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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://en.wikipedia.org/wiki/Digital_signature">
22)     https://en.wikipedia.org/wiki/Digital_signature</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 to ensure that the software package
30)     that you have just downloaded is authentic. </p>

31) 
32)     <p>For many Tor users it is important to verify that the Tor software is authentic
33)     as they have very real adversaries who might try to give them a fake version
34)     of Tor.</p>

35) 

36)     <p>If the Tor package has been modified by some attacker it is not safe to use.
37)     It doesn't matter how secure and anonymous Tor is if you're not running the real Tor.</p>
38) 

39)     <p>Before you go ahead and download something, there are a few extra steps you
40)     should take to make sure you have downloaded an authentic version of Tor.</p>
41) 
42)     <h4>Always download Tor from torproject.org</h4>
43) 

44)     <p>There are a variety of attacks that can be used to make you download a fake
45)     version of Tor. For example, an attacker could trick you into thinking some other

46)     website is a great place to download Tor. You should

47)     always download Tor from <a href="https://www.torproject.org"><b>https</b>://www.torproject.org/</a>.</p>
48) 

49)     <h4>Always make sure you are browsing over https</h4>
50) 

51)     <p><a href="https://www.torproject.org">https://www.torproject.org/</a> uses https.
52)     Https is the secure version of the http protocol which uses encryption and authentication between your
53)     browser and the website. This makes it much harder for the attacker

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

55)     world block the Tor website, making users to download Tor <a href="<page
56)     docs/faq>#GetTor">somewhere else</a>.</p>
57) 
58)     <p>Large companies sometimes force employees to use a modified browser,

59)     so the company can listen in on all their browsing. We've even <a
60)     href="https://blog.torproject.org/blog/diginotar-debacle-and-what-you-should-do-about-it">seen</a>
61)     attackers who have the ability to trick your browser into thinking
62)     you're talking to the Tor website with https when you're not.</p>
63) 

64)     <h4>Always verify signatures of packages you have downloaded</h4>
65) 

66)     <p>Some software sites list <a

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

68)     hashes</a> alongside the software on their website, so users can
69)     verify that they downloaded the file without any errors. These
70)     "checksums" help you answer the question "Did I download this file
71)     correctly from whoever sent it to me?" They do a good job at making
72)     sure you didn't have any random errors in your download, but they
73)     don't help you figure out whether you were downloading it from the
74)     attacker. The better question to answer is: "Is this file that I
75)     just downloaded the file that Tor intended me to get?"</p>
76) 

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

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

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

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

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

87) 

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

90)     the package has been signed. Therefore every time a new file is uploaded a new
91)     signature is generated with a different date. As long as you have verified the
92)     signature you should not worry that the reported date may vary.
93)     </p>
94) 

95)     <h3>Windows</h3>

96)     <hr>

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

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

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

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

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

107)     (0x4E2C6E8793298290) by starting <i>cmd.exe</i> and typing:</p>

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

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

110)     is correct:</p>

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

112)     <p>You should see:</p>
113)     <pre>

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

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

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

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

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

127)     <p>Please substitute "Alice" with your own username.</p>

128)     <p>The output should say "Good signature": </p>
129)     <pre>

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

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

134)     Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290</pre>
135)     <p>Currently valid subkey fingerprints are:
136)     <pre>
137)     5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036

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

140)     <p>
141)     Notice that there is a warning because you haven't assigned a trust
142)     index to this person. This means that GnuPG verified that the key made
143)     that signature, but it's up to you to decide if that key really belongs
144)     to the developer. The best method is to meet the developer in person and
145)     exchange key fingerprints.
146)     </p>

147) 

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

149)     <hr>

150) 

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

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

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

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

156)     </p>

157) 

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

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

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

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

162) 

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

164) 

165)     <p>After importing the key, you can verify that the fingerprint
166)     is correct:</p>
167) 

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

169) 

170)     <p>You should see:</p>
171)     <pre>

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

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

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

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

181) 

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

183)     <pre>gpg --verify ~/Downloads/TorBrowser-<version-torbrowserbundleosx64>-osx64_en-US.dmg{.asc*,}</pre>
184) 

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

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

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

188) 

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

190) 

191)     <pre>

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

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

196)     Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290</pre> <p> Currently valid subkey fingerprints are:
197)     <pre>
198)     5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036

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

201)     <p>
202)     Notice that there is a warning because you haven't assigned a trust
203)     index to this person. This means that GnuPG verified that the key made
204)     that signature, but it's up to you to decide if that key really belongs
205)     to the developer. The best method is to meet the developer in person and
206)     exchange key fingerprints.
207)     </p>

208) 

209)     <p>
210)     If you're a Linux user and you're using the <b>Debian</b> Tor (not Tor
211)     Browser) packages, you should read the instructions on <a
212)     href="<page docs/debian>#packages">importing these keys to apt</a>.
213)     If you're using the <b>RPMs</b> (for Tor, not Tor Browser), you can
214)     manually verify the signatures on the RPM packages by
215)     <pre>rpm -K filename.rpm</pre>
216)     </p>

217) 
218)     <p>See <a

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

220)     to learn more about GnuPG.</p>
221) 
222)     <hr>

223) 

224)     <a id="BuildVerification"></a>
225)     <h3><a class="anchor" href="#BuildVerification">
226)     Verifying sha256sums (advanced)</a></h3>
227)     <hr>

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

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

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

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

237)        identical to the download.</p>
238) 
239)       <p>The steps below walk through this process:</p>
240) 
241)     <ul>

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

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

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

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

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

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

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

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

258)       <li>Verify the sha256sums-unsigned-build.txt file by executing this
259)       command:
260)       <pre>gpg --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt</pre></li>

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

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

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

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

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

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

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

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

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

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

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

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

285)     </ul>

286) 
287)     <p><a href="https://github.com/isislovecruft/scripts/blob/master/verify-gitian-builder-signatures">Scripts</a>

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

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

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

291) 
292)     <hr>
293) 
294)     <a id="MARVerification"></a>
295)     <h3><a class="anchor" href="#MARVerification">
296)     Verifying MAR files we ship (advanced)</a></h3>

297)     <hr>

298)     <p>Starting with Tor Browser 4.5a4 we sign our MAR files which helps
299)     securing our update process. The downside of this is the need for additional
300)     instructions to verify that the MAR files we ship are indeed the ones we
301)     produced with our Gitian setup.</p>
302) 
303)     <p>Assuming the verification happens on a Linux computer one first needs the
304)     <tt>mar-tools-linux*.zip</tt> out of the <tt>gitian-builder/inputs</tt>
305)     directory to remove the embedded signature(s). The steps to get the unsigned
306)     MAR file on a 64 bit Linux are</p>
307)     <pre>
308)     cd /path/to/MAR/file
309)     unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip

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

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

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

316) 

317)   </div>
318)   <!-- END MAINCOL -->
319)   <div id = "sidecol">
320) #include "side.wmi"
321) #include "info.wmi"
322)   </div>
323)   <!-- END SIDECOL -->
324) </div>
325) <!-- END CONTENT -->