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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)     <p>Digital signature is a process ensuring that a certain package was
16)     generated by its developers and has not been tampered with. Below we explain
17)     why it is important and how to verify that the Tor program you download is
18)     the one we have created and has not been modified by some attacker.</p>
19) 
20)     <p>Digital signature is a cryptographic mechanism. If you want to learn more
21)     about how it works see <a href="https://www.gnupg.org/documentation/">
22)     https://www.gnupg.org/documentation/</a>.</p>
23) 

24)     <h3>What is a signature and why should I check it?</h3>
25)     <hr>
26) 

27)     <p>How do you know that the Tor program you have is really the one we made?
28)     Digital signatures ensure that the package you are downloading was created by
29)     our developers. It uses a cryptographic mechanism which outputs a sequence of
30)     characters that is always the same unless the software has not been tampered
31)     with.</p>
32) 
33)     <p>For many Tor users it is important to verify that the Tor software is authentic
34)     as they have very real adversaries who might try to give them a fake version
35)     of Tor.</p>

36) 

37)     <p>If the Tor package has been modified by some attacker it is not safe to use.
38)     It doesn't matter how secure and anonymous Tor is if you're not running the real Tor.</p>
39) 
40)     <p>There are a variety of attacks that can be used to make you download a fake
41)     version of Tor. For example, an attacker could trick you into thinking some other

42)     website is a great place to download Tor. That's why you should

43)     always download Tor from <a href="https://www.torproject.org"><b>https</b>://www.torproject.org/</a>.</p>
44) 
45)     <p><a href="https://www.torproject.org">https://www.torproject.org/</a> uses https.
46)     Https is the secure version of the http protocol which uses encryption and authentication between your
47)     browser and the website. This makes it much harder for the attacker

48)     to modify your download. But it's not perfect. Some places in the

49)     world block the Tor website, making users to download Tor <a href="<page
50)     docs/faq>#GetTor">somewhere else</a>.</p>
51) 
52)     <p>Large companies sometimes force employees to use a modified browser,

53)     so the company can listen in on all their browsing. We've even <a
54)     href="https://blog.torproject.org/blog/diginotar-debacle-and-what-you-should-do-about-it">seen</a>
55)     attackers who have the ability to trick your browser into thinking
56)     you're talking to the Tor website with https when you're not.</p>
57) 
58)     <p>Some software sites list <a

59)     href="https://en.wikipedia.org/wiki/Cryptographic_hash_function">sha1

60)     hashes</a> alongside the software on their website, so users can
61)     verify that they downloaded the file without any errors. These
62)     "checksums" help you answer the question "Did I download this file
63)     correctly from whoever sent it to me?" They do a good job at making
64)     sure you didn't have any random errors in your download, but they
65)     don't help you figure out whether you were downloading it from the
66)     attacker. The better question to answer is: "Is this file that I
67)     just downloaded the file that Tor intended me to get?"</p>
68) 

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

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

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

76)     torbrowser-install-<version-torbrowserbundle>_en-US.exe is accompanied by
77)     torbrowser-install-<version-torbrowserbundle>_en-US.exe.asc. For a list

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

79) 

80)     <p>We now show how you can verify the downloaded file's digital signature on
81)     different operating systems. Please notice that a signature is dated the moment

82)     the package has been signed. Therefore every time a new file is uploaded a new
83)     signature is generated with a different date. As long as you have verified the
84)     signature you should not worry that the reported date may vary.
85)     </p>
86) 

87)     <h3>Windows</h3>

88)     <hr>

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

91)     href="https://gpg4win.org/download.html">https://gpg4win.org/download.html</a>.</p>

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

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

98)     <p>The Tor Browser team signs Tor Browser releases. Import its key

99)     (0x4E2C6E8793298290) by starting <i>cmd.exe</i> and typing:</p>

100)     <pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290</pre>

101)     <p>After importing the key, you can verify that the fingerprint

102)     is correct:</p>

103)     <pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --fingerprint 0x4E2C6E8793298290</pre>

104)     <p>You should see:</p>
105)     <pre>

106)     pub   4096R/93298290 2014-12-15
107)           Key fingerprint = EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
108)     uid                  Tor Browser Developers (signing key) <torbrowser@torproject.org>
109)     sub   4096R/F65C2036 2014-12-15
110)     sub   4096R/D40814E0 2014-12-15

111)     sub   4096R/C3C07136 2016-08-24

112) </pre>
113)     <p>To verify the signature of the package you downloaded, you will need
114)     to download the ".asc" file as well. Assuming you downloaded the
115)     package and its signature to your Desktop, run:</p>

116)     <pre>"C:\Program Files\Gnu\GnuPg\gpg.exe" --verify \
117)     C:\Users\Alice\Desktop\torbrowser-install-<version-torbrowserbundle>_en-US.exe.asc \

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

119)     <p>The output should say "Good signature": </p>
120)     <pre>

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

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

125)     Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290</pre>
126)     <p>Currently valid subkey fingerprints are:
127)     <pre>
128)     5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036

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

131)     <p>
132)     Notice that there is a warning because you haven't assigned a trust
133)     index to this person. This means that GnuPG verified that the key made
134)     that signature, but it's up to you to decide if that key really belongs
135)     to the developer. The best method is to meet the developer in person and
136)     exchange key fingerprints.
137)     </p>

