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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="https://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="https://gpg4win.org/download.html">https://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 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/C3C07136 2016-08-24

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</pre>
96)     <p>Currently valid subkey fingerprints are:
97)     <pre>
98)     5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036

99)     BA1E E421 BBB4 5263 180E  1FC7 2E1A C68E D408 14E0
100)     A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136</pre></p>

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

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

109)     <hr>

110) 

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

112)     signatures. If you are using Mac OS X, you can install it from <a

113)     href="https://www.gpgtools.org/">https://www.gpgtools.org/</a>. If you

114)     are using Linux, then it's probably you already have GnuPG in your
115)     system, as most Linux distributions come with it preinstalled.

116)     </p>

117) 

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

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

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

122) 

123)     <pre>gpg --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290</pre>

124) 

125)     <p>After importing the key, you can verify that the fingerprint
126)     is correct:</p>
127) 

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

129) 

130)     <p>You should see:</p>
131)     <pre>

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

136)     sub   4096R/D40814E0 2014-12-15
137)     sub   4096R/C3C07136 2016-08-24</pre>

138)     <p>To verify the signature of the package you downloaded, you will need
139)     to download the ".asc" file as well. Assuming you downloaded the

140)     package and its signature to your Downloads folder, run:</p>

141) 

142)     <strong>For Mac OS X users</strong>:<br />

143)     <pre>gpg --verify ~/Downloads/TorBrowser-<version-torbrowserbundleosx64>-osx64_en-US.dmg{.asc*,}</pre>
144) 

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

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

147) 

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

149) 

150)     <pre>

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

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

155)     Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290</pre> <p> Currently valid subkey fingerprints are:
156)     <pre>
157)     5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036

158)     BA1E E421 BBB4 5263 180E  1FC7 2E1A C68E D408 14E0
159)     A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136</pre></p>

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

167) 

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

176) 
177)     <p>See <a

178)     href="https://www.gnupg.org/documentation/">https://www.gnupg.org/documentation/</a>

179)     to learn more about GnuPG.</p>
180) 
181)     <hr>

182) 

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

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

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

196)        identical to the download.</p>
197) 
198)       <p>The steps below walk through this process:</p>
199) 
200)     <ul>

201)       <li>Download the Tor Browser package, the <tt>sha256sums-unsigned-build.txt</tt>
202)       file, and the <tt>sha256sums-unsigned-build.txt.asc</tt> signature file.
203)       They can all be found in the same directory under
204)       <a href="https://www.torproject.org/dist/torbrowser/">

205)       https://www.torproject.org/dist/torbrowser/</a>, for example in '<version-torbrowserbundlelinux32>'
206)       for Tor Browser <version-torbrowserbundlelinux32>.</li>
207)       <li>In case your operating system is adding the .txt extension
208)       automatically to the SHA256 sums signature file strip it again by running
209)       <pre>mv sha256sums-unsigned-build.txt.asc.txt sha256sums-unsigned-build.txt.asc</pre>

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

212)       <pre>gpg --keyserver keys.mozilla.org --recv-keys 0x4E2C6E8793298290</pre>
213)       (This will bring you the public part of the Tor Browser developers'

214)        signing key. Other developers' key IDs can be found on

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

216)       page</a>.)</li>

217)       <li>Verify the sha256sums-unsigned-build.txt file by executing this
218)       command:
219)       <pre>gpg --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt</pre></li>

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

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

222)       <li>If you want to verify a Windows Tor Browser package you need to first

223)       strip off the authenticode signature of it. Tools that can be used for
224)       this purpose are <a href="http://osslsigncode.sourceforge.net">osslsigncode</a> and
225)       <a href="http://forum.xda-developers.com/showthread.php?t=416175">delcert.exe</a>.
226)       Assuming you have built e.g. <tt>osslsigncode</tt> on a Linux computer you can enter

227)       <pre>/path/to/your/osslsigncode remove-signature &#92;
228)         /path/to/your/&lt;TOR BROWSER FILE NAME&gt;.exe &lt;TOR BROWSER FILE NAME&gt;.exe</pre></li>

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

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

233)       On Mac or Linux you can run <pre>shasum -a 256 &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>

234)       <li>You will see a string of letters and numbers.</li>

235)       <li>Open <tt>sha256sums-unsigned-build.txt</tt> in a text editor.</li>

236)       <li>Locate the name of the Tor Browser file you downloaded.</li>
237)       <li>Compare the string of letters and numbers to the left of your

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

241)     </ul>

242) 
243)     <p><a href="https://github.com/isislovecruft/scripts/blob/master/verify-gitian-builder-signatures">Scripts</a>

244)     to <a href="https://tor.stackexchange.com/questions/648/how-to-verify-tor-browser-bundle-tbb-3-x">automate</a>

245)     these steps have been written, but to use them you will need to modify

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

247) 
248)     <hr>
249) 
250)     <a id="MARVerification"></a>
251)     <h3><a class="anchor" href="#MARVerification">
252)     Verifying MAR files we ship (advanced)</a></h3>

253)     <hr>

254)     <p>Starting with Tor Browser 4.5a4 we sign our MAR files which helps
255)     securing our update process. The downside of this is the need for additional
256)     instructions to verify that the MAR files we ship are indeed the ones we
257)     produced with our Gitian setup.</p>
258) 
259)     <p>Assuming the verification happens on a Linux computer one first needs the
260)     <tt>mar-tools-linux*.zip</tt> out of the <tt>gitian-builder/inputs</tt>
261)     directory to remove the embedded signature(s). The steps to get the unsigned
262)     MAR file on a 64 bit Linux are</p>
263)     <pre>
264)     cd /path/to/MAR/file
265)     unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip

266)     export LD_LIBRARY_PATH=/path/to/MAR/file/mar-tools

267)     mar-tools/signmar -r your-signed-mar-file.mar your-unsigned-mar-file.mar</pre>
268)     <p>Now you can compare the SHA256 sum of <tt>your-unsigned-mar-file.mar</tt>

269)     with the one provided in the <tt>sha265sums-unsigned-build.txt</tt> or
270)     <tt>sha256sums-unsigned-build.incremental.txt</tt> as outlined in
271)     <a href="#BuildVerification">Verifying sha256sums (advancded)</a> above.</p>

272) 

273)   </div>
274)   <!-- END MAINCOL -->
275)   <div id = "sidecol">
276) #include "side.wmi"
277) #include "info.wmi"
278)   </div>
279)   <!-- END SIDECOL -->
280) </div>
281) <!-- END CONTENT -->