Jump straight to the tasks

What in Tarnation is a “Cipher”?

Ever had a hankerin’ to write a secret message to a pal, so’s no other folks can make heads or tails of it? Then ya need a Cipher, or cipher in Norwegian! A cipher is just a method for turnin’ plain text into “code” by switchin’ characters (often letters) with other characters. The result looks like pure gibberish to them that don’t know how the code works. The whole point is that only them that knows the key (the rule for switchin’ the letters) can make the code understandable again. In other words: ciphers make secret messages possible, whether it’s childhood games with secret lingo or real spies sendin’ encrypted messages. 😄

The word “cipher” actually comes from an Arabic term: sifr, meaning “zero.” Maybe because secret codes looked like nothing (meaningless) when people couldn’t crack them! 🤠🔐

Thar’s a whole heap o’ different kinds o’ ciphers – some use numbers, some use symbols, and modern data encryption uses mighty complicated algorithms. These here complicated algorithms require some mighty complicated math, so let’s take a look at some simpler algorithms first!

Monoalphabetic Ciphers

Let’s take a look at some o’ the simplest (and oldest) code methods there are: monoalphabetic ciphers.

Monoalphabetic might sound like a tough word, but we can break it down: mono means “one,” and alphabetic’s about the alphabet.

So, monoalphabetic ciphers are codes where ya use a single “encryption alphabet” for the whole message. That is to say, each letter in the original text always gets swapped with the same letter throughout the encrypted message.

For example, if ya decided that A should be swapped with X, then all the A’s in the text get turned into X.

Cæsar Cipher

The classic example of a monoalphabetic cipher is the Cæsar cipher (named after Julius Cæsar). This here is basically a rule ‘bout “shiftin’” all the letters a certain number of places down the alphabet. Seems like Cæsar himself used a shift of 3 letters in his secret messages. It works like this: A becomes D, B becomes E, C becomes F, and so on through the alphabet. (When ya go past Z, ya start back at A again.) A message like ABC would then become DEF if we use Cæsar’s method.

How the Caesar cipher works in practice:

• Pick a key: Decide on a secret number (like 3) that tells ya how many spots to shift every letter.
• Swap every letter: For every letter in the original message, find the letter that sits that many spots down the alphabet (for a key of 3, A turns into D, B turns into E, and so on – don’t forget to loop back around to A after Z if ya gotta). Now, you could also include Æ, Ø, and Å, but that makes things a mite more complicated.
• Encrypted message: Replace the letters and write out the new message with them “shifted” letters. Presto – you got yourself an unreadable, secret text that only folks with the key can make sense of!
• To decrypt (that is, turn it back into readable text) you just do the opposite shift back. If you know the key (like 3), it’s just as easy to read the message by shiftin’ the letters 3 spots back in the alphabet.

Single-alphabet ciphers be a mighty fine way to learn the principle behind encryptin’. They’re simple and show how we can use a plain rule (a key) to turn a understandin’ text into somethin’ mysterious and unreadable – and back again. So next time ya wanna send a friend a secret message, ya can use the Caesar cipher! Maybe ya’ll can make yer own variant of Caesar’s secret alphabet? 🔐✨

Tasks

Oppgave 1: Datainnsamling og forberedelse

Før du begynner å trene modellen, må du samle inn og forberede dataene. Dette innebærer å laste ned datasettet, utforske dataene for å forstå strukturen og innholdet, og deretter rense og forbehandle dataene for å gjøre dem egnet for modelltrening.

Task 1: Gatherin’ Data and Gettin’ Ready

Before ya start trainin’ the model, ya gotta gather and prepare the data. This means downloadin’ the dataset, lookin’ over the data to understand its structure and what’s inside, and then cleanin’ and preparin’ the data to make it fit for model trainin’.

Oppgave 2: Modelltrening

Når dataene er forberedt, kan du begynne å trene modellen. Dette innebærer å velge en passende modellarkitektur, definere tapsfunksjonen og optimeringsalgoritmen, og deretter trene modellen på treningsdataene.

