Bacon Code
So far, we have seen various ways to encrypt and decrypt messages using a secret key. There are also methods that protect information security by encoding a message into a form that people do not easily understand without the need of a key; such methods are called encodings. Morse code is one of the most famous examples of encodings. Under the umbrella of encoding methods, there is a branch that hides a message within another message. Such methods are called steganography. This week we will use a steganography method called Bacon code (also known as Bacon cipher), which was invented by Francis Bacon in 1605.
Bacon code encodes an English letter into a string of 'a's and 'b's of length five. The translation is given in the table below.
Note that letters I and J are encoded into the same code, and letters U and V are also encoded into the same code, so there might be some ambiguity when decoding the message. As an example, the word "Gold Coast" is encoded as "aabba abbab ababa aaabb aaaba abbab aaaaa baaab baaba", and the word (a name) "Dijkstra" is encoded as "aaabb abaaa abaaa abaab baaab baaba baaaa aaaaa ".
But Bacon code can go a step further. The encoder and the decoder can negotiate a strategy of representing the 'a's and the 'b's in a message, and many possible strategies can be devised. For example, given a text, we can translate every uppercase letter to an 'a', and translate every lowercase letter to a 'b'. Then we can hide the encoding into a message. Consider the sentence
GrFFITh uNiVeRSITy iS In QUeenSLAnd.
If we map each uppercase letter to an 'a' and map each lowercase letter to a 'b', then the sentence becomes
abaaaab bababaaaab ba ab aabbbaaabb.
Then we group the letters by five, and obtain the following:
abaaa abbab abaaa abbaa baabb baaab b.
The last 'b' is not in the Bacon code, so we can ignore it. Decoding the above using Bacon code, we have the following:
IOINUS
Still seems cryptic? Remember I and J correspond to the same code, so we can try changing I to J to see if we can form an English sentence. Right, it says "JOIN US"!
