# Primes With Complex Factors

Lee Brotherston lee at nerds.org.uk
Sun May 11 18:19:01 BST 2008

```On Sun, May 11, 2008 at 01:53:34PM +0100, Frank Mitchell wrote:
> When Gauss discovered Complex Numbers he found he could use them to factorise
> Primes.

I'm no mathematical genius but I thought that by definition primes
cannot be factored, other than by one and themselves.

> For instance 2 can be factorised as (1+i)*(1-i).

Again it's been a while since I've done maths, but that doesn't seem

(1+i)*(1-i) = 2
1-i+i-i^2 = 2
1+i^2 = 2
i^2 = 1
i = sqrt(1)

If i is the squareroot of 1, it's not a whole number and therefore not
a factor.

> Recently this topic seems to have attracted further research, and it seems to
> me this could be connected with Cryptography and its use of enormous Primes.
> Apparently the People's Republic of China are getting expert at cracking

Cryptography relies on factoring a huge semiprime, this means a large
number that can only be factored into two primes.

If there are governments making large advances in cracking
ciphers I would suspect one of three things are taking place:

- New hardware has been sourced to just throw processing power at the
problem.  I seem to recall that the hardware in some HDTVs, and
PS3's can be harnessed for some pretty impressive cracking times due
to the graphics chips, this means that hardware can be aquired at
a reasonable price to create a cracking farm.

- Holes have been discovered in specific ciphers (or implimentations
of ciphers) which enable the shortcutting of the cracking process.

- Memory to processing tradeoff techniques (along the lines of Rainbow
tables) could be used if suitably funded to generate the tables in
the first place.

I could of course be completely wrong, as it's a boiling hot sunday
afternoon, I'm tired and I've not attempted maths for quite some time
:)

Cheers

Lee

--
Lee Brotherston - <lee at nerds.org.uk>

```