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qubes-doc/common-tasks/backup-emergency-restore-v4.md
Andrew David Wong 78b185edc5
Explain how to decrypt qubes.xml.000.enc 
Closes QubesOS/qubes-issues#4728
2019-03-02 01:37:08 -06:00

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layout title permalink redirect_from
doc Emergency Backup Recovery (v4) /doc/backup-emergency-restore-v4/
/en/doc/backup-emergency-restore-v4/
/doc/BackupEmergencyRestoreV4/

Emergency Backup Recovery without Qubes (v4)

This page describes how to perform an emergency restore of a backup created on Qubes R4.X (which uses backup format version 4).

The Qubes backup system has been designed with emergency disaster recovery in mind. No special Qubes-specific tools are required to access data backed up by Qubes. In the event a Qubes system is unavailable, you can access your data on any GNU/Linux system with the following procedure.

Required scrypt Utility

In Qubes 4.X, backups are encrypted and integrity-protected with scrypt. You will need a copy of this utility in order to access your data. Since scrypt is not pre-installed on every GNU/Linux system, it is strongly recommended that you store a copy of it with your backups. If your distribution has scrypt packaged (e.g., Debian), you can install the package in the standard way using your distribution's package manager. Otherwise, you'll need to obtain a compiled binary (instructions below) or compile the program from source yourself. (Don't forget to verify signatures first!) Note that versions of scrypt up to 1.2.0 (inclusive) do not support the -P option for easier scripting, which means you'll need to enter the passphrase for each file separately, instead of using echo ... | scrypt.

Here are instructions for obtaining a compiled scrypt binary. This example uses an RPM-based system (Fedora), but the same general procedure should work on any GNU/Linux system.

  1. If you're not on Qubes 4.X, get and verify the Release 4 Signing Key.

  2. If you're not on Qubes 4.X, import the Release 4 Signing Key.

    [user@restore ~]$ sudo rpm --import qubes-release-4-signing-key.asc

  3. Download the scrypt RPM.

    [user@restore ~]$ dnf download scrypt

    or, if that doesn't work:

    [user@restore ~]$ curl -O https://yum.qubes-os.org/r4.0/current/vm/fc28/rpm/scrypt-1.2.1-1.fc28.x86_64.rpm

  4. Verify the signature on the scrypt RPM.

    [user@restore ~]$ rpm -K scrypt-*.rpm 
scrypt-*.rpm: digests signatures OK

    The message digests signatures OK means that both the digest (i.e., the output of a hash function) and PGP signature verification were successful.

  5. Install rpmdevtools.

    [user@restore ~]$ sudo dnf install rpmdevtools

  6. Extract the scrypt binary from the RPM.

    [user@restore ~]$ rpmdev-extract scrypt-*.rpm

  7. (Optional) Create an alias for the new binary.

    [user@restore ~]$ alias scrypt="scrypt-*/usr/bin/scrypt"

Emergency Recovery Instructions

Note: In the following example, the backup file is both encrypted and compressed.

  1. Untar the main backup file.

    [user@restore ~]$ tar -i -xvf qubes-backup-2015-06-05T123456
backup-header
backup-header.hmac
qubes.xml.000.enc
vm1/private.img.000.enc
vm1/private.img.001.enc
vm1/private.img.002.enc
vm1/icon.png.000.enc
vm1/firewall.xml.000.enc
vm1/whitelisted-appmenus.list.000.enc
dom0-home/dom0user.000.enc

    To extract only specific VMs: Each VM in the backup file has its path listed in qubes.xml.000.enc. Decrypt it. (In this example, the password is password.)

    [user@restore ~]$ cat backup-header | grep backup-id
backup-id=20190128T123456-1234
[user@restore ~]$ scrypt dec -P qubes.xml.000.enc qubes.xml.000
Please enter passphrase: 20190128T123456-1234!qubes.xml.000!password
[user@restore ~]$ tar -i -xvf qubes.xml.000

    Now that you have the decrypted qubes.xml.000 file, search for the backup-path property inside of it. With the backup-path, extract only the files necessary for your VM (vmX).

    [user@restore ~]$ tar -i -xvf qubes-backup-2015-06-05T123456 \
    backup-header backup-header.hmac vmX/

  2. Set the backup passphrase environment variable. While this isn't strictly required, it will be handy later and will avoid saving the passphrase in the shell's history.

    [user@restore ~]$ read backup_pass

  3. Verify the integrity of backup-header. For compatibility reasons, backup-header.hmac is an encrypted and integrity protected version of backup-header.

    [user@restore ~]$ set +H
[user@restore ~]$ echo "backup-header!$backup_pass" |\
    scrypt dec -P backup-header.hmac backup-header.verified && \
    diff -qs backup-header backup-header.verified
Files backup-header and backup-header.verified are identical

    Note: If this command fails, it may be that the backup was tampered with or is in a different format. In the latter case, look inside backup-header at the version field. If it contains a value other than version=4, go to the instructions for that format version:

  4. Read backup-header:

    [user@restore ~]$ cat backup-header
version=4
encrypted=True
compressed=True
compression-filter=gzip
backup_id=20161020T123455-1234

  5. Set backup_id to the value in the last line of backup-header:

    [user@restore ~]$ backup_id=20161020T123455-1234

  6. Verify the integrity of and decrypt the private.img file that houses your data.

    [user@restore ~]$ for f_enc in vm1/private.img.???.enc; do \
    f_dec=${f_enc%.enc}; \
    echo "$backup_id!$f_dec!$backup_pass" | scrypt dec -P $f_enc $f_dec || break; \
    done

    Note: If this command fails, it is likely that the backup is corrupted or has been tampered with.

  7. Decompress and untar the decrypted private.img file.

    [user@restore ~]$ cat vm1/private.img.??? | gzip -d | tar -xv
vm1/private.img

    Note: If your backup was compressed with a program other than gzip, you must substitute the correct compression program. This information is contained in backup-header (see step 4). For example, if you used bzip2, then you should do this:

    [user@restore vm1]$ mv private.img.dec private.img.dec.bz2
[user@restore vm1]$ bunzip2 private.img.dec.bz2

  8. Mount private.img and access your data.

    [user@restore vm1]$ sudo mkdir /mnt/img
[user@restore vm1]$ sudo mount -o loop vm1/private.img /mnt/img/
[user@restore vm1]$ cat /mnt/img/home/user/your_data.txt
This data has been successfully recovered!

  9. Success! If you wish to recover data from more than one VM in your backup, simply repeat steps 6--8 for each additional VM.

    Note: You may wish to store a copy of these instructions with your Qubes backups in the event that you fail to recall the above procedure while this web page is inaccessible. All Qubes documentation, including this page, is available in plain text format in the following Git repository:

    https://github.com/QubesOS/qubes-doc.git