We’re fascinated by secrets. From the whispered password that opens a hidden door to the complex algorithms that protect our digital lives, the art of concealing information—cryptography—has always held a certain mystique. But what if a secret code wasn’t hidden in a jumble of random letters or numbers, but in the very rhythm and sound of language itself? What if the key to a cipher was a poem, and the lock was an understanding of phonetics?

This isn’t about the Enigma machine or blockchain technology. Instead, we’re diving into a thought experiment at the intersection of linguistics and espionage: using poetic devices like alliteration and assonance as a simple, elegant form of steganography.

A Quick Refresher: The Music of Language

Before we build our cipher, let’s tune our ears to the building blocks we’ll be using. Most of us learned about alliteration and assonance in English class, but let’s revisit them from a linguistic perspective.

• Alliteration is the repetition of the same consonant sound at the beginning of words in a phrase or sentence. The key here is the sound, not the letter. For example, “cool kids” is alliterative because both words start with the /k/ sound, even though the letters are different.
• Assonance is the repetition of the same vowel sound within words, regardless of the surrounding consonants. It’s what makes the line “The rain in Spain stays mainly on the plain” so memorable. All those words share the same /eɪ/ vowel sound. Again, it’s about the sound, not the spelling. “Try to light the fire” demonstrates assonance with the /aɪ/ sound.

These devices are the heart of poetry and prose, creating rhythm and musicality. But for our purposes, they are also the secret signs that point to a hidden message.

The Bard’s Cipher: How It Works

Let’s propose a hypothetical system: the Bard’s Cipher. Unlike traditional ciphers where a key might be a word (like “LEMON”) or a number, the key in the Bard’s Cipher is a set of rules based on phonetic patterns.

The sender and receiver must agree on this key beforehand. It could be something as simple or as complex as they like. For our example, let’s establish the following two-part key:

The Key:

1. If a line of text contains alliteration, the secret letter is the first letter of the third word in that alliterative cluster.
2. If a line of text contains assonance with the long “A” sound /eɪ/ (as in “say”, “main”, “great”), the secret letter is the first letter of the second word in that assonant cluster.

Any line that doesn’t meet these specific criteria is simply filler, designed to make the text look natural and conceal the lines that do contain information. The magic of this system is that the resulting message doesn’t look like code at all. It just looks like a paragraph of (perhaps slightly over-written) text. This is a form of steganography—the practice of hiding a message within another, seemingly innocuous message.

Crafting a Message: A Step-by-Step Example

Now, let’s put the Bard’s Cipher into action. Imagine we need to send the secret message “SEND HELP” to our fellow agent, who knows our two-part key. We need to craft a short piece of text where specific lines will yield these letters when decoded.

Here’s a message we could write:

It was a strange morning at the docks. Silent snakes slithered slowly; I saw one by the crates. Big boats bobbed endlessly on the water, their horns groaning a low note. An announcement was made, saying they made a name for themselves by being punctual. Dreadful dragons did damage to the pier last year, according to local legend. A great day had finally come for repairs. Fierce fish fought eagerly against the lines of the fishermen. They claimed the main game lingered for hours. Pretty parrots prattled perpetually from the rooftops of the warehouses, adding to the general noise. It was all too much.

To an outsider, this is just a descriptive, if slightly purple, paragraph. But to our recipient, it’s a treasure map. Let’s decode it using our key:

• S: “Silent snakes slithered…” This is alliteration. Rule 1 applies. The third word is “slithered.” The first letter is S.
• E: “Big boats bobbed…” This is alliteration. Rule 1 applies. The third word is “bobbed.” But wait, that gives us ‘B’. This highlights a key challenge: the writer must be precise! Let’s revise the source text. A better sentence would be: “Big boats brought everyone to shore.” The third word is “everyone.” The first letter is E. Let’s use this revised version for our decoding.
• N: “they made a name…” This is assonance with the /eɪ/ sound. Rule 2 applies. The second word in the cluster is “name.” The first letter is N.
• D: “Dreadful dragons did…” Alliteration. Rule 1 applies. The third word is “did.” The first letter is D.
• H: “a great day had…” Assonance with the /eɪ/ sound. Rule 2 applies. The second word in the cluster is “had.” The first letter is H.
• E: “Fierce fish fought…” Alliteration. Rule 1 applies. The third word is “fought.” Another mistake! We need ‘E’. Let’s revise again: “Fierce fish found everything they wanted.” The third word is “everything.” The first letter is E.
• L: “the main game lingered…” Assonance with /eɪ/. Rule 2 applies. The second word is “lingered.” The first letter is L.
• P: “Pretty parrots prattled…” Alliteration. Rule 1. The third word is “prattled.” The first letter is P.

As you can see, even a simple message requires careful, deliberate construction. Our decoded message, after some on-the-fly author corrections, is: S-E-N-D H-E-L-P.

Strengths and (Many) Weaknesses

While you probably shouldn’t use the Bard’s Cipher to protect your bank account details, it’s a fascinating concept with a unique set of pros and cons.

Strengths:

• Inconspicuous: Its greatest strength is that it doesn’t look like a code. It can pass through casual inspection without raising any flags, a huge advantage in steganography.
• Abstract Key: The key is a concept, not a string of text. It can be memorized and shared verbally, leaving no physical or digital trace.
• Resistant to Standard Computation: A computer program looking for letter frequency (like in a substitution cipher) would find nothing unusual. Cracking it would require sophisticated natural language processing capable of identifying phonetic patterns accurately.

Weaknesses:

• Highly Inefficient: As our example showed, it takes a lot of words to encode a very short message. This is known as low data density.
• Difficult to Author: Writing prose that sounds natural while embedding a specific, structured message is incredibly difficult and time-consuming. It often ends up sounding forced and unnatural, which could itself be a giveaway.
• Prone to Ambiguity: This is the fatal flaw. What one person considers strong assonance, another might not notice. Accents and dialects are a huge problem; the “cot-caught merger” in American English means some speakers pronounce two different vowels identically. If the sender and receiver have different accents, the message could be completely garbled.

More Than Just a Code

The Bard’s Cipher is, ultimately, a playful thought experiment. It reminds us that structure and information can be hidden in the most unexpected places. It pushes us to see language not just as a tool for communication, but as a layered system of sounds, rhythms, and patterns.

So the next time you read a poem or listen to a well-crafted speech, pay attention to the music of the words. Listen for the subtle chains of alliteration and the echoes of assonance. There might not be a secret message hidden within, but you’ll be appreciating the deep, intricate, and beautiful code that is human language.