[java] Creating a file encryption algorithm

The encryption used by caesar: get all the chars in the string and add some number to it.

Say the number is 2:
a->c
b->d

Make sure you start at 0 again when you run out of the range of a char.

(use String.charAt(someIndex) to get the chars and String.length() to get the number of chars)

A more complex encryption can be found here: matrix multiplication and encryption.

In between Koroljov's methods, you could use exclusive or(XOR). If you use a fixed byte, you XOR with each byte to encrypt and then XOR the same value with each encrypted byte to get back the original. The following program illustrates this:


Alternatively you could randomly generate the encryption byte and store it somewhere in the file(at the start) then on decryption you could read it in to decrypt. This byte would just look like another piece of encrypted data, so it would be hard to figure out what the key was by looking at multiple files.

This is probably a little late, but I saw this in my math book the other day and I thought it was kind of cool.
If you creat an invertable matrix, say a 3x3 matrix, and then break your string into even chunks and convert it to ASCII, in this case every 3 chars.
You can then encrypt your string by matrix multiplying your string chunk(vector) to your invertable matrix.
To decode it just multiply your encoded string chunk by the inverse of your invertable matrix.

Like this:

Encoding

Unicode string Encoded string

| 1,-2, 2|
[13, 5, 5] |-1, 1, 3|= [13,-26,21]
| 1,-1,-4|


Decoding
Encoded string Unicode string

|-1,-10,-8|
[13,-26,21] |-1, -6,-5|= [13, 5, 5]
| 0, -1,-1|

(I suck at ascii graphics sorry)

[Edited by - Wrathnut on October 31, 2004 8:48:27 PM]

Quote:

Original post by Koroljov The encryption used by caesar: get all the chars in the string and add some number to it.

Off-topic, but I was reading a book that mentioned Caesar encryption and how it was used to stop Caesar's enemies from reading intercepted messages. It mentioned that today it would be trivial to crack, but back then it was more than sufficient since his enemies were illiterate. :)

u culd try sandorf's cypher