Home » Verifying Signatures

How to verify signatures for packages

Digital signature is a process ensuring that a certain package was generated by its developers and has not been tampered with. Below we explain why it is important and how to verify that the Tor program you download is the one we have created and has not been modified by some attacker.

Digital signature is a cryptographic mechanism. If you want to learn more about how it works see https://en.wikipedia.org/wiki/Digital_signature.

What is a signature and why should I check it?

How do you know that the Tor program you have is really the one we made? Digital signatures ensure that the package you are downloading was created by our developers. It uses a cryptographic mechanism to ensure that the software package that you have just downloaded is authentic.

For many Tor users it is important to verify that the Tor software is authentic as they have very real adversaries who might try to give them a fake version of Tor.

If the Tor package has been modified by some attacker it is not safe to use. It doesn't matter how secure and anonymous Tor is if you're not running the real Tor.

Before you go ahead and download something, there are a few extra steps you should take to make sure you have downloaded an authentic version of Tor.

Always download Tor from torproject.org

There are a variety of attacks that can be used to make you download a fake version of Tor. For example, an attacker could trick you into thinking some other website is a great place to download Tor. You should always download Tor from https://www.torproject.org/.

Always make sure you are browsing over https

https://www.torproject.org/ uses https. Https is the secure version of the http protocol which uses encryption and authentication between your browser and the website. This makes it much harder for the attacker to modify your download. But it's not perfect. Some places in the world block the Tor website, making users to download Tor somewhere else.

Large companies sometimes force employees to use a modified browser, so the company can listen in on all their browsing. We've even seen attackers who have the ability to trick your browser into thinking you're talking to the Tor website with https when you're not.

Always verify signatures of packages you have downloaded

Some software sites list sha1 hashes alongside the software on their website, so users can verify that they downloaded the file without any errors. These "checksums" help you answer the question "Did I download this file correctly from whoever sent it to me?" They do a good job at making sure you didn't have any random errors in your download, but they don't help you figure out whether you were downloading it from the attacker. The better question to answer is: "Is this file that I just downloaded the file that Tor intended me to get?"

Where do I get the signatures and the keys that made them?

Each file on our download page is accompanied by a file with the same name as the package and the extension ".asc". These .asc files are GPG signatures. They allow you to verify the file you've downloaded is exactly the one that we intended you to get. For example, torbrowser-install-_en-US.exe is accompanied by torbrowser-install-_en-US.exe.asc. For a list of which developer signs which package, see our signing keys page.

We now show how you can verify the downloaded file's digital signature on different operating systems. Please notice that a signature is dated the moment the package has been signed. Therefore every time a new file is uploaded a new signature is generated with a different date. As long as you have verified the signature you should not worry that the reported date may vary.

Windows

First of all you need to have GnuPG installed before you can verify signatures. Download it from https://gpg4win.org/download.html.

Once it's installed, use GnuPG to import the key that signed your package. In order to verify the signature you will need to type a few commands in windows command-line, cmd.exe.

The Tor Browser team signs Tor Browser releases. Import its key (0x4E2C6E8793298290) by starting cmd.exe and typing:

gpg.exe --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290

After importing the key, you can verify that the fingerprint is correct:

gpg.exe --fingerprint 0x4E2C6E8793298290

You should see:

pub   rsa4096/0x4E2C6E8793298290 2014-12-15 [C] [expires: 2020-08-24]
      Key fingerprint = EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
uid                   [ unknown] Tor Browser Developers (signing key) 
sub   rsa4096/0xD1483FA6C3C07136 2016-08-24 [S] [expires: 2018-08-24]
      Key fingerprint = A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
sub   rsa4096/0xEB774491D9FF06E2 2018-05-26 [S] [expires: 2020-09-12]
      Key fingerprint = 1107 75B5 D101 FB36 BC6C  911B EB77 4491 D9FF 06E2

To verify the signature of the package you downloaded, you will need to download the ".asc" file as well. Assuming you downloaded the package and its signature to your Desktop, run:

gpg.exe --verify C:\Users\Alice\Desktop\torbrowser-install-_en-US.exe.asc

Please substitute "Alice" with your own username.

