Module: Transposition

Defined in:
lib/dekryptos/transposition.rb

Overview

Encryption/decryption using keyed columnar transposition (en.wikipedia.org/wiki/Transposition_cipher)

Instance Method Summary collapse

Instance Method Details

#decrypt(ciphertext, width) ⇒ Object

Public: decrypts text via keyed columnar transposition.

The decryption method converts the ciphertext to an array, each row within which comprises width characters. Each row in the array is reversed and the entire array is transposed, after which the array is converted back to a string.

Parameter(s)

ciphertext - String: the text to be decrypted. width - Integer: the width of each row in the intermediary table required for transposition.

Return Value

String: the decrypted text.

Example

Assuming K3 is part 3 of the Kryptos sculpture: decrypt(decrypt(K3, 4), 48) => # Results in the plaintext



59
60
61
62
63
64
65
66
 
# File 'lib/dekryptos/transposition.rb', line 59

def decrypt(ciphertext, width)
  matrix = ciphertext.chars.each_slice(width).map(&:join)
  matrix.each_with_index do |_, index|
    matrix[index] = matrix[index].split('')
  end

  matrix.map(&:reverse).transpose.join('')
end

#encrypt(plaintext, width) ⇒ Object

Public: encrypts text via keyed columnar transposition.

The encryption method converts the plaintext to an array, each row within which comprises width characters. The array is then transposed and each row is reversed, after which the array is converted back to a string.

Parameter(s)

plaintext - String: the text to be encrypted. width - Integer: the width of each row in the intermediary table required for transposition.

Return Value

String: the encrypted text.

Example

Assuming pt is the plaintext version of K3: encrypt(encrypt(pt, 7), 84) => # Results in K3



30
31
32
33
34
35
36
37
 
# File 'lib/dekryptos/transposition.rb', line 30

def encrypt(plaintext, width)
  matrix = plaintext.chars.each_slice(width).map(&:join)
  matrix.each_with_index do |_, index|
    matrix[index] = matrix[index].split('')
  end

  matrix.transpose.map(&:reverse).join('')
end