On 07/11/18 22:40, Pascal Hambourg wrote:
Le 12/07/2018 à 05:01, David Christensen a écrit :
On 07/11/18 11:29, Pascal Hambourg wrote:
Le 10/07/2018 à 05:33, David Christensen a écrit :

  In the Debian Installer, I choose 'manual' for 'partitioning method', create a new partition table (MBR), and create three primary partitions:

1   ~1 GiB btrfs mounted at /boot
2   ~2 GiB LUKS (random key) with swap

How do you do that ?
AFAIK, you cannot set a random key with LUKS, only with plain dm-crypt.

Perhaps it is plain dm-crypt, not LUKS.  (I am not familiar with the internals of either, so my understanding is that of a parrot or blind man.)

In the Debian Installer for Stretch:

1.  For "Partitioning method", choose "Manual".

2.  Create partitions, including a partition for swap.

3.  Move the highlight to the swap partition and press Enter to invoke the "Partition settings" pop-up dialog, and configure as follows (note "Encryption key" => "Random key" setting):

         Partition settings:
             Use as                      physical volume for encryption
             Encryption method           Device-mapper (dm-crypt)
             Encryption                  aes
             Key size                    256
             IV algorithm                xts-plain64
             Encryption key              Random key
             Erase data                  yes

Yes, this uses plain dm-crypt, not LUKS. You can see it in the resulting /etc/crypttab (no "luks" option),

crypttab(5) -- yes:

2018-07-12 18:04:20 root@po ~
# grep sda2 /etc/crypttab
sda2_crypt /dev/disk/by-id/ata-INTEL_SSDSC2CW060A3_******************-part2 /dev/urandom cipher=aes-xts-plain64,size=256,swap

2018-07-12 18:07:43 root@po ~
# grep sda3 /etc/crypttab
sda3_crypt      UUID=0152d2e2-4cfb-42c4-a121-6fb832962e47                       
        none            luks

and blkid/file/wipefs do not show any LUKS header on the partition.

blkid(8) -- yes:

2018-07-12 17:54:05 root@po ~
# blkid /dev/sda1
/dev/sda1: LABEL="po_boot" UUID="6ff0dd1d-8d46-454b-bb35-a09afc47145a" UUID_SUB="47a80883-0378-43da-b5e2-0ae9f87e2c95" TYPE="btrfs" PARTUUID="8d34b557-01"

2018-07-12 17:54:22 root@po ~
# blkid /dev/sda2
/dev/sda2: PARTUUID="8d34b557-02"

2018-07-12 17:54:23 root@po ~
# blkid /dev/sda3
/dev/sda3: UUID="0152d2e2-4cfb-42c4-a121-6fb832962e47" TYPE="crypto_LUKS" PARTUUID="8d34b557-03"

file(1) -- no:

2018-07-12 17:55:01 root@po ~
# file /dev/sda1
/dev/sda1: block special (8/1)

2018-07-12 17:55:26 root@po ~
# file /dev/sda2
/dev/sda2: block special (8/2)

2018-07-12 17:55:28 root@po ~
# file /dev/sda3
/dev/sda3: block special (8/3)

wipefs(8) -- not today (!).

Therefore, I should say I set up the second partition on my system drives as follows:

2   ~2 GiB dm-crypt (random key) with swap

Note that this setup is flawed when using a partition on an SCSI-like disk : the installer writes the device name /dev/sdX which is known to be not persistent (that's why UUIDs are used instead when possible). But a plain dm-crypt device has no header and UUID. It would be more reliable to use the PARTUUID= (synthetic on a DOS-partitioned disk) instead.

I have been using /dev/disk/by-id/* successfully for a while, but /dev/disk/by-partuuid sounds even better -- this will prevent confusion if and when I move partitions or images to other devices.

Thank you for the pointers.  :-)


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