Question

write a program for the decryption of 2-rail fence cipher. For example, the input "Cmhmtmrooeoeoorw" should return "Comehometomorrow", and input "topaesw lyr" should return "two players". in python

Answer 1

Python code for decryption of 2-rail fence cipher:

def decrypt2RailFence(cipher):

    rail = [['\n' for i in range(len(cipher))]
                  for j in range(2)]

    dir_down = None
    row, col = 0, 0

    for i in range(len(cipher)):
        if row == 0:
            dir_down = True
        if row == 1:
            dir_down = False

        rail[row][col] = '*'
        col += 1
        
        if dir_down:
            row += 1
        else:
            row -= 1
            
    index = 0
    for i in range(2):
        for j in range(len(cipher)):
            if ((rail[i][j] == '*') and
               (index < len(cipher))): 
                rail[i][j] = cipher[index]
                index += 1

    result = []
    row, col = 0, 0
    for i in range(len(cipher)):
          
        if row == 0:
            dir_down = True
        if row == 1:
            dir_down = False

        if (rail[row][col] != '*'):
            result.append(rail[row][col])
            col += 1

        if dir_down:
            row += 1
        else:
            row -= 1
    return("".join(result))
  
print(decrypt2RailFence("Cmhmtmrooeoeoorw"))
print(decrypt2RailFence("topaesw lyr"))

Sample OutPut: