1. Re: Data Encryption
- Posted by Robert B Pilkington <bpilkington at JUNO.COM>
Jun 18, 1998
-
Last edited Jun 19, 1998
On Thu, 18 Jun 1998 23:16:41 -0400 Alan Tu <ATU5713 at COMPUSERVE.COM>
writes:
>>>>>>
>I use integers. If the number overflows (goes beyond 255 or below 0),
>then I bring the number back into range. (A remainder(new_number, 256)
>should do it, but I simply subtract (or add, if it's decrypting) 256
>to
>it to bring it back to it's allowed range.)
><<<<<
>
>Let's suppose we seed a random number generator so that it returns
>these two sequential numbers:
>
>0, 255
>
>Now you have two bytes you want to encrypt:
>
>239, 240
>
>Add =3D to 239, and you get the encrypted byte. 240+255 =3D 495. It
>overflows, so subtract 256. You get 239. So 239 could mean 239 or
>240. =
>
>Is there any way to tell?
Ok, the file would look like this (but in ASCII characters, not values):
Unencrypted:
239, 240
Encrypted:
239, 239
When you decrypt, using the same password, the same set of random numbers
are generated (a call to set_rand(i), with i being a number created after
doing calculations on the password), the opposite happens, the same
numbers are subtracted:
239-0 = 239
240-255 < 0 so add 256 = 240
And now you have the original file:
239, 240
It looks like you were thinking of a substitution type encryption (ie 255
= 34, 38 = 255, 84 = 38, etc). It's not. It's a *REALLY*NEAT* encryption.
:)
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