crypto-sdcard (regular edition)

Configuration files for unlocking and mounting encrypted SD-cards, using udev, udisks2, polkit and systemd

Preface

Note that for devices, which need to load Qualcomm's qcrypto kernel module in order to support modern cryptographic schemes as e.g. XTS (plus it is faster and more energy efficient), a separate "qcrypto edition" is provided. Only SailfishOS on the Jolla 1 (sbj) is known to provide the qcrypto.ko, hence currently it is the only device supported by the "qcrypto edition".
Thus for all other devices (i.e., on those where find /lib/modules/ -name qcrypto.ko yields nothing), this regular edition shall be used.

Extensively tested with systemd 225 (which includes udev), udisks2 2.7.5 and polkit 0.104 (e.g., SailfishOS since version 2.2.0, which provides aforementioned software) and newer versions.
Built RPMs are available in the release section and for easy installation under SailfishOS at OpenRepos.

The necessary steps to prepare an SD-card (or any other removable storage) are described at GitLab (original version at Together.Jolla.com).
Note that the "key"-files reside unencrypted on fixed, internal mass storage, as mobile devices usually have only a single user, who unlocks the whole device.
Thus crypto-sdcard solely protects "data at rest" on SD-cards and other removable storage, i.e. specifically when the device is locked or switched off (and the SD-card may be taken out).

Features

• These configuration files do not alter, replace or delete any extant files.
• Support of encrypted partitions and whole devices.
• Support for (µ)SD-cards and USB-attached storage (if supported by device hardware and Operating System).
• Support for Cryptsetup LUKS and Cryptsetup "plain".
  • Note that SailfishOS just recently (with v3.0.3) switched to Cryptsetup 2, and so did most (desktop) Linux distributions. For interoperability with extant Linux installations and commonality with SailfishOS before v3.0.3, which provide Cryptsetup 1.x (therefore only support LUKSv1 headers), the "partitioning guide" (originally at TJC) aims at creating LUKSv1 headers.
  • As Cryptsetup LUKS reads the cryptography parameters from the LUKS header and Cryptsetup 2 supports both v1 and v2 headers, crypto-sdcard shall work fine with any LUKS header version and parameters, which are valid for the installed Cryptsetup version.
  • For Cryptsetup "plain" (only to be used, when "plausible deniability" is a must), crypto-sdcard has to provide the cryptography parameters and uses "-h sha1 -s 256 -c aes-xts-plain" by default. While these parameters are optimised for speed, low power consumption, interoperability and sufficiently strong security for the next decade (including the specific use of SHA1 for hashing a pass-file down to 160 bits), other parameters may be set for unlocking Cryptsetup "plain" in /etc/systemd/system/cryptosd-plain@.service.
  • Since crypto-sdcard 1.3.4, the parsing of "key"-files in "plain" mode is enhanced.
    This change requires to convert extant "key"-files for "plain" mode.
    New "plain" "containers" shall be created slightly differently now, in order to take advantage of this enhancement.
• Start mounting encrypted (partitions on) SD-card via udisks at the earliest sensible time: Right after udisks2.service has started.
• Unmount before udisks2.service begins stopping, hence achieving a clean unmount.
• Also do not use SailfishOS' udisksctl-user script for unmounting (because it cannot work at the time ExecStop is executed), which is installed and used by SailfishOS since its release 3.2.1, and was also used by crypto-sdcard versions 1.1-1 to 1.3.1-5; see details here.
• Since v1.3.4, overhauled in v1.5.1: Use Systemd EnvironmentFiles, allowing administrators to easily set options.
• Ensure, that AlienDalvik (specifically alien-service-manager.service) begins starting after mounting succeeded, to allow for android_storage on SD-card.
  Even more importantly (i.e., also relevant for devices without "android_storage on SD-card") this also ensures, that unmounting occurs only after AlienDalvik has completely stopped.
  Nevertheless, these configuration files are also applicable to devices without AlienDalvik installed.
• Boot time is not significantly prolonged, as unlocking encrypted partitions per Cryptsetup occurs in parallel to starting udisks2.service; after both succeeded, all mount operations are also started concurrently.

Version history

This is a coarse changelog covering the most relevant changes for each minor release. The detailed changes of each point release are denoted on the releases page.

