how do people view encrypted pictures like on this wiki page? is there a special program to do it, or did someone decide to do some silly xor just make a point about ECB? im not a graphics person, so if there are programs to view encrypted pictures, what are they?
+1
A:
Encryption works on a stream of bytes. That is, it takes an array of bytes and outputs another array of bytes. Images are also just an array of bytes. We assign the "r" component of the top-left pixel to the first byte, the "g" component to the second byte, the "b" component to the third byte. The "r" component of the pixel next to that is the fourth byte and so on.
So to "encrypt" an image, you just take a byte array of the pixels in the first image, encrypt it (encryption usually doesn't change the number of bytes - apart from padding) and use those encrypted bytes as the pixel data for the second image.
Note that this is different from encrypting an entire image file. Usually an image file has a specific header (e.g. the JPEG header, etc). If you encrypted the whole file then the header would also be included and you wouldn't be able to "display" the image without decrypting the whole thing.
Dean Harding
2010-05-24 00:58:43
That last part is not quite true. Since most of the header contents are well-known or easy to guess, you could construct a header from scratch and join it up with the rest of the image.
caf
2010-05-24 01:19:41
Well, you could possibly reconstruct *some* of the header, but I don't think you could "display" the encrypted image in the same way that encrypted images are being "displayed" on that wiki page.
Dean Harding
2010-05-24 01:37:32