The output should say "Good signature":

gpg: assuming signed data in 'torbrowser-install-_en-US.exe'
gpg: Signature made Wed 15 Nov 2017 05:52:38 PM CET
gpg:                using RSA key 0xD1483FA6C3C07136
gpg: Good signature from "Tor Browser Developers (signing key) " [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
     Subkey fingerprint: A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
    Currently valid subkey fingerprints are:
    
    5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036
    BA1E E421 BBB4 5263 180E  1FC7 2E1A C68E D408 14E0
    A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136

    
    Notice that there is a warning because you haven't assigned a trust
    index to this person. This means that GnuPG verified that the key made
    that signature, but it's up to you to decide if that key really belongs
    to the developer. The best method is to meet the developer in person and
    exchange key fingerprints.
    

    Mac OS X and Linux
    

    You need to have GnuPG installed before you can verify
    signatures. If you are using Mac OS X, you can install it from https://www.gpgtools.org/. If you
    are using Linux, then it's probably you already have GnuPG in your
    system, as most Linux distributions come with it preinstalled.
    

    The next step is to use GnuPG to import the key that signed
    your package. The Tor Browser team signs Tor Browser releases. Import its
    key (0x4E2C6E8793298290) by starting the terminal (under "Applications"
    in Mac OS X) and typing:

    gpg --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290

    After importing the key, you can verify that the fingerprint
    is correct:

    gpg --fingerprint 0x4E2C6E8793298290

    You should see:
    pub   rsa4096/0x4E2C6E8793298290 2014-12-15 [C] [expires: 2020-08-24]
      Key fingerprint = EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
uid                   [ unknown] Tor Browser Developers (signing key) 
sub   rsa4096/0xD1483FA6C3C07136 2016-08-24 [S] [expires: 2018-08-24]
      Key fingerprint = A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
sub   rsa4096/0xEB774491D9FF06E2 2018-05-26 [S] [expires: 2020-09-12]
      Key fingerprint = 1107 75B5 D101 FB36 BC6C  911B EB77 4491 D9FF 06E2
    
    To verify the signature of the package you downloaded, you will need
    to download the ".asc" file as well. Assuming you downloaded the
    package and its signature to your Downloads folder, run:

    For Mac OS X users:

    gpg --verify ~/Downloads/TorBrowser--osx64_en-US.dmg{.asc*,}

    For Linux users (change 64 to 32 if you have the 32-bit package):

    gpg --verify tor-browser-linux64-_en-US.tar.xz.asc

    The output should say "Good signature":

    gpg: assuming signed data in 'tor-browser-linux64-_en-US.tar.xz'
gpg: Signature made Wed 15 Nov 2017 05:52:38 PM CET
gpg:                using RSA key 0xD1483FA6C3C07136
gpg: Good signature from "Tor Browser Developers (signing key) " [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
     Subkey fingerprint: A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
    
     Currently valid subkey fingerprints are:
    
    5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036
    BA1E E421 BBB4 5263 180E  1FC7 2E1A C68E D408 14E0
    A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136

    
    Notice that there is a warning because you haven't assigned a trust
    index to this person. This means that GnuPG verified that the key made
    that signature, but it's up to you to decide if that key really belongs
    to the developer. The best method is to meet the developer in person and
    exchange key fingerprints.
    

    
    If you're a Linux user and you're using the Debian Tor (not Tor
    Browser) packages, you should read the instructions on importing these keys to apt.
    If you're using the RPMs (for Tor, not Tor Browser), you can
    manually verify the signatures on the RPM packages by
    
rpm -K filename.rpm
    

    See https://www.gnupg.org/documentation/
    to learn more about GnuPG.

