Hi,

Is there anyone here who is good at ciphers who would be willing to help me create a cipher to encrypt/encode a letter to my character from her childhood friend and former lover, now turned enemy?

I am going to have the letter commissioned on an actual scroll but I wanted the scroll to be unreadable by anyone who didn't know the cipher.

But I don't even know how to go about creating one, let alone using it for an entire letter.

Cherrs

You tried Google? Here are some simple ciphers from Wikipedia. https://en.m.wikipedia.org/wiki/Classical_cipher

I did, yes and I thought about using them but if I could write a letter using those ciphers, others who are more familiar with ciphers and codes, would be able to break the cipher and read the letter.

The letter is supposed to hide an extremely important plot point regarding the characters story.

So it seems like nothing more than a letter of regret, written from a former lover but deciphering the letter would reveal the truth.

The enciphered letter, would then be hidden behind a very basic code, to make it unreadable to most people.

Rogues and such, could break this code though - but then all they would find is a letter of regret from a former lover.  They shouldn't be able to decipher the letter and ascertain it's true meaning.

I had thought about making the letter magical.  So literally its true meaning was hidden by magic.

The NPC who wrote the letter though is entirely none magical and possesses no magical ability at all.  Add to that, using magic on something as simple as a letter would be a dead give away that, that letter was more than it seemed.

Thus, I was wanting something that would present an actual puzzle to anyone who might steal the letter or try to read it.

Quote from Stormknight >>

This website allows you to encrypt and decrypt passages of text, using various ciphers:

https://cryptii.com/

The various "substitution ciphers" are probably the ones you want to use.

Oh thanks XD

A simple Caesar cipher probably will be cracked, but a Vigenère square cipher is almost impossible to crack without the keyword (a computer could crack the keyword given time).

https://www.youtube.com/results?search_query=encryption computerphile

The above link is all the resources you would need for a rundown on ciphering.

Below is some thematic element you can use to interact with your party, for instance maybe they know the "ally" and can get his key, but they can't decrypt the message just yet because of the following principle illustrated in the below thought problem.

Question: How do you send a message to your ally in a locked box without sharing the key so that the enemy cannot intercept the key and the box and get the message?

*Pauses to let you think about that for a while*

Answer: Person A puts lock A on the box, sends his ally the box. Ally puts lock B on the box sends the box back with both Locks A and B. Person A removes lock A, sends back the box. His ally removes his own lock B.

This in principle is the modern concept of all encryption. Keys are not shared, and keys are agreed upon by complex mathematical formulas without either party ever knowing what those keys actually are. How complex? Here's the most "entry level" example I can think of.

C = M^e(Mod(p-1)(q-1))

M=C^d(Mod(p-1)(q-1))

Where  (e)(d)= 1(p-1)(q-1)

M= message, converted to number (such as bits)

C= Cipher

p and q are relatively simplistic but explaining them is hard for me right now.

In the game, your key could be as simple as the "locked box" analogy where the box cannot be destroyed or the message is also destroyed.

https://en.wikipedia.org/wiki/RSA_(cryptosystem)

The above formula basically describes RSA encryption.

Which addresses the "how to lock a box and send it without sending the key" problem.

Back to the story, I think the Vigenère cipher works, and maybe the lover has the other key and it's lost now so you aren't able to decipher the "CIPHERTEXT" and instead have to try and crack it?

You sent her a love letter, she sent it back having altered the letter, indicating that every 4th letter was now a code but she shifted the PLAINTEXT using her Vigenère KEY (but you don't know what her KEY was). So you encrypted this CIPHERTEXT hidden in the letter with your own KEY and sent it back so that she could remove her encryption and return it to you so when you removed yours you would know the secret message. When the letter never returned you later recovered it, and found that your KEY would not decipher the CIPHERTEXT, meaning she did not Remove the encryption she added using her KEY.

You do not know if she never touched the CIPHERTEXT, or if she, for some reason unknown to you, added another round of encryption to it.

After a while failing to decrypt it by brute force, you encrypted the whole letter in a magical Vigenère cipher that players can attempt to decrypt themselves, to reveal just a Love Letter. It's up to them to discover that there's a message within the message, further encrypted.

To summarize the story point.

