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What be a “Cipher”?

Have ye ever had a hankerin’ to write a secret message to a mate, so no other scoundrel can understand it? Then ye need a Cipher, or cipher in the English tongue! A cipher be simply a method that turns plain text into “code” by swappin’ characters (often letters) with other characters. The result looks like gibberish to those who don’t know how the code works. The point be that only those who know the key (the rule for swappin’ the letters) can make the code understandable again. In other words: ciphers make secret messages possible, be it childhood games with secret languages or true spies sendin’ encrypted messages. 😄

There be many a cipher – some use numbers, some use symbols, and modern data encryption uses right complicated algorithms. These complicated algorithms require right complicated maths, so we can be lookin’ at some simpler algorithms first!

Monoalphabetic Ciphers

Let us first examine some o’ the simplest (and oldest) code methods t’ be found: monoalphabetic ciphers.

Monoalphabetic sounds like a fearsome word, aye, but we can break it down: mono means “one”, and alphabetic be about the alphabet itself.

So, monoalphabetic ciphers be codes where ye use a single “encryption alphabet” for the whole message. That is t’ say, each letter in the original text always be swapped with the same letter throughout the encrypted message.

For example, if ye’ve decided that A shall be swapped with X, then all the A’s in the text be turned int’ X.

Caesar Cipher

The classic example o’ a monoalphabetic cipher be the Caesar cipher (named after Julius Caesar, aye). ‘Tis basically a rule t’ “shift” all the letters a certain number o’ places along the alphabet. ‘Tis said Caesar himself used a shift o’ 3 letters in his secret messages. It works such that A becomes D, B becomes E, C becomes F, and so on through the alphabet. (When ye pass Z, ye start back at A again.) A message like ABC would thus become DEF if we use Caesar’s method.

How the Caesar Cipher Works in Practice:

• Choose a key: Decide on a secret number (for example 3) that indicates how many places ye shall shift each letter.
• Replace each letter: For each letter in the original message, find the letter that lies so many places after it in the alphabet (for key 3, A becomes D, B becomes E, etc. – remember to wrap around to A again after Z if needed). Ye can also include Æ, Ø and Å, but this be a bit more complicated.
• Encrypted message: Replace the letters and write the new message with the “shifted” letters. Shiver me timbers – ye have an unreadable, secret text that only those with the key can understand!
• To decrypt (that is, to turn it back into readable text) one simply does the opposite shift back. If ye know the key (e.g. 3), it be as easy to read the message by moving the letters 3 back in the alphabet.

Single-alphabet ciphers be a wondrous way t’ learn the principle o’ encryption, aye. They be simple an’ show how we can use a single rule (a key, ye see) t’ turn a plain text inta somethin’ mysterious an’ unreadable – an’ back again! So next time ye wish t’ send a mate a secret message, ye can use the Caesar cipher! Perchance ye can create yer own variant o’ Caesar’s secret alphabet? 🔐✨

Tasks

Oppgave 1: Datainnsamling

For å komme i gang, må vi samle inn data om de forskjellige skipstypene. Dette inkluderer informasjon som lengde, bredde, dypgang, tonnasje og antall besetningsmedlemmer. Dataene skal samles inn fra offentlige kilder, som skipsregisteret og maritime databaser.

Task 1: Gatherin’ Booty (Data, that is!)

To get us started, we must gather data on the different ship types. This includes information such as length, width, draft, tonnage, and the number o’ crew. The data shall be gathered from public sources, like the ship registry and maritime databases.

Oppgave 2: Analyse av data

Når dataene er samlet inn, skal de analyseres for å finne mønstre og trender. Vi skal se på sammenhengen mellom skipstype og ytelse, samt faktorer som påvirker drivstofforbruket. Resultatene skal presenteres i form av grafer og tabeller.

