Re: xorpng

Chris M. Thomasson <chris.m.thomasson.1@gmail.com> wrote:

On 1/5/2025 1:25 AM, Stefan Claas wrote:

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?

 
To make more content as allowed postable on social media, like X.
 

 
Well, posting a png to say, facebook, well... It's probablly going to
turn it into a jpg... This can ruin the embedded ciphertext in the png
image...

ebay seems to recently be converting jpeg's into webp's after one
uploads them, which would also alter the stored bitmap (as webp is
lossy).  Although given the volume of image data they handle, if webp
is even 5% smaller than jpegs, it becomes a huge storage savings for
them.