1. Write a love letter
2. Write the lover's secret message
3. Hide the lover's secret message in the love letter with the trick of "first letter of every word is the secret message".
4. Encrypt the secret message using a cipher like Vigenère with a certain key
   1. That key is not known to the character
5. Character runs his own Vigenère with a certain key over that encrypted secret message.
6. Decide if you want to add another layer of encryption to the secret message (with another key) by the lover.
7. Lastly, come up with a simple substitution that masks the encrypted message (now multiple encryptions with multiple keys) back to the letters they are supposed to be.
   1. In practice, let's say every first letter of each sentence is the Secret Message. Next to each first letter is a number (positive or negative) and the number represents how far you shift the letter to the left or right to come to the last layer of encryption.
   2. This is such a simple substitution but it allows the letter to read without typos.
8. Encrypt the whole message with a Vigenère cipher (including the encrypted message.)

Quote from IDNeon357 >>

To summarize the story point.

1. Write a love letter
2. Write the lover's secret message
3. Hide the lover's secret message in the love letter with the trick of "first letter of every word is the secret message".
4. Encrypt the secret message using a cipher like Vigenère with a certain key
   1. That key is not known to the character
5. Character runs his own Vigenère with a certain key over that encrypted secret message.
6. Decide if you want to add another layer of encryption to the secret message (with another key) by the lover.
7. Lastly, come up with a simple substitution that masks the encrypted message (now multiple encryptions with multiple keys) back to the letters they are supposed to be.
   1. In practice, let's say every first letter of each sentence is the Secret Message. Next to each first letter is a number (positive or negative) and the number represents how far you shift the letter to the left or right to come to the last layer of encryption.
   2. This is such a simple substitution but it allows the letter to read without typos.
8. Encrypt the whole message with a Vigenère cipher (including the encrypted message.)

Oh I think I might have made a mistake with this.  Both the NPC and my character are only teens.

I am not sure a teen would know how to do all of this really.

Quote from SocialFoxes >>

Quote from IDNeon357 >>

To summarize the story point.

1. Write a love letter
2. Write the lover's secret message
3. Hide the lover's secret message in the love letter with the trick of "first letter of every word is the secret message".
4. Encrypt the secret message using a cipher like Vigenère with a certain key
   1. That key is not known to the character
5. Character runs his own Vigenère with a certain key over that encrypted secret message.
6. Decide if you want to add another layer of encryption to the secret message (with another key) by the lover.
7. Lastly, come up with a simple substitution that masks the encrypted message (now multiple encryptions with multiple keys) back to the letters they are supposed to be.
   1. In practice, let's say every first letter of each sentence is the Secret Message. Next to each first letter is a number (positive or negative) and the number represents how far you shift the letter to the left or right to come to the last layer of encryption.
   2. This is such a simple substitution but it allows the letter to read without typos.
8. Encrypt the whole message with a Vigenère cipher (including the encrypted message.)

 

Oh I think I might have made a mistake with this.  Both the NPC and my character are only teens.

I am not sure a teen would know how to do all of this really.

If you want it to be in character, the simple substitution (Caesar cipher) would make sense, the layers of encryption would make total sense because it would be like a little game they would have done. So that is not too complex.

Remove the idea of the magical encryption at the end, unless it occurs later and the character has more knowledge?

Quote from SocialFoxes >>

Oh I think I might have made a mistake with this.  Both the NPC and my character are only teens.

I am not sure a teen would know how to do all of this really.

 A simple substitution cipher that is a little more secure than a shifted cipher is is the mixed alphabet cipher. It can use a key word or phrase that only uses each letter once and the remaining letters in order after that. For example:

ABCDEFGHI JKLMNOPQRSTUVWXYZ

PRI VATEBCDFGHJKLMNOQSUWXYZ

Another classic is get a strip of paper that is only one letter high, can be as long as you like. Now wrap it around something, a pencil (short message), broom handle (longgggggg message lol) something that both parties would have. Starting at the beginning of the paper strip write your message down the length of what you have wrapped the paper around, when you get to the bottom of the pole, you can either continue at the bottom working your way up or start again at the top working down.

Once the strip of paper has been unwrapped, it will just show a string of letters in no particular order, this can be solved in two ways 
1. having the same size pole to wrap the paper around
2. knowing the spacing so they can just read say every 3rd letter to spell out the message.

This is a very basic cyphering system which is made difficult by its simplicity, here is a link for you that might explain it better lol

https://en.wikipedia.org/wiki/Scytale