Destroying data down to the 13th level??? Post: 18937

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Special Forums Hardware Filesystems, Disks and Memory Destroying data down to the 13th level??? Post 18937 by Perderabo on Thursday 4th of April 2002 10:20:52 AM

04-04-2002

Administrator Emeritus

Hmmm...well I had not heard of /dev/random either... I see that SunOS has a /dev/random and a /dev/urandom symlink to it. I didn't find anything with man -k. I'll look around for some docs on this thing.

As for just writing zeroes once, yeah it's probably good enough if you don't have physical access to the disk. But to take a disk with sensitive data, write zeroes to it and then make it available to the web would give a security guy a heart attack.

Suppose a write operation failed because the disk is flakey? A good driver will detect that and arrange for the write to return -1. But bad drivers exist. And few programmers do a good job of checking return codes anyway. Later on, someone might get the data with a lucky read. And this line of "reasoning" applies equally to a disk that has been wiped a thousand times. Security guys think this way...

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LEARN ABOUT V7

rk

RK(4)							     Kernel Interfaces Manual							     RK(4)

NAME

       rk  -  RK-11/RK03 or RK05 disk

DESCRIPTION

       Rk?   refers  to an entire disk as a single sequentially-addressed file.  Its 256-word blocks are numbered 0 to 4871.  Minor device numbers
       are drive numbers on one controller.

       The rk files discussed above access the disk via the system's normal buffering mechanism and may be read  and  written  without	regard	to
       physical  disk  records.   There  is  also a `raw' interface which provides for direct transmission between the disk and the user's read or
       write buffer.  A single read or write call results in exactly one I/O operation and therefore raw I/O is considerably more  efficient  when
       many  words  are transmitted.  The names of the raw RK files begin with rrk and end with a number which selects the same disk as the corre-
       sponding rk file.

       In raw I/O the buffer must begin on a word boundary, and counts should be a multiple of 512 bytes (a  disk  block).   Likewise  seek  calls
       should specify a multiple of 512 bytes.

FILES

       /dev/rk?, /dev/rrk?

BUGS

       In  raw	I/O  read  and	write(2) truncate file offsets to 512-byte block boundaries, and write scribbles on the tail of incomplete blocks.
       Thus, in programs that are likely to access raw devices, read, write and lseek(2) should always deal in 512-byte multiples.

																	     RK(4)