信息安全，Cryptography密码学

假设我们要使用带加密密钥3的铁路围栏密码解密消息“daxsarineaistestsmoy”。请显示您如何继续操作的步骤。

drtiansexamissoeasy

# Python3 program to illustrate
# Rail Fence Cipher Encryption
# and Decryption

# function to encrypt a message
def encryptRailFence(text, key):

    # create the matrix to cipher
    # plain text key = rows ,
    # length(text) = columns
    # filling the rail matrix
    # to distinguish filled
    # spaces from blank ones
    rail = [['\n' for i in range(len(text))]
            for j in range(key)]

    # to find the direction
    dir_down = False
    row, col = 0, 0

    for i in range(len(text)):

        # check the direction of flow
        # reverse the direction if we've just
        # filled the top or bottom rail
        if (row == 0) or (row == key - 1):
            dir_down = not dir_down

        # fill the corresponding alphabet
        rail[row][col] = text[i]
        col += 1

        # find the next row using
        # direction flag
        if dir_down:
            row += 1
        else:
            row -= 1
    # now we can construct the cipher
    # using the rail matrix
    result = []
    for i in range(key):
        for j in range(len(text)):
            if rail[i][j] != '\n':
                result.append(rail[i][j])
    return("" . join(result))

# This function receives cipher-text
# and key and returns the original
# text after decryption
def decryptRailFence(cipher, key):

    # create the matrix to cipher
    # plain text key = rows ,
    # length(text) = columns
    # filling the rail matrix to
    # distinguish filled spaces
    # from blank ones
    rail = [['\n' for i in range(len(cipher))]
            for j in range(key)]

    # to find the direction
    dir_down = None
    row, col = 0, 0

    # mark the places with '*'
    for i in range(len(cipher)):
        if row == 0:
            dir_down = True
        if row == key - 1:
            dir_down = False

        # place the marker
        rail[row][col] = '*'
        col += 1

        # find the next row
        # using direction flag
        if dir_down:
            row += 1
        else:
            row -= 1

    # now we can construct the
    # fill the rail matrix
    index = 0
    for i in range(key):
        for j in range(len(cipher)):
            if ((rail[i][j] == '*') and
                    (index < len(cipher))):
                rail[i][j] = cipher[index]
                index += 1

    # now read the matrix in
    # zig-zag manner to construct
    # the resultant text
    result = []
    row, col = 0, 0
    for i in range(len(cipher)):

        # check the direction of flow
        if row == 0:
            dir_down = True
        if row == key-1:
            dir_down = False

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

        # find the next row using
        # direction flag
        if dir_down:
            row += 1
        else:
            row -= 1
    return("".join(result))

# Driver code
if __name__ == "__main__":
    print(decryptRailFence("daxsarineaisestsmoy", 3))