Re: xorpng

On 05/01/2025 06:17, Rich wrote:

Stefan Claas <pollux@tilde.club> 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.

 Which brings up the question of: why?
 Why go to the trouble to create an encryptor that is specalized for
just encrypting the internal bitmap data within a PNG, leaving the rest
as a PNG file, when a generic "byte stream" encryptor will encrypt the
entire PNG with no extra effort?

Sorry to come late to the party.
I can think of two places where image formats can be useful in cryptography.
Firstly, lossless image formats can be used to steganographically hide small ciphertexts in the low bits without seriously degrading the image.
Secondly, if you want an eyeball on how tangled your bits are, rip off the image's metadata, encrypt the bitmap data, bolt the metadata back on, and visually inspect the resulting image and look for patterns (or, if you used Tux - of course you did - any remnants of penguin).
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
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