514 lines
18 KiB
Nix
514 lines
18 KiB
Nix
{ config, lib, pkgs, ... }:
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with lib;
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let
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luks = config.boot.initrd.luks;
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openCommand = name': { name, device, header, keyFile, keyFileSize, allowDiscards, yubikey, fallbackToPassword, ... }: assert name' == name; ''
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# Wait for a target (e.g. device, keyFile, header, ...) to appear.
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wait_target() {
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local name="$1"
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local target="$2"
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if [ ! -e $target ]; then
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echo -n "Waiting 10 seconds for $name $target to appear"
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local success=false;
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for try in $(seq 10); do
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echo -n "."
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sleep 1
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if [ -e $target ]; then success=true break; fi
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done
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if [ $success = true ]; then
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echo " - success";
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else
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echo " - failure";
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fi
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fi
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}
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# Wait for luksRoot (and optionally keyFile and/or header) to appear, e.g.
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# if on a USB drive.
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wait_target "device" ${device}
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${optionalString (keyFile != null) ''
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wait_target "key file" ${keyFile}
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''}
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${optionalString (header != null) ''
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wait_target "header" ${header}
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''}
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open_normally() {
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echo luksOpen ${device} ${name} ${optionalString allowDiscards "--allow-discards"} \
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${optionalString (header != null) "--header=${header}"} \
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> /.luksopen_args
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${optionalString (keyFile != null) ''
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${optionalString fallbackToPassword "if [ -e ${keyFile} ]; then"}
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echo " --key-file=${keyFile} ${optionalString (keyFileSize != null) "--keyfile-size=${toString keyFileSize}"}" \
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>> /.luksopen_args
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${optionalString fallbackToPassword ''
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else
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echo "keyfile ${keyFile} not found -- fallback to interactive unlocking"
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fi
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''}
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''}
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cryptsetup-askpass
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rm /.luksopen_args
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}
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${optionalString (luks.yubikeySupport && (yubikey != null)) ''
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rbtohex() {
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( od -An -vtx1 | tr -d ' \n' )
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}
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hextorb() {
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( tr '[:lower:]' '[:upper:]' | sed -e 's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs printf )
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}
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open_yubikey() {
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# Make all of these local to this function
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# to prevent their values being leaked
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local salt
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local iterations
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local k_user
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local challenge
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local response
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local k_luks
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local opened
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local new_salt
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local new_iterations
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local new_challenge
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local new_response
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local new_k_luks
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mkdir -p ${yubikey.storage.mountPoint}
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mount -t ${yubikey.storage.fsType} ${toString yubikey.storage.device} ${yubikey.storage.mountPoint}
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salt="$(cat ${yubikey.storage.mountPoint}${yubikey.storage.path} | sed -n 1p | tr -d '\n')"
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iterations="$(cat ${yubikey.storage.mountPoint}${yubikey.storage.path} | sed -n 2p | tr -d '\n')"
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challenge="$(echo -n $salt | openssl-wrap dgst -binary -sha512 | rbtohex)"
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response="$(ykchalresp -${toString yubikey.slot} -x $challenge 2>/dev/null)"
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for try in $(seq 3); do
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${optionalString yubikey.twoFactor ''
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echo -n "Enter two-factor passphrase: "
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read -s k_user
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echo
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''}
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if [ ! -z "$k_user" ]; then
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k_luks="$(echo -n $k_user | pbkdf2-sha512 ${toString yubikey.keyLength} $iterations $response | rbtohex)"
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else
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k_luks="$(echo | pbkdf2-sha512 ${toString yubikey.keyLength} $iterations $response | rbtohex)"
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fi
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echo -n "$k_luks" | hextorb | cryptsetup luksOpen ${device} ${name} ${optionalString allowDiscards "--allow-discards"} --key-file=-
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if [ $? == "0" ]; then
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opened=true
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break
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else
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opened=false
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echo "Authentication failed!"
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fi
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done
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if [ "$opened" == false ]; then
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umount ${yubikey.storage.mountPoint}
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echo "Maximum authentication errors reached"
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exit 1
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fi
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echo -n "Gathering entropy for new salt (please enter random keys to generate entropy if this blocks for long)..."
