Hosed encrypted drive. Is disaster recovery possible?

My question, as you might guess - is there any possibility of recovering the vast amount of data still on the drive? I could do it with an unencrypted disk, but I have no idea how to proceed in this case.

Evening all,

I'm not very hopeful of a positive response, but having just made my worst mistake in thirty years of computing I thought this would be where most of the relevant knowledge is.

I have an external 1.5TB Seagate drive, encrypted with dm-crypt/luks and formatted xfs.

In a state of dog-tiredness, thinking I was pointing at a USB stick, I have inadvertently wiped a few hundred MB of the beginning of this disk with:

   dd if=./archlinux-2010.05-netinstall-i686.iso of=/dev/sdc

My question, as you might guess - is there any possibility of recovering the vast amount of data still on the drive? I could do it with an unencrypted disk, but I have no idea how to proceed in this case.

Thanks for any suggestions. (I've managed not to cry so far...)

Willie

Quoted 15 lines · Willie

Evening all,

I'm not very hopeful of a positive response, but having just made my worst mistake in thirty years of computing I thought this would be where most of the relevant knowledge is.

I have an external 1.5TB Seagate drive, encrypted with dm-crypt/luks and formatted xfs.

In a state of dog-tiredness, thinking I was pointing at a USB stick, I have inadvertently wiped a few hundred MB of the beginning of this disk with:

   dd if=./archlinux-2010.05-netinstall-i686.iso of=/dev/sdc

Quoted 7 lines

My question, as you might guess - is there any possibility of recovering the vast amount of data still on the drive? I could do it with an unencrypted disk, but I have no idea how to proceed in this case.

Thanks for any suggestions. (I've managed not to cry so far...)

Willie

Hi Willie,

sorry, but you will have wiped the salt in the header, which makes recovery impossible. You will also have wiped all keys (they take about the first 8.5MB), which again does make recovery impossible. In fact, any recovery from this would mean that LUKS is badly broken security-wise.

The only protection against this type of error is (besides a conventional backup), a header backup, see the FAQ at
http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions

I did something similar recently, (tired and thinking I was blanking an USB stick), fortunately I had a backup of the whole disk. But the lession to me was: Hands away from dd and family when tired.

Arno

Oh well. Some you lose. Chin up. Onward and upward, etc etc...

Quoted 2 lines · Willie

Oh well. Some you lose. Chin up. Onward and upward, etc etc...

That's the spirit. Only those doing nothing of importance do not screw up sometimes.

Arno

Quoted 10 lines · Arno Wagner

Quoted 2 lines · Willie

Oh well. Some you lose. Chin up. Onward and upward, etc etc...

That's the spirit. Only those doing nothing of importance do not screw up sometimes.

Arno

Well, it's kind of strange. I aborted the dd as soon as I became aware of my moment of crass stupidity and I can still see part of the directory structure, with quite a few file names in there showing proper file sizes, but these seem to be empty of data.

I still have "/dev/mapper/udisks-luks-uuid-c1a534b4-d1ba-40d0-adb8-6d2490f06ade-uid9330 on /media/Seagate_1.5 type xfs (rw,nosuid,nodev,uhelper=udisks)", and obviously I have the pass phrase.

I suppose it's the key that's gone, and there's the kicker, right?

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I still have "/dev/mapper/udisks-luks-uuid-c1a534b4-d1ba-40d0-adb8-6d2490f06ade-uid9330 on /media/Seagate_1.5 type xfs (rw,nosuid,nodev,uhelper=udisks)", and obviously I have the pass phrase.

If you have live mapping still, you are not lost completely yet. Do not reboot! First run "dmsetup table --showkeys" and "dmsetup info -c" and store the full mapping to some file.

If you see dm-crypt mapping there mapped to proper drive, you can still recreate LUKS header with some some magic.

Quoted 2 lines · Milan Broz

If you see dm-crypt mapping there mapped to proper drive, you can still recreate LUKS header with some some magic.

Well, here is the idea how to reconstruct LUKS header from active mapping if header is lost but mapping is still active.
(Note: if device is not active, recovery is impossible).

- it will change LUKS UUID!
- no passphrase needed, it asks for new one (root access required of course)
- cryptsetup 1.1.x required.

Do not save master key file (second param) to unencrypted filesystem!

I'll add something similar to cryptsetup distro into DOC install, for now take this as an idea - see attached script (it will not touch device,
only saves master key to file and print required parameters for cryptsetup).

BEWARE: NO GUARANTEES AT ALL. NOT PROPERLY TESTED.

