2015-05-26 11:35:25 -04:00
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---
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layout: doc
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title: InstallSecurity
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permalink: /doc/InstallSecurity/
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redirect_from: /wiki/InstallSecurity/
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---
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# Installation Security Considerations #
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## Verifying the Qubes ISO ##
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You should [verify][] the PGP signature on your Qubes ISO before you install
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from it. However, if the machine on which you attempt the verification process
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is already compromised, it could falsely claim that a malicious ISO has a good
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signature. Therefore, in order to be certain that your Qubes ISO is trustworthy,
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you require a trustworthy machine. But how can you be certain *that* machine is
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trustworthy? Only by using another trusted machine, and so forth. This is a
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[classic problem][trusting-trust]. While various [solutions][countering] have
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been proposed, the point is that each user must ultimately make a choice about
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whether to trust that a file is non-malicious.
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## Choosing an Installation Medium ##
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So, after taking some measures to verify its integrity and authenticity, you've
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decided to trust your Qubes ISO. Great! Now you must decide what sort of medium
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on which to write it so that you can install from it. From a Qubes-specific
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security perspective, each has certain pros and cons.
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### USB Drives ###
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Pros:
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* Works via USB, including with a [USBVM][].
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* Non-fixed capacity. (Easy to find one on which the ISO can fit.)
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Cons:
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* Rewriteable. (If the drive is mounted to a compromised machine, the ISO could
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be maliciously altered after it has been written to the drive.)
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* Untrustworthy firmware. (Firmware can be malicious even if the drive is new.
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Plugging a drive with rewriteable firmware into a compromised machine can
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also [compromise the drive][BadUSB]. Installing from a compromised drive
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could compromise even a brand new Qubes installation.)
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### Optical Discs ###
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Pros:
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* Read-only available. (If you use read-only media, you don't have to worry
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about the ISO being maliciously altered after it has been written to the
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disc. You then have the option of verifying the signature on multiple
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different machines.)
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Cons:
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* Fixed capacity. (If the size of the ISO is larger than your disc, it will be
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inconvenient.)
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* Passthrough burning is not supported by Xen. (This mainly applies if you're
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upgrading from a previous version of Qubes.) Currently, the only options for
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burning optical discs in Qubes are:
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1. Use a USB optical drive.
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2. Attach a SATA optical drive to a secondary SATA controller, then assign
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this secondary SATA controller to an AppVM.
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2015-07-23 07:19:16 -04:00
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3. Use a SATA optical drive attached to dom0.
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2015-05-26 11:35:25 -04:00
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(Option 3 violates the Qubes security model since it entails transferring
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an untrusted ISO to dom0 in order to burn it to disc, which leaves only
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the other two options.)
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[verify]: https://www.qubes-os.org/doc/VerifyingSignatures/
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[trusting-trust]: http://www.acm.org/classics/sep95/
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[countering]: http://www.dwheeler.com/trusting-trust/
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[USBVM]: https://www.qubes-os.org/doc/SecurityGuidelines/#creating-and-using-a-usbvm
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[BadUSB]: https://srlabs.de/badusb/
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