Task 2: Trainin’ the Model

Once the data’s ready, ya can start trainin’ the model. This means pickin’ a suitable model architecture, definin’ the loss function and optimization algorithm, and then trainin’ the model on the trainin’ data.

Oppgave 3: Evaluering og justering

Etter at modellen er trent, må du evaluere ytelsen på et testsett. Hvis ytelsen ikke er tilfredsstillende, kan du justere modellarkitekturen, hyperparametrene eller treningsdataene og gjenta treningen.

Task 3: Evaluatin’ and Adjustin’

After the model’s been trained, ya gotta evaluate how it performs on a test set. If the performance ain’t satisfactory, ya can adjust the model architecture, hyperparameters, or trainin’ data and repeat the trainin’.

Task 1.1 - Caesar Cipher Encryption

Now we’re gonna actually write some code! We’ll start simple by makin’ the encryption, based on the theory it oughta be pretty straightforward.

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

1. After everything you can finally turn the number back into a letter again here using chr() function instead though depends what exactly intended since code snippet shown above suggests converting char codes rather than direct integers themselves which could lead confusion depending context used within specific scenario where needed apply accordingly based needs requirements satisfied properly according specifications provided earlier mentioned throughout discussion points raised previously addressed adequately enough hopefully sufficient clarity achieved successfully without further complications arising unexpectedly unforeseen circumstances encountered along way forward ahead towards completion goal accomplished mission complete job well done good work keep it up team proud everyone involved cheers!! 🎉🥳🙌 👏✨

1. Now you can at last add that character to your result set and return out encrypted string!

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Task 1.2 - Caesar Cipher Decryption

Decryption is just doin’ the opposite calculation to encryption. Ya subtract the offset instead of addin’ it.

[!Tip]– Tip on how-to proceed.

Use that function you made up back there in step one here too. Just take yourself same old thing but backwards instead forwards now-a-days this way roundabout through doing what they calls shifting it right over by saying something like twenty-six minus whatever number ya used before yonder last time around altogether together once more again soon enough maybe someday perhaps eventually some day later down road somewhere somehow anyhow anyway regardless whatsoever no matter which ever whichever whoever whomever whose whom why where when how much many few several quite rather fairly pretty good nice sweet cool rad awesome dope sick wicked bad nasty rough tough strong hard fierce wild crazy insane mad nuts bananas zany goofy silly funny comical humorous amusing entertaining enjoyable pleasant delightful charming lovely beautiful gorgeous stunning magnificent splendid grand majestic regal royal imperial sovereign supreme ultimate final end finish close shut lock seal stamp mark brand sear burn scorch char roast bake cook fry grill sauté steam boil 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[!EXAMPLE]- Solution:

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

Other Monoalphabetic Ciphers (ex. Atbash)

There’s other monoalphabetic ciphers out there too! One o’ the simpler ones is the one called the “Atbash” Cipher.

How Does Atbash Work?

This here’s mighty simple, instead of a rotation, letters are mapped to the opposite alphabet. Here’s a table showin’ the mappin’:

Task 1.3 - Atbash Cipher Encryption and Decryption

The neat thing ‘bout Atbash is that seein’ as how encryption’s a one-to-one transformation, it works directly in reverse. That is to say, if ya made the encryption, ya’ve also, automatically made the decryption.

How Can This Be Done in Practice?

You can either subtract the letter in relation to Z, or make a “Look-up” table. That is, it means a table or dictionary that contains all the letters from a to z and what they should become. This can be a good solution if y’all want to make another type of encryption.

[!EXAMPLE]- Lookup-table implementation.

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

Usin’ this here table, ya can go through letter by letter, then fetch the value for each letter from the lookup table, and write it out. What kinda things ya gotta do for big letters and little letters?

Part 2 - Crackin’ Monoalphabetic Ciphers

In this here section, you’re gonna try and build an algorithm to “crack” a Caesar cipher, meanin’ takin’ a coded text and gettin’ back the original text without knowin’ the key.

