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[memo]

Image obfuscation (encryption method)

[thebruce]

I like the latter extended version... altering the LSB (least significant bit) of each pixel in an image is a common (& simple) steganography process... but having the key image provide the bits in each pixel in which each message bit is encoded is nice application of a vigenere-style encryption to an image...

The next trick for a puzzle would be figuring out where that key image (grey scale noise, effectively) could be hidden/encoded for retrieval.

If obfuscation of the entire puzzle imagery isn't an issue, you could provide one image with an alpha channel. Take the original image, apply the random 0-7 bit steganography, then hide key noisy image as the alpha channel. The resulting image would be somewhat visibly noisy, and randomly transparent But all the puzzler has to go on is a lot of bitty noise (at least until the reason for the noisy alpha channel is determined)... (or until they find this thread )

Steganography is a very neat and flexible thing!

[memo]

@thebruce;

Yes, the "carrier" image does best with a lot of high-frequency semi-coherent noise. I like pictures of trees, myself... but really, anything that avoids large blocky patterns is a good start.

As far as randomization is concerned, you could even go so far as to encode binary changes into the RGB channels of an image. Since the pixel intensities aren't necessarily shifted as much as the color balance, it makes detection that much harder.

So if my PNG file is 100 x 100 x 3 @ 8bit resolution, and I choose... say... the 3 least-significant bits to encode my message? Then we get (100 * 100 * 3) ^ 3 permutations. If a text recognition algorithm can complete within 1ms, you'd still be looking at around 1000 years as an upper-bound for search times.

Since the cipher image would also live in 8-bit integers, you could theoretically use text as a means to encode the cipher. Y'know. When you're not making tinfoil hats, because at that point, you'd need 'em.

[thebruce]

Aye, I've made a 4 channel puzzle before =) with 8bit RGBA, technically you have 8 bits per channel per pixel for the dimensions of the image. That's 32 bit planes of data. That's potentially an enormous area to encrypt data (which as an image would ultimately just appear to be noise).