    

    
    
    Verifying sha256sums (advanced)
    
    Build reproducibility is a security
       property of Tor Browser 3.0 and later. Anyone can build
       Tor Browser on their own machine and produce a binary that is
       bit-for-bit identical to the binary we offer on the download page.
       Fortunately, it is not necessary for everyone to build Tor Browser
       locally to get this security. Verifying and comparing the signed list
       of hashes
       will confirm that multiple people have built Tor Browsers
       identical to the download.

      The steps below walk through this process:

    
      Download the Tor Browser package, the sha256sums-unsigned-build.txt
      file, and the sha256sums-unsigned-build.txt.asc signature file.
      They can all be found in the same directory under
      
      https://www.torproject.org/dist/torbrowser/, for example in ''
      for Tor Browser .
      In case your operating system is adding the .txt extension
      automatically to the SHA256 sums signature file strip it again by running
      mv sha256sums-unsigned-build.txt.asc.txt sha256sums-unsigned-build.txt.asc
      
Retrieve the signers' GPG keys. This can be done from the command
      line by entering something like
      gpg --keyserver keys.mozilla.org --recv-keys 0x4E2C6E8793298290
      (This will bring you the public part of the Tor Browser developers'
       signing key. Other developers' key IDs can be found on
      this
      page.)
      Verify the sha256sums-unsigned-build.txt file by executing this
      command:
      gpg --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt
      You should see a message like "Good signature from <DEVELOPER
      NAME>". If you don't, there is a problem. Try these steps again.
      If you want to verify a Windows Tor Browser package you need to first
      strip off the authenticode signature of it. Tools that can be used for
      this purpose are osslsigncode and
      delcert.exe.
      Assuming you have built e.g. osslsigncode on a Linux computer you can enter
      /path/to/your/osslsigncode remove-signature \
        /path/to/your/<TOR BROWSER FILE NAME>.exe <TOR BROWSER FILE NAME>.exe
      Now you can take the sha256sum of the Tor Browser package. On
      Windows you can use the 
      hashdeep utility and run
      C:\location\where\you\saved\hashdeep -c sha256sum <TOR BROWSER FILE NAME>.exe
      On Linux you can run
      sha256sum <TOR BROWSER FILE NAME>.tar.gz
      without having to download a utility. Note: this does not work for OS X
      yet due to Apple's codesigning requirement.
      You will see a string of letters and numbers.
      Open sha256sums-unsigned-build.txt in a text editor.
      Locate the name of the Tor Browser file you downloaded.
      Compare the string of letters and numbers to the left of your
      filename with the string of letters and numbers that appeared
      on your command line. If they match, you've successfully verified the
      build.
    

    Scripts
    to automate
    these steps have been written, but to use them you will need to modify
    them yourself with the latest Tor Browser filename.

    

    
    
    Verifying MAR files we ship (advanced)
    
    Starting with Tor Browser 4.5a4 we sign our MAR files which helps
    securing our update process. The downside of this is the need for additional
    instructions to verify that the MAR files we ship are indeed the ones we
    produced with our rbm setup.

    Assuming the verification happens on a Linux computer one first needs the
    mar-tools-linux*.zip out of the gitian-builder/inputs
    directory to remove the embedded signature(s). The steps to get the unsigned
    MAR file on a 64 bit Linux are
        cd /path/to/MAR/file
    unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip
    export LD_LIBRARY_PATH=/path/to/MAR/file/mar-tools
    mar-tools/signmar -r your-signed-mar-file.mar your-unsigned-mar-file.mar
    Now you can compare the SHA256 sum of your-unsigned-mar-file.mar
    with the one provided in the sha265sums-unsigned-build.txt or
    sha256sums-unsigned-build.incremental.txt as outlined in
    Verifying sha256sums (advancded) above.

#include "side.wmi" #include "info.wmi"