Secret Codes: A History of Cryptography (Part 1)

Secret Codes: A History of Cryptography (Part 1)

#Secret #Codes #History #Cryptography #Part

The written word is the most important invention in human history but as long as humans have had the ability to share information they’ve also had the need to conceal that information as well this need led to the invention of cryptography the word cryptography comes from the greek meaning hidden writing

And some of the earliest forms of secret writing come from ancient greece as well herodotus the father of history as he is known described a way of hiding writing by putting a message on a wooden board and then covering it with a layer of wax during greece’s war with persia in the

5th century bc this approach was used to send military correspondents this sort of concealment is known as steganography meaning covered writing it was common all over the ancient world from greece to china but as you can probably guess this approach has some issues the main one being that if the message is

Discovered its contents will be easily revealed this dilemma gave rise to cryptography which doesn’t hide the existence of a message but instead hides its meaning cryptography can be broken down into two subtypes transposition and substitution transposition is when a document is rearranged creating an anagram and it is the earlier form of cryptography

An early historical example is once again from ancient greece specifically the city-state of sparta the spartans used a device called a sky tale to hide their military communications it consisted of a strip of leather wrapped around a wooden rod the sender would write his message on

The leather as it was twirled around the rod like so when unfurled the message would seem like a jumble of letters but once the receiver wrapped the strip around an identical rod of their own the message would become clear transposition has some major flaws though for one a short message has a limited

Number of scramblings for instance the word dog can only be rearranged five ways and larger messages while more difficult to disentangle for an interceptor will also be too difficult for the intended receiver as well because of this cryptography by way of substitution was created substitution rather than rearranging the letters in a message

Instead replaces the letters altogether the most famous substitution cipher is the caesar cipher as the name implies it was used by the roman dictator julius caesar during the golic wars in the 1st century ad the caesar cipher also known as the caesar shift cipher replaces any given letter with the

Letter three spaces down the alphabet this is why it’s called a shift cipher because the cipher alphabet is simply the plain alphabet shifted three spaces like so traditionally caesar favored a shift of three but as you can see you can shift the alphabet as many times as you want

Accordingly there are 25 variations of the caesar cipher this is pretty good but if someone knew you were using a caesar cipher to encrypt your message they could brute force their way through by checking all 25 shifts but if you scramble the alphabet at random instead of simply shifting it over

You get 400 septillion that’s 400 followed by 24 zeros different permutations so obviously a wannabe code breaker would have no chance brute forcing his way through such an encryption however a totally random arrangement of the alphabet would also be difficult for the receiver of a message to remember

One solution to this problem is a keyword cipher essentially the sender and receiver of a secret message would agree on a keyword and that would be used to construct the cipher alphabet let’s say our keyword is shift easy enough to remember right so the cipher alphabet would be made by spelling

Shift then filling in the alphabet according to the last letter of the word in this case t like this throughout the rest of the roman empire’s history and into the 6th century a.d these simple ciphers broadly called mono-alphabetic substitution ciphers were used to great success that is until the 8th century when a

Group of ingenious scholars found a way to break through these puzzles in the middle east about a hundred years after the death of the prophet muhammad a new dynasty took power called the abbasid caliphate this new leadership heralded what is called the islamic golden age this time of prosperity and

Peace was the perfect cradle for an intellectual age islamic scholars centered in the baghdad house of wisdom collected works on astronomy medicine alchemy music mathematics and more they also added their own knowledge to the collections during this time muslim theologians were studying the quran and the hadiths they wanted to know which revelations

Came earlier in the quran and which hadiths were genuine and which were not they did this by using new statistical and linguistic techniques chief among them was called frequency analysis scholars saw how often words were used in the quran and the hadiths and this investigation would show whether the linguistic styles and

Etymological idiosyncrasies of the documents were in line with muhammad’s they also used this analysis on individual letters not just words and in doing so discovered that certain letters were more frequently seen than others the first scholar to realize this frequency analysis could be used to break ciphers was a man named abu yousuf

Yakub uh this guy we’ll just call him al kindy he was a very important philosopher who wrote hundreds of works on all sorts of subjects from mathematics to music to medicine he also wrote a treatise on cryptanalysis the study of code breaking here’s a quote from his book which concisely explains his ingenious

Technique to solve an encrypted message find a different plain text of the same language long enough to fill one sheet or so and then count the occurrences of each letter call the most frequently occurring letter the first the next most occurring the second and so on then look at the ciphertext

And also classify its symbols find the most occurring symbol and change it to the first letter the next most common symbol is changed to the form of the second letter and so on until we account for all the symbols of the cryptogram we want to solve essentially

Find the most occurring letter in a cipher and assume it is the most occurring letter in the normal alphabet in english the most common letter is e followed by t and so on well the least common are q and z here’s a handy chart as you might be able to guess

This method can’t be used unconditionally say you’re deciphering a secret treatise on zebras xylophones and quails you wouldn’t expect to see these letters z x and q very frequently and that would probably throw a wrench in your analysis still an intelligent cryptanalyst can break pretty much any monoalphabetic substitution cipher using frequency analysis

Even when letters don’t line up perfectly with their statistical likelihood heading back west europe have been going through the dark ages while the dark ages is generally a term i dislike when it comes to cryptography it is fitting as medieval europe had little interest in the subject

That was until the renaissance with the outpouring of interest and study in the arts and sciences during this time the study of cryptography was reinvigorated too the political situation in europe was also responsible for the renewed interest in keeping communication secret this was especially true in italy

Which at the time was not a unified country but a mishmash of small kingdoms and city-states all constantly bickering with each other so because of this political intrigue mixed with the leaps forward in scholarship cryptography became a burgeoning industry by the 15th century almost every court in europe had a cipher office

And every ambassador a cipher secretary but with the islamic code breaking techniques having been brought to the west the cryptographers were still at a disadvantage they needed new innovations to trip up the cryptanalysts the first was the introduction of nulls nulls are symbols put into a cipher that have

No meaning let’s say you had a cipher made from numbers 1 to 50. a quick side note you may think that a cipher made from symbols or numbers instead of letters would be more difficult to solve but they’re not frequency analysis works just fine regardless of what images are used

Ciphers using things other than letters existed for centuries before this i just hadn’t mentioned them so a cipher made from 1 to 50. well seeing as there are only 26 letters in the english alphabet only about half of these numbers would actually correspond to letters the rest would be nulls the second

Innovation was to simply misspell the encrypted message so that when a cryptanalyst tried to break the cipher he would slowly uncover misspelled words and then stop thinking he’s going about it all wrong and lastly the introduction of codes in cryptography codes and ciphers are two different things

Codes are words that mean other words like a code name codes replace words while ciphers replace letters codes are obviously most useful when applied to a short message but not so good with long messages because of this limitation cryptographers started using nomenclatures nomenclatures are a mix between ciphers and codes essentially a message

Would be encrypted using a cipher while also using a small list of important code words as impressive as all these new techniques were a cunning and intelligent code breaker could figure out the nulls ignore them as spellings and understand the code words through context for decades cryptanalysts still had the upper hand

As shown in the case of mary queen of scots while imprisoned on trumped-up charges queen mary took part in the babington plot a plan by english catholics to kill queen elizabeth and replace her with mary she had corresponded with the conspirators using a cipher which was unfortunately broken by

English cryptanalysts proving queen mary guilty she was executed on february 8 1587 so clearly cryptographers needed a better system and in the 16th century a frenchman named vigineri would come up with it join us next time as we continue to explore the history of cryptography

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