Rosetta Code

Vigenère cipher

Encode and decode a short uppercase message with a fixed Vigenère key.

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Sourcerosettacode/popular/vigen_re_cipher.vibe
def alphabet -> string
  "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
end

def shift_char(char: string, key_char: string, direction: string) -> string
  char_index = alphabet.index(char)
  key_index = alphabet.index(key_char)
  raise ArgumentError, "expected uppercase letters" if char_index == nil || key_index == nil

  if direction == "encode"
    alphabet.chars.fetch((char_index + key_index) % 26)
  else
    alphabet.chars.fetch((char_index - key_index + 26) % 26)
  end
end

def apply_vigenere(text: string, key: string, direction: string) -> string
  text_chars = text.chars
  key_chars = key.chars
  output = ""
  key_index = 0
  index = 0

  while index < text.length
    char = text_chars.fetch(index)
    if char == " "
      output = output + char
    else
      output = output + shift_char(char, key_chars.fetch(key_index % key.length), direction)
      key_index = key_index + 1
    end
    index = index + 1
  end

  output
end

def run -> { decoded: string, encoded: string }
  plain = "VIBESCRIPT ROCKS"
  key = "CODE"
  encoded = apply_vigenere(plain, key, "encode")
  {
    encoded: encoded,
    decoded: apply_vigenere(encoded, key, "decode")
  }
end

Output

Click Run example to see the result.

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