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for i in $(seq ${toString yubikey.saltLength}); do
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byte="$(dd if=/dev/random bs=1 count=1 2>/dev/null | rbtohex)";
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new_salt="$new_salt$byte";
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echo -n .
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done;
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echo "ok"
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new_iterations="$iterations"
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${optionalString (yubikey.iterationStep > 0) ''
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new_iterations="$(($new_iterations + ${toString yubikey.iterationStep}))"
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''}
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new_challenge="$(echo -n $new_salt | openssl-wrap dgst -binary -sha512 | rbtohex)"
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new_response="$(ykchalresp -${toString yubikey.slot} -x $new_challenge 2>/dev/null)"
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if [ ! -z "$k_user" ]; then
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new_k_luks="$(echo -n $k_user | pbkdf2-sha512 ${toString yubikey.keyLength} $new_iterations $new_response | rbtohex)"
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else
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new_k_luks="$(echo | pbkdf2-sha512 ${toString yubikey.keyLength} $new_iterations $new_response | rbtohex)"
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fi
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mkdir -p ${yubikey.ramfsMountPoint}
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# A ramfs is used here to ensure that the file used to update
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# the key slot with cryptsetup will never get swapped out.
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# Warning: Do NOT replace with tmpfs!
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mount -t ramfs none ${yubikey.ramfsMountPoint}
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echo -n "$new_k_luks" | hextorb > ${yubikey.ramfsMountPoint}/new_key
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echo -n "$k_luks" | hextorb | cryptsetup luksChangeKey ${device} --key-file=- ${yubikey.ramfsMountPoint}/new_key
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if [ $? == "0" ]; then
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echo -ne "$new_salt\n$new_iterations" > ${yubikey.storage.mountPoint}${yubikey.storage.path}
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else
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echo "Warning: Could not update LUKS key, current challenge persists!"
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fi
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rm -f ${yubikey.ramfsMountPoint}/new_key
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umount ${yubikey.ramfsMountPoint}
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rm -rf ${yubikey.ramfsMountPoint}
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umount ${yubikey.storage.mountPoint}
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}
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${optionalString (yubikey.gracePeriod > 0) ''
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echo -n "Waiting ${toString yubikey.gracePeriod} seconds as grace..."
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for i in $(seq ${toString yubikey.gracePeriod}); do
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sleep 1
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echo -n .
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done
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echo "ok"
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''}
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yubikey_missing=true
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ykinfo -v 1>/dev/null 2>&1
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if [ $? != "0" ]; then
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echo -n "waiting 10 seconds for yubikey to appear..."
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for try in $(seq 10); do
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sleep 1
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ykinfo -v 1>/dev/null 2>&1
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if [ $? == "0" ]; then
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yubikey_missing=false
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break
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fi
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echo -n .
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done
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echo "ok"
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else
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yubikey_missing=false
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fi
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if [ "$yubikey_missing" == true ]; then
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echo "no yubikey found, falling back to non-yubikey open procedure"
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open_normally
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else
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open_yubikey
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fi
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''}
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# open luksRoot and scan for logical volumes
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${optionalString ((!luks.yubikeySupport) || (yubikey == null)) ''
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open_normally
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''}
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'';
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preLVM = filterAttrs (n: v: v.preLVM) luks.devices;
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postLVM = filterAttrs (n: v: !v.preLVM) luks.devices;
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in
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{
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options = {
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boot.initrd.luks.mitigateDMAAttacks = mkOption {
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type = types.bool;
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default = true;
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description = ''
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Unless enabled, encryption keys can be easily recovered by an attacker with physical
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access to any machine with PCMCIA, ExpressCard, ThunderBolt or FireWire port.
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More information is available at <link xlink:href="http://en.wikipedia.org/wiki/DMA_attack"/>.
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This option blacklists FireWire drivers, but doesn't remove them. You can manually
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load the drivers if you need to use a FireWire device, but don't forget to unload them!
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'';
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};
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boot.initrd.luks.cryptoModules = mkOption {
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type = types.listOf types.str;
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default =
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[ "aes" "aes_generic" "blowfish" "twofish"
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"serpent" "cbc" "xts" "lrw" "sha1" "sha256" "sha512"
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(if pkgs.stdenv.system == "x86_64-linux" then "aes_x86_64" else "aes_i586")
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];
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description = ''
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A list of cryptographic kernel modules needed to decrypt the root device(s).
