On 2015-12-04 04:42, Ismail Kizir wrote:
It looks a lot more like you don't know what your talking about. Human perceptions of 'randomness' do not align with actual mathematical definitions of it. From a mathematical standpoint, 'random' means that given any arbitrary number of previous values, it is impossible to predict what the next value will be.Clemens,You really don't know what you are talking about. Don't you? :) And this is my last mail about the subject. I don't want to keep the list busy. The original, unencrypted "plaintext" file was all zeroes. When I uploaded to blogspot, it appeared all "red" and it still is. And it has not any "red" cyphertext :) http://ismail-kizir.blogspot.com.tr/2015/11/visual-proofs-of-hohha-dynamic-xor.html
An excellent example of something that 'looks random' to a human but really isn't is machine code. To anyone who's never dealt with it, it looks just like a jumble of bytes. To someone who has dealt with it, it's pretty easy to predict certain patterns, and if you know what to lock for, you can even tell to a certain extent what type of processor it's for (for example, machine code for the MSP430 tends to have lots of 0x4303 words in it, because that's the translation of a NO-OP). Try importing an executable file into Gimp or Krita as a raw image, you'll see definite patterning in a couple of places, but most of it will look like static. Similarly, do the same but with an audio import into something like Audacity, you'll get a mix of silence and static with a handful of odd fixed frequency tones mixed in. Both of these seem perfectly random to most people, but they really aren't, they just seem that way because the structure of the data doesn't fit in the context in which it's being viewed.
I've run essentially the same tests that Clemens did, and got the same results, and as such agree with him and Pavel. Given the output, it's trivially possible to infer the input in a given set of cases, and given that, it's not unreasonable to assume that it's possible to directly infer the input in any arbitrary case. Saying that it's a good encryption algorithm because the output looks different than the input is not a valid argument, you have to do a proper analysis of the output, which means more than just encrypting a bitmap and seeing if you can recognize a pattern in the result. The algorithm is of little practical use beyond the type of thing that ROT13 or a Caesar cipher would be used for (IOW, I might consider using it to obfuscate something to annoy someone who's just being nosy, but I would not by any means trust it for anything that I wanted protected from unauthorized access).
On Fri, Dec 4, 2015 at 9:34 AM, Clemens Ladisch <clem...@ladisch.de> wrote:Ismail Kizir wrote:What means "did not look random"?A plaintext consisting of repeated bytes (zero, or other values) eventually makes your algorithm go into a loop, which results in repeated bytes.On the pictures, there is also an example of "full 0"(it appears red, but it is full 0 bmp) example. And it "looks" perfectly random.No, red is _not_ perfectly random. When I see a red picture, I have evidence that the plaintext was zeroes. Regards, Clemens
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