138) 

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

140)     <hr>

141) 

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

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

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

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

147)     </p>

148) 

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

150)     your package. The Tor Browser team signs Tor Browser releases. Import its

151)     key (0x4E2C6E8793298290) by starting the terminal (under "Applications"

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

153) 

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

155) 

156)     <p>After importing the key, you can verify that the fingerprint
157)     is correct:</p>
158) 

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

160) 

161)     <p>You should see:</p>
162)     <pre>

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

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

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

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

172) 

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

174)     <pre>gpg --verify ~/Downloads/TorBrowser-<version-torbrowserbundleosx64>-osx64_en-US.dmg{.asc*,}</pre>
175) 

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

177)     <pre>gpg --verify tor-browser-linux64-<version-torbrowserbundlelinux64>_en-US.tar.xz.asc \

178)     tor-browser-linux64-<version-torbrowserbundlelinux64>_en-US.tar.xz</pre>

179) 

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

181) 

182)     <pre>

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

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

187)     Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290</pre> <p> Currently valid subkey fingerprints are:
188)     <pre>
189)     5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036

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

192)     <p>
193)     Notice that there is a warning because you haven't assigned a trust
194)     index to this person. This means that GnuPG verified that the key made
195)     that signature, but it's up to you to decide if that key really belongs
196)     to the developer. The best method is to meet the developer in person and
197)     exchange key fingerprints.
198)     </p>

199) 

200)     <p>
201)     If you're a Linux user and you're using the <b>Debian</b> Tor (not Tor
202)     Browser) packages, you should read the instructions on <a
203)     href="<page docs/debian>#packages">importing these keys to apt</a>.
204)     If you're using the <b>RPMs</b> (for Tor, not Tor Browser), you can
205)     manually verify the signatures on the RPM packages by
206)     <pre>rpm -K filename.rpm</pre>
207)     </p>

208) 
209)     <p>See <a

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

211)     to learn more about GnuPG.</p>
212) 
213)     <hr>

214) 

215)     <a id="BuildVerification"></a>
216)     <h3><a class="anchor" href="#BuildVerification">
217)     Verifying sha256sums (advanced)</a></h3>
218)     <hr>

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

221)        property</a> of Tor Browser 3.0 and later. Anyone can build
222)        Tor Browser on their own machine and produce a binary that is
223)        bit-for-bit identical to the binary we offer on the download page.

224)        Fortunately, it is not necessary for everyone to build Tor Browser

225)        locally to get this security. Verifying and comparing the signed list
226)        of <a href="https://en.wikipedia.org/wiki/Cryptographic_hash">hashes</a>
227)        will confirm that multiple people have built Tor Browsers

228)        identical to the download.</p>
229) 
230)       <p>The steps below walk through this process:</p>
231) 
232)     <ul>

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

237)       https://www.torproject.org/dist/torbrowser/</a>, for example in '<version-torbrowserbundlelinux64>'
238)       for Tor Browser <version-torbrowserbundlelinux64>.</li>

239)       <li>In case your operating system is adding the .txt extension
240)       automatically to the SHA256 sums signature file strip it again by running
241)       <pre>mv sha256sums-unsigned-build.txt.asc.txt sha256sums-unsigned-build.txt.asc</pre>

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

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

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

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

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

249)       <li>Verify the sha256sums-unsigned-build.txt file by executing this
250)       command:
251)       <pre>gpg --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt</pre></li>

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

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

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

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

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

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

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

265)       <p>On Linux you can run</p>
266)       <pre>sha256sum &lt;TOR BROWSER FILE NAME&gt;.tar.gz</pre>
267)       without having to download a utility. Note: this does not work for OS X
268)       yet due to Apple's codesigning requirement.</li>

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

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

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

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

276)     </ul>

277) 
278)     <p><a href="https://github.com/isislovecruft/scripts/blob/master/verify-gitian-builder-signatures">Scripts</a>

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

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

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

282) 
283)     <hr>
284) 
285)     <a id="MARVerification"></a>
286)     <h3><a class="anchor" href="#MARVerification">
287)     Verifying MAR files we ship (advanced)</a></h3>

288)     <hr>

289)     <p>Starting with Tor Browser 4.5a4 we sign our MAR files which helps
290)     securing our update process. The downside of this is the need for additional
291)     instructions to verify that the MAR files we ship are indeed the ones we
292)     produced with our Gitian setup.</p>
293) 
294)     <p>Assuming the verification happens on a Linux computer one first needs the
295)     <tt>mar-tools-linux*.zip</tt> out of the <tt>gitian-builder/inputs</tt>
296)     directory to remove the embedded signature(s). The steps to get the unsigned
297)     MAR file on a 64 bit Linux are</p>
298)     <pre>
299)     cd /path/to/MAR/file
300)     unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip

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

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

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

307) 

308)   </div>
309)   <!-- END MAINCOL -->
310)   <div id = "sidecol">
311) #include "side.wmi"
312) #include "info.wmi"
313)   </div>
314)   <!-- END SIDECOL -->
315) </div>
316) <!-- END CONTENT -->