# 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(encryptRailFence("attack at once", 2)) 
	print(encryptRailFence("GeeksforGeeks ", 3)) 
	print(encryptRailFence("defend the east wall", 3)) 
	
	# Now decryption of the 
	# same cipher-text 
	print(decryptRailFence("anubhav awasthi", 3)) 
	print(decryptRailFence("atc toctakae", 2)) 
	print(decryptRailFence("dnhaweedtees alf tl", 3)) 

# This code is contributed 
# by anubhav awasthi