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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)     torbrowser-install-<version-torbrowserbundle>_en-US.exe is accompanied by
57)     torbrowser-install-<version-torbrowserbundle>_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>The Tor Browser team signs the Tor Browsers. Import its key
71)     (0x4E2C6E8793298290) 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 0x4E2C6E8793298290</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 0x4E2C6E8793298290</pre>

76)     <p>You should see:</p>
77)     <pre>

78)     pub   4096R/93298290 2014-12-15
79)           Key fingerprint = EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
80)     uid                  Tor Browser Developers (signing key) <torbrowser@torproject.org>
81)     sub   4096R/F65C2036 2014-12-15
82)     sub   4096R/D40814E0 2014-12-15
83)     sub   4096R/589839A3 2014-12-15

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\torbrowser-install-<version-torbrowserbundle>_en-US.exe.asc C:\Users\Alice\Desktop\torbrowser-install-<version-torbrowserbundle>_en-US.exe</pre>

89)     <p>The output should say "Good signature": </p>
90)     <pre>

91)     gpg: Signature made Tue 24 Jan 2015 09:29:09 AM CET using RSA key ID D40814E0
92)     gpg: Good signature from "Tor Browser Developers (signing key) <torbrowser@torproject.org>"

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

95)     Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290

96)     </pre>
97)     <p>
98)     Notice that there is a warning because you haven't assigned a trust
99)     index to this person. This means that GnuPG verified that the key made
100)     that signature, but it's up to you to decide if that key really belongs
101)     to the developer. The best method is to meet the developer in person and
102)     exchange key fingerprints.
103)     </p>

104)     <h3>Mac OS X and Linux</h3>

105)     <hr>

106) 

107)     <p>You need to have GnuPG installed before you can verify

108)     signatures. If you are using Mac OS X, you can install it from <a
109)     href="http://www.gpgtools.org/">http://www.gpgtools.org/</a>. If you
110)     are using Linux, then it's probably you already have GnuPG in your
111)     system, as most Linux distributions come with it preinstalled.

112)     </p>

113) 

114)     <p>The next step is to use GnuPG to import the key that signed

115)     your package. The Tor Browser team signs the Tor Browsers. Import its
116)     key (0x4E2C6E8793298290) by starting the terminal (under "Applications"

117)     in Mac OS X) and typing:</p>

118) 

119)     <pre>gpg --keyserver x-hkp://pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290</pre>

120) 

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

124)     <pre>gpg --fingerprint 0x4E2C6E8793298290</pre>

125) 

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

128)     pub   4096R/93298290 2014-12-15
129)           Key fingerprint = EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
130)     uid                  Tor Browser Developers (signing key) <torbrowser@torproject.org>
131)     sub   4096R/F65C2036 2014-12-15
132)     sub   4096R/D40814E0 2014-12-15
133)     sub   4096R/589839A3 2014-12-15

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)     <strong>For Mac OS X users</strong>:<br />
141)     <pre>gpg --verify ~/Desktop/TorBrowser-<version-torbrowserbundleosx32>-osx32_en-US.dmg{.asc*,}</pre>

142)     

143)     <strong>For Linux users</strong> (change 32 to 64 if you have the 64-bit package):<br />

144)     <pre>gpg --verify ~/Desktop/tor-browser-linux32-<version-torbrowserbundlelinux32>_en-US.tar.xz{.asc*,}</pre>

145) 

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

147) 

148)     <pre>

149)     gpg: Signature made Tue 24 Jan 2015 09:29:09 AM CET using RSA key ID D40814E0
150)     gpg: Good signature from "Tor Browser Developers (signing key) <torbrowser@torproject.org>"

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

153)     Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290

154)     </pre>

155) 

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

163)     
164)     <p>
165)     If you're a Linux user and you're using the <b>Debian</b> Tor (not Tor
166)     Browser) packages, you should read the instructions on <a
167)     href="<page docs/debian>#packages">importing these keys to apt</a>.
168)     If you're using the <b>RPMs</b> (for Tor, not Tor Browser), you can
169)     manually verify the signatures on the RPM packages by
170)     <pre>rpm -K filename.rpm</pre>
171)     </p>

172) 
173)     <p>See <a
174)     href="http://www.gnupg.org/documentation/">http://www.gnupg.org/documentation/</a>

175)     to learn more about GnuPG.</p>
176) 
177)     <hr>

178) 

179)     <a id="BuildVerification"></a>
180)     <h3><a class="anchor" href="#BuildVerification">
181)     Verifying sha256sums (advanced)</a></h3>
182)     <hr>

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

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

192)        identical to the download.</p>
193) 
194)       <p>The steps below walk through this process:</p>
195) 
196)     <ul>
197)       <li>Download the Tor Browser package, the sha256sums.txt file, and the

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

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

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

201)       for TBB 3.6.1.</li>

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

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

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

206)       developers' key IDs can be found on

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

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

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

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

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

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

217)       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>

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

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

225)     </ul>

226) 
227)     <p><a href="https://github.com/isislovecruft/scripts/blob/master/verify-gitian-builder-signatures">Scripts</a>
228)     to <a href="http://tor.stackexchange.com/questions/648/how-to-verify-tor-browser-bundle-tbb-3-x">automate</a>
229)     these steps have been written, but to use them you will need to modify

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

231) 
232)     <hr>
233) 
234)     <a id="MARVerification"></a>
235)     <h3><a class="anchor" href="#MARVerification">
236)     Verifying MAR files we ship (advanced)</a></h3>

237)     <hr>

238)     <p>Starting with Tor Browser 4.5a4 we sign our MAR files which helps
239)     securing our update process. The downside of this is the need for additional
240)     instructions to verify that the MAR files we ship are indeed the ones we
241)     produced with our Gitian setup.</p>
242) 
243)     <p>Assuming the verification happens on a Linux computer one first needs the
244)     <tt>mar-tools-linux*.zip</tt> out of the <tt>gitian-builder/inputs</tt>
245)     directory to remove the embedded signature(s). The steps to get the unsigned
246)     MAR file on a 64 bit Linux are</p>
247)     <pre>
248)     cd /path/to/MAR/file
249)     unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip
250)     mar-tools/signmar -r your-signed-mar-file.mar your-unsigned-mar-file.mar</pre>
251)     <p>Now you can compare the SHA256 sum of <tt>your-unsigned-mar-file.mar</tt>
252)     with the one provided in the <tt>sha265sums.txt</tt> or
253)     <tt>sha256sums.incremental.txt</tt> as outlined in <a href="#BuildVerification">Verifying
254)     sha256sums (advancded)</a> above.</p>

255) 

256)   </div>
257)   <!-- END MAINCOL -->
258)   <div id = "sidecol">
259) #include "side.wmi"
260) #include "info.wmi"
261)   </div>
262)   <!-- END SIDECOL -->
263) </div>
264) <!-- END CONTENT -->