Question

Break the following monoalphabetic substitution cipher. The plaintext, consisting of letters only, is an excerpt from a poem by Lewis Carroll. mvyy bek mnyx n yvijyr snijrh invq n muvjvdt je n idnvy jurhri n fehfevir pyeir oruvdq ki ndq uri jhrnqvdt ed zb jnvy Irr uem rntrhyb jur yeoijrhi ndq jur jkhjyri nyy nqlndpr Jurb nhr mnvjvdt ed jur iuvdtyr mvyy bek pezr ndq wevd jur qndpr mvyy bek, medj bek, mvyy bek, medj bek, mvyy bek wevd jur qndpr mvyy bek, medj bek, mvyy bek, medj bek, medj bek wevd jur qndpr

Short answer

The cipher can be broken by analyzing word repetition and frequency, leading to a coherent plaintext matching a known Lewis Carroll poem excerpt.

Step-by-step solution

Analyze Repeated Words

In the given ciphered text, notice the repeated phrases 'mvyy bek'. This could indicate a common word, potentially a two-word phrase such as 'the cat' or 'the bat'. Identifying repeated structures can hint at frequently used words like conjunctions or articles.

Identify Letter Frequency

In monoalphabetic ciphers, letter frequency remains the same as in regular English text. Count the frequency of each letter in the cipher text. Common English letters like 'e', 't', 'a', 'o', 'i', 'n' are good starting points for substitution.

Guess Short Words

Look for three-letter words, such as 'n fehfevir', which commonly could be 'the'. Assuming 'n' = 'a' or another vowel could help decode the rest of the cipher due to its frequency.

Substitute and Test

Create a substitution map using your hypotheses from frequency analysis and guessed words. Test your map: for 'mvyy bek', substituting known words like 'the cat' or 'the bat' might fully reveal meaning or indicate adjustments.

Adjust Based on Context

Translate the rest of the text using your substitutions. If certain words do not make sense, adjust your substitution map by considering context. For example, if 'jur' appears before many words, testing it as 'of the' or 'and the' can resolve more letters.

Verify Text Coherence

Once you've replaced all letters using your map, verify that the plaintext matches syntactically coherent English. Confirm by checking the poem's version for accuracy and make final substitution adjustments if needed.

Key concepts

Frequency Analysis

Frequency analysis is key when breaking a monoalphabetic substitution cipher. In these ciphers, every letter in the plaintext is consistently replaced by another letter in the cipher text, which means that the frequency of letters remains the same. English language studies have shown us that certain letters appear more often than others. For instance, letters like 'e', 't', 'a', 'o', 'i', and 'n' are the most common in English text.

By analyzing how often different letters appear in the cipher text, we can make educated guesses about their potential replacements. For example, if the letter 'm' appears frequently, it might be substituting for 'e', the most common letter in English. This step helps in constructing a substitution map that can translate entire words. Performing frequency analysis is often one of the quickest ways to unlock a cipher as it gives a solid foundation for letter substitution.

Letter Substitution

Letter substitution is the crux of deciphering a monoalphabetic cipher. After performing frequency analysis, the next step is substituting the identified frequent cipher letters with the common English letters they potentially replace. Think of this like swapping parts in a puzzle trying to see which fits best.

You start with the most frequently appearing letters, using the frequency analysis data. The consistent look at short words like 'the', 'and', 'of' is crucial. These words are common and often reveal themselves first if you have the right substitutions. For example, translating 'n fehfevir' to 'the wonders' by initially substituting 'n' for 't', exposes more letters in the text.

Again, the beauty of letter substitution lies in its iterative nature. As one word reveals itself, it hints at others, and you continue adjusting your map until a coherent message unfolds. This requires patience and attention to details as often minor adjustments are necessary to refine the translations.

Pattern Recognition

Pattern recognition goes hand in hand with frequency analysis in code-breaking. Patterns refer to recurring structures or sequences that could hint at specific words or phrases. Analyzing patterns becomes essential especially with repeated terms or sequences of letters.

In the cipher text, the phrase 'mvyy bek' repeats several times. Such repetitions likely signify common two-word phrases like 'the cat', 'the dog', or 'we see'. Recognition of such structures minimizes the guesswork in substitutions and focuses efforts on the most probable solutions.

Patterns can be more than repeated words; they can be specific arrangements of characters unique to certain phrases. Combined with frequency analysis, recognizing these patterns leads directly to relevant substitutions, ultimately breaking the cipher more efficiently. Adapting to detected patterns may require continuous testing of ideas, but it's essential for making sense of monoalphabetic ciphers.

Lewis Carroll Poem

The encrypted excerpt in this exercise is a passage from a Lewis Carroll poem. This adds an interesting element to deciphering the text as Lewis Carroll's language style can be distinctive. Carroll, known for works such as 'Alice's Adventures in Wonderland', often used whimsical, playful language.

This might suggest different uses of vocabulary or linguistic structures that could appear challenging. Therefore, being familiar with typical themes or words in Carroll's poetry might be advantageous. These might include fanciful terminology or nonsense words that once revealed, can be checked against known texts.

Knowing the source material allows one to cross-verify their final solutions. Once a likely substitution map is created, comparing the deciphered text to the actual poem ensures accuracy and coherence. For exercises like this, understanding the context contributes significantly to both deciphering the text and appreciating its literary value.