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The default includes all common modules.
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'';
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};
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boot.initrd.luks.forceLuksSupportInInitrd = mkOption {
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type = types.bool;
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default = false;
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internal = true;
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description = ''
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Whether to configure luks support in the initrd, when no luks
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devices are configured.
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'';
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};
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boot.initrd.luks.devices = mkOption {
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default = { };
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example = { "luksroot".device = "/dev/disk/by-uuid/430e9eff-d852-4f68-aa3b-2fa3599ebe08"; };
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description = ''
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The encrypted disk that should be opened before the root
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filesystem is mounted. Both LVM-over-LUKS and LUKS-over-LVM
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setups are supported. The unencrypted devices can be accessed as
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<filename>/dev/mapper/<replaceable>name</replaceable></filename>.
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'';
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type = with types; loaOf (submodule (
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{ name, ... }: { options = {
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name = mkOption {
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visible = false;
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default = name;
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example = "luksroot";
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type = types.str;
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description = "Name of the unencrypted device in <filename>/dev/mapper</filename>.";
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};
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device = mkOption {
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example = "/dev/disk/by-uuid/430e9eff-d852-4f68-aa3b-2fa3599ebe08";
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type = types.str;
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description = "Path of the underlying encrypted block device.";
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};
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header = mkOption {
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default = null;
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example = "/root/header.img";
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type = types.nullOr types.str;
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description = ''
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The name of the file or block device that
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should be used as header for the encrypted device.
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'';
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};
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keyFile = mkOption {
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default = null;
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example = "/dev/sdb1";
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type = types.nullOr types.str;
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description = ''
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The name of the file (can be a raw device or a partition) that
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should be used as the decryption key for the encrypted device. If
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not specified, you will be prompted for a passphrase instead.
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'';
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};
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keyFileSize = mkOption {
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default = null;
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example = 4096;
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type = types.nullOr types.int;
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description = ''
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The size of the key file. Use this if only the beginning of the
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key file should be used as a key (often the case if a raw device
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or partition is used as key file). If not specified, the whole
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<literal>keyFile</literal> will be used decryption, instead of just
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the first <literal>keyFileSize</literal> bytes.
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'';
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};
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# FIXME: get rid of this option.
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preLVM = mkOption {
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default = true;
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type = types.bool;
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description = "Whether the luksOpen will be attempted before LVM scan or after it.";
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};
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allowDiscards = mkOption {
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default = false;
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type = types.bool;
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description = ''
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Whether to allow TRIM requests to the underlying device. This option
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has security implications; please read the LUKS documentation before
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activating it.
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'';
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};
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fallbackToPassword = mkOption {
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default = false;
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type = types.bool;
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description = ''
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Whether to fallback to interactive passphrase prompt if the keyfile
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cannot be found. This will prevent unattended boot should the keyfile
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go missing.
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'';
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};
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yubikey = mkOption {
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default = null;
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description = ''
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The options to use for this LUKS device in Yubikey-PBA.
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If null (the default), Yubikey-PBA will be disabled for this device.
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'';
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type = with types; nullOr (submodule {
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options = {
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twoFactor = mkOption {
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default = true;
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type = types.bool;
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description = "Whether to use a passphrase and a Yubikey (true), or only a Yubikey (false).";
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};
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slot = mkOption {
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default = 2;
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type = types.int;
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description = "Which slot on the Yubikey to challenge.";
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};
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saltLength = mkOption {
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default = 16;
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type = types.int;
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description = "Length of the new salt in byte (64 is the effective maximum).";
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};
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keyLength = mkOption {
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default = 64;
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type = types.int;
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description = "Length of the LUKS slot key derived with PBKDF2 in byte.";
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};
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iterationStep = mkOption {
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default = 0;
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type = types.int;
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description = "How much the iteration count for PBKDF2 is increased at each successful authentication.";
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};
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gracePeriod = mkOption {
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default = 2;
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type = types.int;
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description = "Time in seconds to wait before attempting to find the Yubikey.";
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};
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ramfsMountPoint = mkOption {
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default = "/crypt-ramfs";
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type = types.str;
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description = "Path where the ramfs used to update the LUKS key will be mounted during early boot.";
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};
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/* TODO: Add to the documentation of the current module:
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Options related to the storing the salt.
