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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: sci.crypt
Subject: Re: xorpng
Date: Sun, 5 Jan 2025 14:33:17 -0800
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On 1/5/2025 2:21 PM, Stefan Claas wrote:
> Chris M. Thomasson wrote:
>> On 1/5/2025 1:24 AM, Stefan Claas wrote:
>>> Chris M. Thomasson wrote:
>>>> On 1/4/2025 4:21 PM, Stefan Claas wrote:
>>>>> Rich wrote:
>>>>>
>>>>>> If instead you mean some kind of "special, PNG aware, encryptor that
>>>>>> only encrypted the bitmap data of a PNG", but left the file as
>>>>>> otherwise a proper PNG image structure, then that is slightly tricky
>>>>>> (and an algorithm that is only useful for PNG's alone).
>>>>>
>>>>> Yes, this is what I mean.
>>>>>
>>>>
>>>> Well, take a good ol' bag o' bytes and turn it into a valid png?
>>>
>>> No, encrypt a .png, so that an encrypted noise image comes out.
>>>
>>
>> Are you talking about encrypting something A. Taking the resulting
>> ciphertext B and creating a new png C out of B. The png C will have B a
>> a visual entity. Now, since C has the ciphertext B in it, we can decrypt
>> that data back into A.
>>
>> Is this what you are doing?
> 
> I am talking about .png image encryption. I got it working for ppm (P6)
> files, so that when you have created with Gimp a ppm (raw) file it will
> then be encrypted with a password and salt and results in a noise image.
> 
> Have you not seen my online folder with the example ... ???
> 

The PPM still needs it proper format to be a, as you say, noise image?

I have worked a lot with PPM's. Keep in mind that storing ciphertext for 
any file, even the original PPM, JPG, ect, can be stored in another PPM 
for sure. So, the resulting PPM will have the payload of any file, 
another PPM, no problem. Then we can look at the payload as an image on 
the screen.