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Date: Tue, 05 Apr 2011 06:17:28 +0100
From: Gareth Randall <gareth.randall@...gin.net>
To: oss-security@...ts.openwall.com
Subject: A new way of writing secure data backups, combining RAID and one
time pads.
Hi,
I have published a free software project called "Triplyx", which writes
data to a set of three storage devices in such a way that if any one of
them is lost or stolen, it cannot be used to recover the data. Any two
storage devices can be brought together to recover the data. It was
created for use with offsite data backups.
The concept is simple, although I have never seen it done in a
commercial or open source product.
Triplyx writes three copies of the data input D to separate storage
devices. Each copy is exclusive-OR encrypted with a random "one time
pad", and one of the other one time pads is written alongside it in the
same "volume" (file). In my code, the output can be any file or a Unix
device.
In the following example, the one time pad (random) data streams are A,
B and C.
D^A means that each byte of D is XOR'd with the corresponding byte of A.
Volume 1 contains: D^A and B
Volume 2 contains: D^B and C
Volume 3 contains: D^C and A
So, for example, storing a 100kbyte file (D) would result in the
following being written to the volumes:
Volume 1: 100k of D^A, along with 100k of B.
Volume 2: 100k of D^B, along with 100k of C.
Volume 3: 100k of D^C, along with 100k of A.
Note: The D^A and B streams are actually "striped" so that they can both
be read and written at the same time without needing to keep copies of
large amounts of data. This is designed especially to support tape as a
backup medium.
Restoring the data simply requires any two volumes. So, for example,
volumes 2 and 3 contain C and D^C, allowing the original D to be
reconstructed.
See:
http://www.triplyx.com/
https://sourceforge.net/projects/triplyx/
I've also written a paper describing it.
URL of the paper is:
http://sourceforge.net/projects/triplyx/files/Triplyx/doc/A%20Backup%20Method%20Providing%20Media%20Redundancy%20and%20One%20Time%20Pad%20Encryption%20v1.1.pdf
The paper also documents a similar method which allows more data to be
stored but with some implications for security. That is, write the data
three times, encrypted with different symmetric keys, and then store the
other two keys not used for the current data on each storage medium.
I.e.
Volume 1: (D enc with J), K, L
Volume 2: (D enc with K), J, L
Volume 3: (D enc with L), J, K
where J, K and L are encryption keys.
This allows more data to be stored because it does not need to store an
entire one time pad, but contains risks of attacks on either the
encryption algorithm or the means of choosing the keys.
Coming from an "enterprise" point of view, offsite backups could now be
stored for long periods of time without having to worry about encryption
passwords being lost due to staff turnover. Also, compliance with data
protection legislation should be easier to demonstrate.
For the one time pad method, if the random number generator is good
enough then a single lost backup device can never result in exposure of
confidential data.
Yours,
--
======= Gareth Randall =======
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