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*/
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storage = {
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device = mkOption {
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default = "/dev/sda1";
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type = types.path;
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description = ''
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An unencrypted device that will temporarily be mounted in stage-1.
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Must contain the current salt to create the challenge for this LUKS device.
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'';
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};
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fsType = mkOption {
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default = "vfat";
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type = types.str;
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description = "The filesystem of the unencrypted device.";
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};
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mountPoint = mkOption {
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default = "/crypt-storage";
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type = types.str;
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description = "Path where the unencrypted device will be mounted during early boot.";
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};
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path = mkOption {
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default = "/crypt-storage/default";
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type = types.str;
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description = ''
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Absolute path of the salt on the unencrypted device with
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that device's root directory as "/".
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'';
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};
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};
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};
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});
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};
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}; }));
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};
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boot.initrd.luks.yubikeySupport = mkOption {
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default = false;
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type = types.bool;
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description = ''
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Enables support for authenticating with a Yubikey on LUKS devices.
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See the NixOS wiki for information on how to properly setup a LUKS device
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and a Yubikey to work with this feature.
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'';
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};
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};
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config = mkIf (luks.devices != {} || luks.forceLuksSupportInInitrd) {
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# actually, sbp2 driver is the one enabling the DMA attack, but this needs to be tested
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boot.blacklistedKernelModules = optionals luks.mitigateDMAAttacks
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["firewire_ohci" "firewire_core" "firewire_sbp2"];
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# Some modules that may be needed for mounting anything ciphered
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boot.initrd.availableKernelModules = [ "dm_mod" "dm_crypt" "cryptd" "input_leds" ]
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++ luks.cryptoModules
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# workaround until https://marc.info/?l=linux-crypto-vger&m=148783562211457&w=4 is merged
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# remove once 'modprobe --show-depends xts' shows ecb as a dependency
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++ (if builtins.elem "xts" luks.cryptoModules then ["ecb"] else []);
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# copy the cryptsetup binary and it's dependencies
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boot.initrd.extraUtilsCommands = ''
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copy_bin_and_libs ${pkgs.cryptsetup}/bin/cryptsetup
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cat > $out/bin/cryptsetup-askpass <<EOF
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#!$out/bin/sh -e
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if [ -e /.luksopen_args ]; then
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cryptsetup \$(cat /.luksopen_args)
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killall -q cryptsetup
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else
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echo "Passphrase is not requested now"
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exit 1
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fi
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EOF
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chmod +x $out/bin/cryptsetup-askpass
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${optionalString luks.yubikeySupport ''
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copy_bin_and_libs ${pkgs.yubikey-personalization}/bin/ykchalresp
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copy_bin_and_libs ${pkgs.yubikey-personalization}/bin/ykinfo
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copy_bin_and_libs ${pkgs.openssl.bin}/bin/openssl
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cc -O3 -I${pkgs.openssl.dev}/include -L${pkgs.openssl.out}/lib ${./pbkdf2-sha512.c} -o pbkdf2-sha512 -lcrypto
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strip -s pbkdf2-sha512
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copy_bin_and_libs pbkdf2-sha512
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mkdir -p $out/etc/ssl
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cp -pdv ${pkgs.openssl.out}/etc/ssl/openssl.cnf $out/etc/ssl
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cat > $out/bin/openssl-wrap <<EOF
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#!$out/bin/sh
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export OPENSSL_CONF=$out/etc/ssl/openssl.cnf
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$out/bin/openssl "\$@"
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EOF
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chmod +x $out/bin/openssl-wrap
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''}
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'';
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boot.initrd.extraUtilsCommandsTest = ''
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$out/bin/cryptsetup --version
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${optionalString luks.yubikeySupport ''
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$out/bin/ykchalresp -V
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$out/bin/ykinfo -V
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$out/bin/openssl-wrap version
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''}
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'';
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boot.initrd.preLVMCommands = concatStrings (mapAttrsToList openCommand preLVM);
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boot.initrd.postDeviceCommands = concatStrings (mapAttrsToList openCommand postLVM);
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environment.systemPackages = [ pkgs.cryptsetup ];
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};
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}
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