Safe to print sensitive data in Win 7/8, or does it cache plaintext to disk?

1

I dual boot Linux/Windows 8. In Linux, where I usually work, /home is encrypted, /swap is encrypted, and sensitive files are redundantly encrypted on top of that.

Printing, however, doesn't work on the Linux side, so I need to boot to Win 8 to do that. Win 8 can't see the encrypted files, so I need to decrypt them to some temporary location before printing.

Even if I put the decrypted files on an external drive (on which I will use srm or similar forensic-level-delete tools), I'm concerned that Windows will, at some point in the printing process, write the unencrypted data to the unencrypted Win 8 NTFS partition somewhere, making it theoretically recoverable by someone.

Anyone have any insight on if I should be concerned? If so, how to get this done securely?

user272901

Posted 2013-11-10T08:03:27.367

Reputation: 13

I'm wondering what's so sensitive it needs to be encrypted point to point, yet be printed out on paper – Journeyman Geek – 2013-11-10T09:51:44.600

Admittedly rare, but e.g. printing out online account details for non-technical relatives to have as a backup of in case of death, etc. Obviously a security risk to print it out, yes. But I'd be more comfortable with a printout in a safe than data lying around a windows install. – user272901 – 2013-11-10T22:06:19.977

Answers

1

No, it is not safe unless you have the Windows system disk encrypted and unless you use pre-boot authentication.

The Windows Print Spooler stores the print jobs into temporary files at multiple places. See for example

You have several options:

  • Make the printing working in your Linux. (not sure if possible)
  • Install the Windows into an encrypted virtual machine. Then you will even be able to configure Linux to print using the Windows as a print server.
  • Encrypt the Windows installation system disk and use pre-boot authentication.
  • After every printing safely delete all temporary files and wipe the unused disk sectors. This would be the worst method - the slowest one and least trustworthy.

BTW when transferring files between systems why do not you use a multi-platform encryptor like TrueCrypt? From Linux you can mount the Windows partition and have the TrueCrypt container there.

pabouk

Posted 2013-11-10T08:03:27.367

Reputation: 5 358

Also be aware of that some printers internally store print jobs to a harddrive. Besides that many printers secretly print steganographic watermarks so your sensitive printed data could possibly be identified with your printer and print time.

– pabouk – 2013-11-10T11:08:03.097

Great answer, thanks. I'm going with a VM (which itself is in an ecrypted directory). – user272901 – 2013-11-10T22:06:51.947

re: TrueCrypt et al. -- nice to know it's there, thanks, but I don't even want access in Windows if it's going to leave insecure copies lying around. (For general file sharing, i have plenty of unencrypted shared partitions.)

Just for the record, I infer from your answer that Linux is trustable not to spool unencrypted versions when printing files (assuming /home is encrypted)? – user272901 – 2013-11-10T22:08:45.687

I do believe you can do FDE on windows with truecrypt – Journeyman Geek – 2013-11-10T23:17:58.623

@user272901: I am sorry, I did not evaluate security of the Linux machine. The printing system (CUPS) and the components the system uses will create temporary files containing unencrypted information at least in /var/spool/cups*/ and /tmp/. Certainly if you are concerned about security you should encrypt the complete drive (not just some directories). In some Linux distributions (i.e. Ubuntu) you just select the option during installation. Other major distributions have multiple tutorials on the Internet. – pabouk – 2013-11-11T07:20:34.930

Asked: 2013-11-10T08:03:27.367

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Active: 2013-11-10T09:36:36.937