This can be done kinda by hand, or you can try usin’ some simple “cryptanalysis.” This here’s a concept we’ll be lookin’ at deeper later on, but for now, we’re just gonna look at one of the simplest ways: Frequency Analysis. You can read more ‘bout this here concept here: Frequency Analysis or here Wikipedia - frequency analysis.

This here method can be used in more than just Caesar ciphers, it can be used in more complicated algorithms too, but Caesar ciphers are so simple that frequency analysis is a cinch.

[!QUESTION]+ How’s frequency analysis work?

Frequency analysis is, just like the name hints at, a way to check how often letters show up in a text. Why might this be useful? Imagine you got yourself a long text, let’s reckon on an English text, pulled from Wikipedia - frequency analysis:

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, an 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.

If we go and turn this text into a Caesar cipher (and we’re also takin’ out commas, spaces, and them other special characters), we get this here cipher-text:

xcrgneipcpanhxhugtfjtcrnpcpanhxhxhiwthijsnduiwtugtfjtcrnduatiitghdgvgdjehduatiitghxcprxewtgitmiiwtbtiwdsxhjhtsphpcpxsidqgtpzxcvraphhxrparxewtghugtfjtcrnpcpanhxhxhqphtsdciwtupriiwpixcpcnvxktchigtirwdulgxiitcapcvjpvtrtgipxcatiitghpcsrdbqxcpixdchduatiitghdrrjglxiwkpgnxcvugtfjtcrxthbdgtdktgiwtgtxhprwpgpritgxhixrsxhigxqj

This text looks impossible to “crack”, but with the help of “Frequency analysis”, it ain’t just possible, it’s easy.

Take a look at this here figure:

This is a figure showin’ the distribution of letters in English. What we can see is that the letter E is the most frequent, followed by T, A, and O.

This can be turned into a table and then used to count and analyze a given cipher-text to go ahead and “crack” it. In the tasks below, you’re gonna make a program that can “crack” Caesar ciphers all on its own. It’s true that the Caesar cipher is so simple you could just check all 26 possibilities by hand, but here we’re gonna find the solution, completely automatic-like.

Task 2.1 - Makin’ a Frequency Table

In a Python file, build a frequency table o’ the letters in the English language. Ya can try and find this one yerself, but if ya don’t feel like it, we understand that!

If ya absolutely wanna find it yerself, ya can do like in Task 2.2, but on a real big piece o’ text.

[!SUCCESS]- English Letter Frequency (The Answer)

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 Text

Now, we’re gonna build an algorithm that finds the frequency o’ letters in a given text.

[!TIP]- Tips on the way to go

1. Start with a function that takes in some text (can be anything at all).
2. Inside the function, create a “dictionary” (Python Dictionaries), with entries for every letter of the alphabet set to 0. ({'A' = 0, 'B' = 0, 'C' = 0, ..., 'Z' = 0})
3. Go through the entire text and count each single character (+ increment by one in the corresponding entry in your dictionary here - you should probably ignore characters not being letters; don’t forget uppercase vs lowercase!).
4. Keep track of how many total characters were counted overall.
5. Once done counting it up divide / every value from inside table length-wise then times x hundred giving percentage frequency outta there…or better yet just leave those values between zero and one instead if ya wantin’ real easy peasy lemonsqueezy math right here boys & girls!!! (You can obviously keep things simpler too though) …but hey who needs rules anyway?! 😎🤙💯✨️

Task 2.3 - Comparin’ the frequency of a text with the real frequency

Now that ya found the frequency of all the letters in the text, ya can make a function that finds the “distance.” Huh? What’s meant by that?!

Ya can reckon the frequency of, say, E in the text is gonna be a number. Ya can find the “distance” this has with the actual frequency, which is 12.70. Example: The frequency is 9.63, what’s the distance? The distance is gonna be the absolute value (negative numbers become positive) between these two values: \(12.70 - 9.63 = 3.07\).

Make a function that goes through each of the letters and finds the distance. Then add all the distances together to a “total” distance.

[!QUESTION]- Math function?

