Science Interviews


Fri, 6th May 2016

How to hide a top secret message

Professor Mark Lorch, University of Hull

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Scientists have demostrated how to hide a secret message using everyday Top Secretliquids, like cola, wine or coffee. Graihagh Jackson went undercover to meet Mark Lorch to find out more...

Mark - This group in Israel have come up with a way of encoding messages, and hiding messages, and then decoding them with common household liquids, so, it could be a glass of wine, or whatever. And so, that person that you’ve spotted over in that corner may well be that secret agent.

Graihagh - That’s pretty awesome!

Mark - It is, isn’t it. What they’ve done is they’ve taken a load of fluorescent molecules and combined them. Fluorescent molecules are basically molecules that absorb light of one wavelength and then emit it in another wavelength. Now the really cool thing about this molecule then is that the light it gives off is entirely dependent on the conditions it’s in. If it’s in coke, for example, it will give off a spectrum of light that’s unique to the coke and, if you put it in a glass of wine, it will give off another spectrum of light, or a cup of coffee, another spectrum of light, and so on. So, using that, they’ve managed to come up with a way then of encrypting a message…

Graihagh - What I haven’t told you Mark is that I’m actually as secret agent...

Mark - Oh are you!

Graihagh - ...And this interview - it’s all a ruse so you can tell me how to decrypt secret message. So, say I want to send you message and we’re going to make it really simple. I just want to say hello so Hi is the message we’re going to send…

Mark - Just Hi. Okay that’s… So the first thing we have to do is we have to turn the letter in ‘Hi’ into numbers.  So, let’s say we make ‘H’ 1 and we make ‘I’ 2 - okay. Then what we have to do is encrypt that. What we do now is we take some of this molecule and we put it into a solution - okay. This, again, could be your coke, or your wine, or whatever and you then measure the spectrum of light given off by that molecule when it’s in coke, for example. And then you assign part of the spectrum to each of the letters - the ‘H’ and the ‘I’. Let’s say 500 nanometers, we assign that to ‘H’ and 520 nanometers, we assign that to ‘I’, and then we measure the amount of light at 500 nanometers and 520 nanometers, and that gives us a number. So the amount of light given off, we measure that in arbitrary units. Let's say 500 nanometers that corresponds to ‘H’, we get a value of 5, and 520 nanometers which corresponds to ‘I’, we get a value of 10. Now what we do is we add the 5 and the 10 to the 1 and the 2. So 5 plus 1 equals 6 and 10 plus 2 is 12.

Graihagh - So what I’d write down to you is 6 and 12?

Mark - Yes. So you’d send that, however you like. In a letter, in an email in a tweet, whatever, you’d send me 6 and 12. Now, all I have to do is take that same molecule, put in the same solution that you’ve used - the coke again, let’s assume, and measure the spectrum. And then, again, I’ll measure 500 nanometers and 520 nanometers and get the values of 5 and 10 back out, take that off the 5 and the 12 to get 1 and a 2. We already know that the 1 corresponds to ‘H’ and the 2 corresponds to an ‘I’ and, from that, I get my message.

Graihagh - So what I want to know is would spies actually is this or is this just a bit of a gimmick?  Now that we’ve discussed it and everyone knows the secret…

Mark - Well, I did wonder about this because it was published in an open access journal, which makes you wonder…

Graihagh - No longer top secret...

Mark - No longer top secret but, just because you know how the system works, doesn’t mean it isn’t still secure. Nevertheless, I think it seems slightly strange.



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