Example:
If you have mapped device named "luks_sdb", script will produce this:

# <script> luks_sdb /mnt/safedisk/sdb_master_key

Generating master key to file /mnt/safedisk/sdb_master_key. You can now try to reformat LUKS device using:
cryptsetup luksFormat -c aes-cbc-essiv:sha256 -s 256 --align-payload=2056 --master-key-file=/mnt/safedisk/sdb_master_key /dev/sdb

Milan

[---cut here---]
#!/bin/bash

# Try to get LUKS info and master key from active mapping and prepare parameters for cryptsetup"
# (C) 2010 Milan Broz <[email protected]>

fail() { echo -e $1 ; exit 1 ; }
field() { echo $(dmsetup table --target crypt --showkeys $DEVICE | cut -d' ' -f$1) ; }
field_cryptsetup() { echo $(cryptsetup status $DEVICE | grep $1 | sed "s/.*$1:\s*//;s/\ .*//") ; }

which xxd >/dev/null || fail "You need xxd (part of vim package) installed to convert key."

[ -z "$2" ] && fail "LUKS header from active mapping, use:\n $0 crypt_mapped_device mk_file_name";

DEVICE=$1
MK_FILE=$2

[ -z "$(field 4)" ] && fail "Mapping $1 not active or it is not crypt target."

CIPHER=$(field_cryptsetup cipher)
OFFSET=$(field_cryptsetup offset)
REAL_DEVICE=$(field_cryptsetup device)
KEY_SIZE=$(field_cryptsetup keysize)
KEY=$(field 5)

[ -z "$CIPHER" -o -z "$OFFSET" -o "$OFFSET" -le 383 -o -z "$KEY" ] && fail "Incompatible device, sorry."

echo "Generating master key to file $MK_FILE."
echo -E -n $KEY| xxd -r -p >$MK_FILE

echo "You can now try to reformat LUKS device using:" echo " cryptsetup luksFormat -c $CIPHER -s $KEY_SIZE --align-payload=$OFFSET --master-key-file=$MK_FILE $REAL_DEVICE"

Quoted 2 lines · Milan Broz

If you see dm-crypt mapping there mapped to proper drive, you can still recreate LUKS header with some some magic.

Well, here is the idea how to reconstruct LUKS header from active mapping if header is lost but mapping is still active.
(Note: if device is not active, recovery is impossible).

- it will change LUKS UUID!
- no passphrase needed, it asks for new one (root access required of course)
- cryptsetup 1.1.x required.

Do not save master key file (second param) to unencrypted filesystem!

I'll add something similar to cryptsetup distro into DOC install, for now take this as an idea - see attached script (it will not touch device, only saves master key to file and print required parameters for cryptsetup).

BEWARE: NO GUARANTEES AT ALL. NOT PROPERLY TESTED.

Example:
If you have mapped device named "luks_sdb", script will produce this:

# <script> luks_sdb /mnt/safedisk/sdb_master_key

Generating master key to file /mnt/safedisk/sdb_master_key.
You can now try to reformat LUKS device using:
cryptsetup luksFormat -c aes-cbc-essiv:sha256 -s 256 --align-payload=2056 --master-key-file=/mnt/safedisk/sdb_master_key /dev/sdb

Milan

[---cut here---]
#!/bin/bash

# Try to get LUKS info and master key from active mapping and prepare parameters for cryptsetup" # (C) 2010 Milan Broz <[email protected]>

fail() { echo -e $1 ; exit 1 ; }
field() { echo $(dmsetup table --target crypt --showkeys $DEVICE | cut -d' ' -f$1) ; } field_cryptsetup() { echo $(cryptsetup status $DEVICE | grep $1 | sed "s/.*$1:\s*//;s/\ .*//") ; }

which xxd >/dev/null || fail "You need xxd (part of vim package) installed to convert key."

[ -z "$2" ] && fail "LUKS header from active mapping, use:\n $0 crypt_mapped_device mk_file_name";

DEVICE=$1
MK_FILE=$2

[ -z "$(field 4)" ] && fail "Mapping $1 not active or it is not crypt target."

CIPHER=$(field_cryptsetup cipher)
OFFSET=$(field_cryptsetup offset)
REAL_DEVICE=$(field_cryptsetup device)
KEY_SIZE=$(field_cryptsetup keysize)
KEY=$(field 5)

[ -z "$CIPHER" -o -z "$OFFSET" -o "$OFFSET" -le 383 -o -z "$KEY" ] && fail "Incompatible device, sorry."

echo "Generating master key to file $MK_FILE."
echo -E -n $KEY| xxd -r -p >$MK_FILE

echo "You can now try to reformat LUKS device using:"
echo " cryptsetup luksFormat -c $CIPHER -s $KEY_SIZE --align-payload=$OFFSET --master-key-file=$MK_FILE $REAL_DEVICE"

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