Lot's of one-time-pads available for $15 each! [was: Nth digit of PI]

[Steven D. Majewski]

On Fri, 16 Jun 2000, Tim Dixon wrote:

> The strongest possible encryption is a secret key one time pad.  A one
> time pad is an encryption method by which each byte (or couple bytes)
> is encrypted using a different key which is discarded and not used
> again. 

> 
> There are two problems:  one is that it's a secret key system and not
> a public key system, so it's not useful for many applications.  It
> doesn't work for something like SSL or PGP, for instance.  This is a
> characteristic of secret key systems.
> 
> The second is the enormous effort involved in producing one time pads.
> You need enough bits in your pad to encrypt the entire message;
> essentially for a 16K message, your key would have to be 16K long as
> well.  Naturally, you need to get the key to the recipient via some
> secure means and communicate what portion of the pad is used by a
> particular message.


Nowadays, Music CDs and DVDs are an easily available source of a stream
of bits. All you have to do is secretly agree upon a disk, and maybe
a starting track or location in the stream. ( There's also an infinite
set of algorithms to agree to run that stream thru. For example: 
break the stream into 3-bit chunks, take a group of 7 chunks and drop
all but the first and last, concatenate them all and rechunk them into
8-bit bytes, and XOR them with the data stream. That's not too complicated
for someone to memorize. ) 


Only problems is that encryption based on a physical artifact is 
vulnerable to physical snooping: someone dressed in black breaks into
your house in the middle of the night and catalogs your CD collection 
( or if you're not too smart, finds the one left sitting next to the
computer! ) Books used to be used as one time pads, and they had the
same vulnerability -- sometimes it was possible, by close inspection, 
to tell where the book had been frequently left open. ( The Bible 
was a popular choice, as there were reasons to make carrying one
around constantly not be considered suspicious behaviour. ) 


--- Steve Majewski  
    Chop wood, carry water.