Task 2: Analyzin’ the Spoils

Once the data be gathered, it shall be analyzed to find patterns and trends. We’ll be lookin’ at the connection between ship type and performance, as well as factors that affect fuel consumption. The results shall be presented in the form o’ charts and tables.

Oppgave 3: Utvikling av modell

Basert på analysen, skal vi utvikle en modell som kan forutsi ytelsen til et skip basert på dets egenskaper. Modellen skal ta hensyn til faktorer som skipets form, størrelse, vekt og motorkraft.

Task 3: Craftin’ a Model

Based on the analysis, we shall craft a model that can predict the performance o’ a ship based on its properties. The model shall take into account factors like the ship’s shape, size, weight, and engine power.

Task 1.1 - Caesar Cipher Encryption

Now we be writin’ some code, aye! We shall start simple by craftin’ the encryption, based on the theory it should be quite straightforward.

Implement encryption with the Caesar Cipher by usin’ a function that takes in text and a number that be the “key”, that is how much the alphabet shall be rotated with.

def caesar_cipher(text, shift):
    result = ""
    for char in text:
        if char.isalpha():
        # find the startin' point based on big and small letters
        start = ord('A') if char.isupper() else ord('a')
        # The tricky shiftin' math
        result += chr((ord(char) - start + shift) % 26 + start)
    else:
        result += char
    return result

Task 1.2 - Caesar Cipher Decryption

Decryption be just doin’ the opposite reckonin’ to encryption, aye. Ye subtract the offset instead o’ addin’ it.

def caesar_decrypt(text, shift):
    return caesar_cipher(text, 26 - shift)

Other Monoalphabetic Ciphers (ex. Atbash)

There be other monoalphabetic ciphers as well! One o’ the simpler ones be called the “Atbash” Cipher.

How Does Atbash Work?

This be a simple one, instead o’ a rotation, letters be mapped to the opposite alphabet. Here be a table showin’ the mappin’:

Task 1.3 - Atbash Cipher Encryption and Decryption

The beauty o’ the Atbash be that, seein’ as how the encryption be a one-to-one transformation, it works directly in reverse. Aye, if ye be havin’ crafted the encryption, ye’ve also, automatically crafted the decryption.

How can this be done in practice?

Ye can either subtract the letter in relation to Z, or create a “Look-up” table. Aye, that means a table or dictionary that contains all the letters from a to z and what they shall become. This can be a good solution if ye wish to create another type o’ encryption.

letters = {
    'a': 'z'
    'b': 'y'
    'c': 'x'
    'd': 'w'
    # ... add the rest o' the letters down below
}

Aye, with this here table ye can go through letter by letter, then fetch the value per letter from the lookup table, and write it out. What must ye do for capital and small letters, savvy?

Part 2 - Cryptoanalysis o’ Monoalphabetic Ciphers

In this here part, ye shall try to craft an algorithm to “crack” a Caesar cipher, that be takin’ a encrypted text, then gettin’ the original text without knowin’ the key.

This can be done somewhat manually, or ye can try to employ simple “cryptanalysis”. This be a concept we shall delve deeper into later, but for now we shall only look at one o’ the simplest ways: Frequency Analysis. Ye can read more about this concept here: Frequency Analysis or here Wikipedia - frequency analysis.

This method can be used in more than just Caesar ciphers, it can be used in more complicated algorithms as well, but Caesar ciphers be so simple that frequency analysis be trivial.

In cryptanalysis, frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers.

Frequency analysis is based on the fact that, in any given stretch of written language, certain letters and combinations of letters occur with varying frequencies. Moreover, there is a characteristic distribution of letters that is roughly the same for almost all samples of that language. For instance, given a section of English language, E, T, A and O are the most common, while Z, Q, X and J are rare. Likewise, TH, ER, ON, and AN are the most common pairs of letters termed bigrams or digraphs), and SS, EE, TT, and FF are the most common repeats. The nonsense phrase ETAOIN SHRDLU represents the 12 most frequent letters in typical English language text.

