Re: Fast Encryption

"Jonathan Wood" <>
Sat, 7 Feb 2009 09:46:31 -0700
"David Ching" <> wrote in message

When I started using encryption for my shareware protection, I was struck
by how many partially documented solutions there are. It's hard to know
which is best for your application, especially when your needs are
changing, e.g. will I store passwords or won't I? The article you
referenced is based on RC4, a popular though aging stream cipher.
Ironically, wikipedia said it's known for its speed, so how fast does your
stuff need to be? ;)

Yeah, I played with it quite a bit last night and it got faster. My concern
is that I was going to allow larger blocks of data and still be fast. But
there's probably no way to encrypt 4MB without there being a bit of a delay.

If only casual encryption is required, you won't find much faster than a
simple XOR algorithm. Simply XOR each byte of your content with a fixed
or varying byte and save the result. When you read it back, XOR each byte
with the same value you used the first time on that byte. This works
because XORing a byte with the same value twice leads to the original
value. XOR is something that computers natively know how to do; the
transistor gates in the hardware are built up from XOR basic building
blocks. Perhaps you could start with XOR and delay further study until it
is readily apparent that you need better encryption.

Actually, the algorithm I'm using also uses the same process to encrypt as
it does to encrypt, just like XOR.

The idea of the program definitely includes the ability to store private
information. So XOR might not be enough. Although it might be interesting to
see how much faster it is than what I have now.


Jonathan Wood
SoftCircuits Programming

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