Pass+keyfile

dm-crypt [email protected] 3 participants 3 messages Dec 1, 2014

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[email protected]

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2014-12-01 03:02 UTC #0 lore raw

Hi there, is this construction secure? Assuming "keyfile" is a file and "/dev/device" is a block device, both made with /dev/urandom.

cryptsetup open --hash=sha512 --cipher=aes-xts-plain64 --type=plain keyfile keyfile_tmp && cat /dev/mapper/keyfile_tmp | \
cryptsetup open --hash=sha512 --cipher=aes-xts-plain64 --type=plain --key-file=- /dev/device cryptodevice && \
cryptsetup close keyfile_tmp && mount /dev/mapper/cryptodevice /media/cryptodevice

The goal is to use pass+keyfile to decrypt storage. I put it in a script and it works as it should at a glance. Are there alternatives or improvements? Stupid errors maybe?

Thanks.

Arno Wagner

2014-12-01 12:50 UTC #1 lore raw

This construction is redundant and does not provide any additional security as compared to passphrase alone, assuming that your passphrase is secure.

If your passphrase is insecure, you should fix that instead.

Arno

Quoted 19 lines · On Mon, Dec 01, 2014 at 03:54:19 CET, [email protected] wrote:

Hi there, is this construction secure? Assuming "keyfile" is a file and "/dev/device" is a block device, both made with /dev/urandom.
cryptsetup open --hash=sha512 --cipher=aes-xts-plain64 --type=plain keyfile keyfile_tmp && cat /dev/mapper/keyfile_tmp | \
cryptsetup open --hash=sha512 --cipher=aes-xts-plain64 --type=plain --key-file=- /dev/device cryptodevice && \
cryptsetup close keyfile_tmp && mount /dev/mapper/cryptodevice /media/cryptodevice
The goal is to use pass+keyfile to decrypt storage. I put it in a script and it works as it should at a glance. Are there alternatives or improvements? Stupid errors maybe?
Thanks.
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Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: [email protected]
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
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Quentin Lefebvre

2014-12-01 13:49 UTC #2 lore raw

Hi,

I guess his point was to build something like a strong authentication with:
(1) something that I *own* (a key, maybe on a USB key),
(2) something that I *know* (a passphrase).

This doesn't look too bad to me.

But maybe it's worth remembering hash algorithms are ignored with key files in plain mode, so that the --hash=sha512 is not effective and actually equivalent to --hash=plain in this case.

Best regards,
Quentin

Quoted 29 lines · Arno Wagner

This construction is redundant and does not provide any additional security as compared to passphrase alone, assuming that your passphrase is secure.
If your passphrase is insecure, you should fix that instead.
Arno
Quoted 15 lines · On Mon, Dec 01, 2014 at 03:54:19 CET, [email protected] wrote:
Hi there, is this construction secure? Assuming "keyfile" is a file and "/dev/device" is a block device, both made with /dev/urandom.
cryptsetup open --hash=sha512 --cipher=aes-xts-plain64 --type=plain keyfile keyfile_tmp && cat /dev/mapper/keyfile_tmp | \
cryptsetup open --hash=sha512 --cipher=aes-xts-plain64 --type=plain --key-file=- /dev/device cryptodevice && \
cryptsetup close keyfile_tmp && mount /dev/mapper/cryptodevice /media/cryptodevice
The goal is to use pass+keyfile to decrypt storage. I put it in a script and it works as it should at a glance. Are there alternatives or improvements? Stupid errors maybe?
Thanks.