• Planned for v2.0 and later
  The "key"-file path and names are ultimately settled on (please rename your "key"-files accordingly):
  • For Cryptsetup LUKS: /etc/amount-enc/<UUID>
  • For Cryptsetup "plain": /etc/amount-enc/<device-name>
  • A specific <UUID> can be obtained by executing blkid -c /dev/null -s UUID -o value /dev/<device-name> with e.g. mmcblk1p2 as <device-name>.
• v1.7
  Completely re-wrote the Polkit rule file. Also document the awkward Polkit configuration file format situation in On-Poklkit.md.
  _{Introduce units for manual mounting (and implicit, automatic unlocking / opening of a "crypto container"), which work in "rescue" (Systemd's single user) target / mode: mnt-cryptosd-luks@<UUID>.service and mnt-cryptosd-plain@<device-name>.service}
• v1.6
  Refactor and vastly enhance the Udev rule file.
• v1.5
  Re-establish support for SailfishOS 2.2.0 to 3.2.0 in order to bring recently introduced features to older SailfishOS releases.
  Change license from MIT to LGPL-2.1-only.
• v1.4
  Reintegrated the "sbj edition"'s git repository into this one as branch qcrypto.
  Enhance the parsing of "key"-files in "plain" mode. This change requires to convert extant "key"-files for "plain" mode, see details. New "plain" partitions shall be created slightly differently now, in order to take advantage of this enhancement.
• v1.3
  Mounting is now restricted to users, who belong to the Unix-group media_rw, which is the case for the user nemo since some SailfishOS release before v3.2.1 and after v2.2.1 (unable to assess which one), or the defaultuser on freshly installed devices (since SailfishOS 3.4.0).
  Significantly altered versioning scheme, git tags naming and archive file (tarball) names, again: This time to accommodate for multiple release variants per version in order to serve different SailfishOS releases from one repository easily. For details see the document "Release version format, RPM dependencies and Git workflow".
• v1.2
  Significantly altered versioning scheme, git tags naming and archive file names. For details see the release information.
• v1.1
  Following the changes in SFOS-next to allow any interactive user (i.e., not just nemo) to mount an SD-card. Hence v1.1 requires at least SailfishOS 3.2.1.
  Note that mounting is still restricted to users, who belong to the Unix-group system, in contrast to e.g., mount-sdcard.
• v1.0
  Due to another round of significant spec-file changes (completely removed SalifishOS dependencies and all %post scriptlets), increasing the version number again.
• v0.6
  A few small, but significant enhancements (since v0.5-5) are finally reflected in another version number increase.
  "Key"-file path and names are now:
  • For Cryptsetup LUKS: /etc/crypto-sdcard/crypto_luks_<UUID>.key (since v0.3)
  • For Cryptsetup "plain": /etc/crypto-sdcard/crypto_plain_<device-name>.key (since v0.5-7)
  • A specific <UUID> can be obtained by executing blkid -s UUID -o value /dev/<device-name> with e.g. mmcblk1p2 as <device-name>.
• v0.5
  Although the installed configuration files are unaltered since v0.4-3, the spec-file ("RPM packaging") changes have been significant, so it ultimately earns an increased version number.
• v0.4
  Optimise configuration file names.
  Provide RPM spec file.
• v0.3
  Switch to a UUID-based "key"-file naming scheme for LUKS partitions to allow for swapping encrypted SD-cards easily and moved "key"-files into a directory. Missed to properly implement this change for "plain" partitions, as they have no UUID!
  Hence the "key"-file path and names have changed again (please rename your "key"-files accordingly):
  • For Cryptsetup LUKS: /etc/crypto-sdcard/crypto_luks_<UUID>.key
  • For Cryptsetup "plain": /etc/crypto-sdcard/crypto_plain_.key
• v0.2
  Fix automatic mounting of DM-Crypt "plain" partitions.
  "Key"-file path and names are altered (please rename your "key"-files accordingly):
  • For Cryptsetup LUKS: /etc/crypto_luks_<device>.key, e.g. /etc/crypto_luks_mmcblk1p2.key
  • For Cryptsetup "plain": /etc/crypto_plain_<device>.key, e.g. /etc/crypto_plain_mmcblk1p2.key
• v0.1
  Initial check-in of the last version at TJC.
  "Key"-file path and names are /etc/<device>.key, e.g. /etc/mmcblk1p2.key