Quick lune script to brute force case cipher encoded texts

brutus.luau

--> Brute forces some caesar cipher encoded text

local process = require("@lune/process")
local stdio = require("@lune/stdio")
local net = require("@lune/net")

local CHARS = ("abcdefghijklmnopqrstuvwxyz"):split("")

print(`brutus.luau: {process.os}-{process.arch}`)
local ciphertext = process.args[1] or error("usage: ./brutus.luau [CIPHERTEXT]")
local ciphertextChars = ciphertext:split("")

local possiblePlaintexts = {}

for offset = 1, #CHARS do
	local shifted = ""

	for _, char in ciphertextChars do
		-- Our alphabet set is lowercase, so we normalize the input
		char = string.lower(char)

		-- Check if the character is in our alphabet, if not, we ignore it
		local alphabetPos = table.find(CHARS, char)
		if not alphabetPos then
			shifted ..= char
			continue
		end

		-- Shift the character based on current offset
		local shiftedPos = alphabetPos + offset
		if shiftedPos > #CHARS then
			-- Wrap back to beginning it exceeds the length of the alphabet
			shiftedPos = shiftedPos - #CHARS
		end

		-- Get the character at the shifted position, at push to str
		local shiftedChar = CHARS[shiftedPos]
		shifted ..= shiftedChar
	end

	table.insert(possiblePlaintexts, shifted)
end

local toFilter: boolean = stdio.prompt("confirm", "Filter plaintexts that are not in the English dictionary?")

if toFilter then
    local filteredPlaintexts = {}
	for pos, possiblePlaintext in possiblePlaintexts do
		possiblePlaintext = possiblePlaintext:gsub("%p", "")
		local words = possiblePlaintext:split(" ")

		local wordValidityResults = {}
		for wordPos, word in words do
			-- One letter words are sometimes valid, but we don't include them
			local isValidWord = if #word == 1
				then false
				else net.request("https://api.dictionaryapi.dev/api/v2/entries/en/" .. word).ok
			wordValidityResults[wordPos] = isValidWord
		end

		-- If there is at least one valid English word, we consider the plaintext valid
		if table.find(wordValidityResults, true) then
			table.insert(filteredPlaintexts, possiblePlaintexts[pos])
		end
	end

    possiblePlaintexts = filteredPlaintexts
end

print("Possible plaintexts:")
print(table.concat(possiblePlaintexts, "\n"))