded)</a> above.</p>

261) 

262)   </div>
263)   <!-- END MAINCOL -->
264)   <div id = "sidecol">
265) #include "side.wmi"
266) #include "info.wmi"
267)   </div>
268)   <!-- END SIDECOL -->
269) </div>
270) <!-- END CONTENT -->