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n Sir Francis Bacon was an extremely importantnpolitician at the court of King James I, and thus was no stranger to intrigue.nIn the course of his day job, he was necessarily involved in the world ofnespionage and spies and which, unless you’ve been involved in it, you’d imaginenbeing all cool and so forth but if you have been involved in that world thennyou will know it to be dull, boring and mind-numbingly tedious. Bacon knew anlot about codes, ciphers and cryptography; he wrote quite a bit about them in hisnnumerous works. Book Six of The Advancement of Learning is wherenhe explains the system of cryptography that is called a bi-literal cipher.
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| Francis Bacon – Frontispiece – Novum Organum |
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nItnworks like this. At its heart, it’s a substitution cipher, which means that onenthing stands for something else. The simplest sort of this sort of cipher isnwhen a single letter stands for another letter; this is called a CaesarnCipher or a shift cipher. For instance, let’s say we substitute eachnletter of the alphabet with the letter that follows it in the alphabet – so thenword ‘cat’ would be rendered as ‘dbu’, or ‘dog’ would benrendered as ‘eph’.
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nBacon starts by taking this a step further, wherebynfive letters are substituted a single one. The letter ‘a’ becomes ‘aaaaa’. Thenletter ‘b’ becomes ‘aaaab’. The letter ‘c’ is ‘aaaba’. The whole of thenalphabet is rendered thus, down to ‘z’ as ‘babbb’. You can see the full alphabet in this illustration.
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| Francis Bacon – Bi-Literal Cipher |
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nSo far, songood. The next step is to take the five letter substitutions for the letters ofnthe message you wish to encrypt. Let’s say, for example, we need to send thenwarning ‘Fly’ to an agent. We take the three five-letter sets for thenindividual letters of our message – the letter ‘f’ is ‘aabab’, the letter ‘l’nis ‘ababa’ and the letter ‘y’ is ‘babba’. So, we now have ‘aabab ababa babba’.
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| Francis Bacon – De Augmentis – Book 6 – Bi-Literal Cipher |
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nWe now need a seemingly innocent phrase that will not arouse suspicion. Itndoesn’t what this is, providing it contains at least the same number of lettersnas our little coded substitution (in this case, at least fifteen letters). Let’snuse the phrase ‘Stay where you are’, (which just happens to have fifteennletters in it). Now take the coded letters and write the phrase beneath it,nthus:
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n aabab ababan babban
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nstayw hereyn ouaren
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nand then, wherever there is a letter ‘a’ write annormal, roman letter but where there is letter ‘b’, write an italic letterninstead. This gives us:
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naabab ababan babba
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nstayw herey ouare
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nAnd there you have your encrypted message, when younmove the letters back into their proper order. It now reads:nn
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nStay wherenyou are.
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nNow, to decode it, our hypothetical agent splits ournmessage into groups of five letters, and for each ‘normal’ letter he writes ann‘a’ and for each italic letter, he writes a ‘b’, and then looks at his alphabetnand matches the relevant block of five ‘a’s or ‘b’s with its correspondingnletter, thus giving him the letters of the true message, and he takes thenappropriate action (we hope).
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nIn the above example, to make the difference anlittle easier to see, I’ve used bold and italic letters. But to send a lessnconspicuous message, it would be better to use two distinct fonts – let’s callnthem font-a and font-b. The letterforms are similar enough not to arousensuspicion but different enough to allow them to be used in the code.
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| Example of a Bi-Literal Alphabet |
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nYou cannsee in the illustration, for example, that the two capital letter ‘A’s arensimilar, but the font-a capital letter is a little plainer than the font-bncapital, which has a flourish at the top and slightly curlier serifs at thenbottom. It is the same with each letter; each is just that tiny bit differentnin the font-a and font-b examples. Bacon uses the following example to make hisncipher clear. He takes a message sent from a Spartan general that reads,
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n“Perditaenres. Mindarus cecidit. Milites Esuriunt. Neque hinc nos extricare, neque hicndiutius manere possumus.” (It means, basically, that All is lost, Mindarus is killed, the soldiers are hungry and we can neither escape nor remain here).n
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nThen, taking the words one by one, letter by letter, they are coded into theirnfive letter counterparts. So, in the first word, ‘Perditae’, P = abbba, E =naabaa, R = baaaa, D = aaabb, I = abaaa, T = baaba, A = aaaaa and E = aabaa.nThis is done for each of the words.
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nWhen this is done, Bacon selects anotherntext that will serve as the innocent message that will convey the code. Henchose one of Cicero’s Epistles that begins, “Ego omni officio.” Whereneach letter in his coded message corresponds to an ‘a’, this is set usingnfont-a. Where there is a ‘b’, then font-b is used – so for the first letter ofn‘Perditae’, the letter P, which is encoded as abbba, he uses font-a, font-b,nfont-b, font-b, font-a. Slowly, the whole message is encoded using the twondifferent fonts. The result can be seen in this illustration.
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| Bacon’s Coded message using his Bi-Literal Cipher in an Epistle of Cicero |
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nWhen the messagenis received, the agent disregards what the text says on its face-value. Hensimply divides the text up into blocks of five letters. So, ego omni officionbecomes egoom/nioff/icio[a], and then the font-a letters are written as ‘a’ andnfont-b letters are written as ‘b’. This gives abbba aabaa baaaa – the PER atnthe beginning of Perditae. And so on and so on until the whole of thenmessage is revealed.
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nIt is an elegant system of coding if a little outdated andnimpractical in today’s world, where different fonts are far too conspicuous innemails and other electronic texts. However, the nuts and bolts of Bacon’snbi-literal system work on the difference inherent in a binary system, which isnideal for use in the on/off binary world of computers. (Remember, there are 10nkinds of people in this world – those that understand binary notation and thosenthat don’t).
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