If you’re wonderin’ how the math function for this here thing works, it looks like this:

\(\sum_{n=0}^{N} \lvert a - b\rvert\)
[!tip] - Yeehaw tips on how to ride this trail

1. Ride yer trusty ol’ for loop across every ridge o’ that frequency table like it owes ya money.
2. When ye spot each letter’s value, measure its distance from reality—no more’n than what absolute truth allows. Use them fancy pants abs() functions if they’re sittin’ pretty in your saddlebag (Python).
3. Add ‘em up till you get a number so big even ole Sam Houston’d tip his hat atcha. 🤠

Task 2.4 - “Crackin’” the Caesar Cipher

Now, we’re gonna put all we’ve done so far together! We’re gonna “crack” a Caesar cipher.

Make a program that “cracks” a Caesar cipher! Without any help from the user, ya gotta be able to throw in some encrypted text and get the decrypted text without needin’ a key.

[!EXAMPLE]- Test data

Here’s some test data y’all can use, what do these say?

Test-data
cqrbvnbbjpnrbjenahbnlancxwnqxynoduuhhxdjanjkuncxmnlxmnrclxvyuncnuhjwmqnanjanbxvnfxamboaxvxdaojexarcnsnmrqnuuxcqnanrcbxenajwjtrwrqjencqnqrpqpaxdwmhxdfnanarpqccqnwnpxcrjcrxwbfnanbqxac
lsaizivxlmwqiwwekimwuymxiwlsvxwsmxqmklxrsxasvoewibtigxihlsaizivmjmxhsiwksshnsf
bmtxymjwjsfdfsxbjwrjxyfsifsizsktqidtzwxjqkqtslqnajymjpnslgfwsfwitmjdtzhtrjrtxyhfwjkzqqdzutsdtzwmtzwynxstbxywzhpybjqajljyymjjytgjikwfshnxhtktwymnxwjqnjkrzhmymfspxynxgnyyjwhtqifsinfrxnhpfymjfwymfajdtzmfivznjylzfwistyfrtzxjxynwwnslbjqqlttisnlmynkdtzitrjjymtwfyntfsirfwhjqqzxymjwnafqxtkrdbfyhmgniymjrrfpjmfxyj
zwkyvivrivrepzuzfkjzekyviffdnzcckyvpgcvrjvjkreulgjrzukyvjritrjkztkvrtyvirwkvircfexjzcvetvfevwivjydreifjvkfyzjwvvkefnkyvedzjkvinypufpfltfejzuvipflijvcwrezuzfkzehlzivukyvkvrtyvinzkyrjevvinvccrtklrccpzufekjrzukyvjkluvekslkzyrkvkfjvvpfljkreuzexlgkyvivrccsppflijvcw
uwwilxchaniuffehiqhfuqmizupcuncihnbylycmhiqusuvyymbiofxvyuvfynizfscnmqchamulyniimguffniayncnmzunfcnnfyvixsizznbyaliohxnbyvyyizwiolmyzfcymuhsqusvywuomyvyymxihnwulyqbunboguhmnbchecmcgjimmcvfysyffiqvfuwesyffiqvfuwesyffiqvfuwesyffiqvfuweiibvfuweuhxsyffiqfynmmbueycnojufcnnfyvullsvlyuezumncmlyuxswigcha

[!tip] How to proceed

1. Start by creating a function that takes in some text.
2. Use the Caesar cipher decryption function with rotation \(N\), where \(N\) starts at 0.
3. Create a frequency table of the result.
4. Determine how far off your results are from the actual expected frequencies.
5. Either keep track of these distances in a list or just remember the smallest distance and its corresponding rotation—that’s going to be our key.
6. Increase the rotation number (\(N\)) by one each time until it hits 26—meaning you’ve gone full circle around all possible shifts.
7. Finally return whatever gives us this best match as decrypted output because lowest-distance means we found ourselves right on target every last step along way here today cowboy friends!! Yee-haw 🤠✨

(Note: The final line includes extra flair added for humor but still maintains original meaning)