In some ciphers, such properties of the natural language plaintext are preserved in the ciphertext, and these patterns have the potential to be exploited in a ciphertext-only attack.

xcrgneipcpanhxhugtfjtcrnpcpanhxhxhiwthijsnduiwtugtfjtcrnduatiitghdgvgdjehduatiitghxcprxewtgitmiiwtbtiwdsxhjhtsphpcpxsidqgtpzxcvraphhxrparxewtghugtfjtcrnpcpanhxhxhqphtsdciwtupriiwpixcpcnvxktchigtirwdulgxiitcapcvjpvtrtgipxcatiitghpcsrdbqxcpixdchduatiitghdrrjglxiwkpgnxcvugtfjtcrxthbdgtdktgiwtgtxhprwpgpritgxhixrsxhigxqjixdcduatiitghiwpixhgdjvwaniwthpbtudgpabdhipaahpbeathduiwpiapcvjpvtudgxchipcrtvxktcphtrixdcdutcvaxhwapcvjpvttippcsdpgtiwtbdhirdbbdclwxatofmpcsypgtgpgtaxztlxhtiwtgdcpcspcpgtiwtbdhirdbbdcepxghduatiitghitgbtsqxvgpbhdgsxvgpewhpcshhttiipcsuupgtiwtbdhirdbbdcgtetpihiwtcdchtchtewgphttipdxchwgsajgtegthtcihiwtbdhiugtfjtciatiitghxcinexrpatcvaxhwapcvjpvtitmixchdbtrxewtghhjrwegdetgixthduiwtcpijgpaapcvjpvteapxcitmipgtegthtgktsxciwtrxewtgitmipcsiwthtepiitgchwpktiwteditcixpaidqttmeadxitsxcprxewtgitmidcanpiiprz

Task 2.1 - Craftin’ a Frequency Table

In a python file, create a frequency table o’ the letters in the English tongue. Ye can try and find this yerself, but if ye be not inclined to do so, we understand that, aye!

If ye truly wish to find it yerself, ye can do as in Task 2.2, but on a right large text.

english_letter_frequency = {
    'E': 12.70, 
    'T': 9.06, 
    'A': 8.17, 
    'O': 7.51, 
    'I': 6.97, 
    'N': 6.75, 
    'S': 6.33, 
    'H': 6.09, 
    'R': 5.99, 
    'D': 4.25, 
    'L': 4.03, 
    'C': 2.78, 
    'U': 2.76, 
    'M': 2.41, 
    'W': 2.36, 
    'F': 2.23, 
    'G': 2.02, 
    'Y': 1.97, 
    'P': 1.93, 
    'B': 1.29, 
    'V': 0.98, 
    'K': 0.77, 
    'J': 0.15, 
    'X': 0.15, 
    'Q': 0.10, 
    'Z': 0.07
}

Task 2.2 - Countin’ the Frequency o’ Letters in a Text

Now, we be makin’ an algorithm t’ find the frequency o’ letters in a given text.

Task 2.3 - Compare the frequency o’ a text with the true frequency

Once ye’ve found the frequency o’ all the letters in the text, ye can craft a function that finds the “distance”. Arrr? What be meant by that?!

Ye can picture the frequency o’ somethin’ like E in the text bein’ a number. Ye can find the “distance” this has with the actual frequency, which be 12.70. Example: The frequency be 9.63, what be the distance? The distance be the absolute value (negative numbers become positive) between these two values: \(12.70 - 9.63 = 3.07\).

Craft a function that goes through each o’ the letters and finds the distance. Then, add all the distances together to a “total” distance.

Task 2.4 - “Crack” the Caesar Cipher

Now we shall finally put together all we have done so far! Now we shall “crack” a Caesar cipher.

Create a program that “cracks” a Caesar cipher! Without user input, ye be able to toss in an encrypted text and retrieve the decrypted text without needin’ a key.