Tuesday, May 09, 2017

Steganography with an AI flavour

Security sources say that in the old days, the bad guys used to encrypt their secret files. Bad idea: when the computer was forensically audited, the interesting files came pre-marked.

Nowadays, whole drives are encrypted, but the authorities have the right - under penalty - to make you divulge the decryption keys.

The solution has long been known: hide your secrets in plain sight. Steganography is usually discussed in the context of image tweaking, hiding your message in the least significant bits of pixel intensity or colour codes.

But that's a bit cumbersome.

Here's an alternative. Get an AI to write a plausible text which secretly encodes your message.

I'll illustrate with an example: your secret message, "Stuff here meet where?"

First we put it through some simple substitution code: "Fghss urer zrrg jurer". Then we get the AI to craft a little story .. each word starting with a letter from the coded message.
"Father gave her something strange. Underwhelmed, Rebecca earnestly recalled zapping relatively recent gifts. Justice underscored revenge, executed remotely."
OK, it's got going to walk by itself out of the slush-pile, but embedded in a folder of quotes it wouldn't get a second glance.

Quite challenging for the AI.


My example has a slight issue: the substitution cipher disrupts the letter frequency in English ('e' becomes 'r' for example). A computer analysis could pick up on that.

But it's easily fixed.

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