Task $3-$ Enigma

For this task, you need to implement a simplified version of the famous Enigma cipher that was used by the axis powers in WWII. The cracking of the Enigma cipher was also a seminal moment in the history of computer science. You can learn a bit more about this in the History section on Enigma.

For a detailed explanation of the workings of this cipher, first read our write$-$up in the Enigma Operation for this PA section. This will provide you with all the details you need. Make sure you thoroughly understand the Enigma operation before you go on to the coding part. Note that the Enigma treats spaces just like other characters $($so we are again working with a set of $27$ symbols, as with the substitution cipher$).$ Again, index$\_$of$\_$char$()$ and char$\_$at$\_$index$()$ will be extremely helpful in implementing your code.

The function you need to implement has the following functionality:

cipher$\_$enigma$($arg$1,$ arg$2,$ arg$3,$ arg$4)$

The first argument, arg$1,$ is a string containing the data that needs to be encrypted or decrypted. It is not modified by this function.

The second argument, arg$2,$ is a string that will contain the result of the encryption or decryption.

The third argument, arg$3,$ is a non$-$negative integer number $($of at most $4$ digits$),$ specifying the key of the Enigma cipher. The two rightmost decimal digits $($what are called the least significant digits$)$ of this number represent the initial shift $($to right!$)$ of the inner rotor $($what we called key$\_$part$\_1$ in Enigma Operation for this PA$).$ The next two digits give the initial shift $($to the right$)$ of the middle rotor $($what we called key$\_$part$\_2).$ For example, the number $1329$ means that the initial shift of the inner rotor is $29$ positions $($which is the same as $2$ positions, as it wraps around after $27$ turns$)$ and that of the middle rotor is $13$ positions. So the following keys all result in the same starting positions of the rotors: $1302,1329,9483,$ etc.

For the fourth argument, arg$4,$ which is an integer, we either pass ENCRYPT or DECRYPT, which are the two constants that we defined.

The function returns nothing.

The default positions for all the rotors $($i$.$e$.,$ without any initial shift$)$ and the organization of the symbols on each of the rotors is as shown in Enigma Operation for this PA$.$ This information is also already included in the ciphers.c starter code, so you don$$t have to copy it from this document. When testing your Enigma, make sure it also works for messages longer than $27$ symbols $($to capture the effects of the rotors moving after encrypting each symbol$).$