ciphers.caesar_cipher

Attributes

choice

Functions

brute_force(→ dict[int, str])

brute_force

decrypt(→ str)

decrypt

encrypt(→ str)

encrypt

Module Contents

ciphers.caesar_cipher.brute_force(input_string: str, alphabet: str | None = None) → dict[int, str]

brute_force

Returns all the possible combinations of keys and the decoded strings in the form of a dictionary

Parameters:

  • input_string: the cipher-text that needs to be used during brute-force

Optional: * alphabet: (None): the alphabet used to decode the cipher, if not

specified, the standard english alphabet with upper and lowercase letters is used

More about brute force

Brute force is when a person intercepts a message or password, not knowing the key and tries every single combination. This is easy with the caesar cipher since there are only all the letters in the alphabet. The more complex the cipher, the larger amount of time it will take to do brute force

Ex: Say we have a 5 letter alphabet (abcde), for simplicity and we intercepted the following message:

“dbc”

we could then just write out every combination: ecd… and so on, until we reach a combination that makes sense: “cab”

Further reading

Doctests

>>> brute_force("jFyuMy xIH'N vLONy zILwy Gy!")[20]
"Please don't brute force me!"

>>> brute_force(1)
Traceback (most recent call last):
TypeError: 'int' object is not iterable
ciphers.caesar_cipher.decrypt(input_string: str, key: int, alphabet: str | None = None) → str

decrypt

Decodes a given string of cipher-text and returns the decoded plain-text

Parameters:

  • input_string: the cipher-text that needs to be decoded

  • key: the number of letters to shift the message backwards by to decode

Optional: * alphabet (None): the alphabet used to decode the cipher, if not

specified, the standard english alphabet with upper and lowercase letters is used

Returns: * A string containing the decoded plain-text

More on the caesar cipher

The caesar cipher is named after Julius Caesar who used it when sending secret military messages to his troops. This is a simple substitution cipher where very character in the plain-text is shifted by a certain number known as the “key” or “shift”. Please keep in mind, here we will be focused on decryption.

Example: Say we have the following cipher-text: “Jgnnq, ecrvckp”

And our alphabet is made up of lower and uppercase letters: “abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ”

And our shift is “2”

To decode the message, we would do the same thing as encoding, but in reverse. The first letter, “J” would become “H” (remember: we are decoding) because “H” is two letters in reverse (to the left) of “J”. We would continue doing this. A letter like “a” would shift back to the end of the alphabet, and would become “Z” or “Y” and so on.

Our final message would be “Hello, captain”

Further reading

Doctests

>>> decrypt('bpm yCqks jzwEv nwF rCuxA wDmz Bpm tiHG lwo', 8)
'The quick brown fox jumps over the lazy dog'

>>> decrypt('s nWjq dSjYW cWq', 8000)
'A very large key'

>>> decrypt('f qtbjwhfxj fqumfgjy', 5, 'abcdefghijklmnopqrstuvwxyz')
'a lowercase alphabet'
ciphers.caesar_cipher.encrypt(input_string: str, key: int, alphabet: str | None = None) → str

encrypt

Encodes a given string with the caesar cipher and returns the encoded message

Parameters:

  • input_string: the plain-text that needs to be encoded

  • key: the number of letters to shift the message by

Optional: * alphabet (None): the alphabet used to encode the cipher, if not

specified, the standard english alphabet with upper and lowercase letters is used

Returns: * A string containing the encoded cipher-text

More on the caesar cipher

The caesar cipher is named after Julius Caesar who used it when sending secret military messages to his troops. This is a simple substitution cipher where every character in the plain-text is shifted by a certain number known as the “key” or “shift”.

Example: Say we have the following message: “Hello, captain”

And our alphabet is made up of lower and uppercase letters: “abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ”

And our shift is “2”

We can then encode the message, one letter at a time. “H” would become “J”, since “J” is two letters away, and so on. If the shift is ever two large, or our letter is at the end of the alphabet, we just start at the beginning (“Z” would shift to “a” then “b” and so on).

Our final message would be “Jgnnq, ecrvckp”

Further reading

Doctests

>>> encrypt('The quick brown fox jumps over the lazy dog', 8)
'bpm yCqks jzwEv nwF rCuxA wDmz Bpm tiHG lwo'

>>> encrypt('A very large key', 8000)
's nWjq dSjYW cWq'

>>> encrypt('a lowercase alphabet', 5, 'abcdefghijklmnopqrstuvwxyz')
'f qtbjwhfxj fqumfgjy'
ciphers.caesar_cipher.choice