Decryption using transposition cipher

If the encrypted message is composed of very few words 1, 2 or 3 then an anagram solver can make it possible to find them. The transposition cipher is, along with the substitution cipher, one of the most used bricks for more elaborate ciphers.

The empty squares of the grid introduce an additional difficulty, rather time-consuming, when deciphering. Because the receiver of the message must calculate the position of these, which requires among other things, to count the number of characters of the message.

If the empty boxes are not completed and the pre-calculation is not done, errors could appear in the reorganization of certain letters especially the last ones. Need Help? Message for dCode's team: Thanks to your feedback and relevant comments, dCode has developed the best 'Transposition Cipher' tool, so feel free to write! Send this message. See also: Mono-alphabetic Substitution. The message consists of the letters of the original message but in a different order.

Write a message Thanks to your feedback and relevant comments, dCode has developed the best 'Transposition Cipher' tool, so feel free to write! How to decrypt with a transposition cipher? How to recognize a transposition ciphertext? How to decipher a transposition cipher without key? What are the variants of the transposition cipher? Why completing the empty cells of the transposition table?

Even if you followed the other steps in the decryption process correctly, the plaintext would be random garbage similar to if you used the wrong key with the Caesar cipher. Enter the following code into the file editor and then save it as transpositionDecrypt.

Remember to place pyperclip. Press F5 to run the program. Transposition Cipher Decryption 2. Print with a called "pipe" character after it in case The transposition decrypt function will simulate the "columns" and First, we need to calculate a few values.

The number of "columns" in our transposition grid: The number of "rows" in our grid: The number of "shaded boxes" in the last "column" of the grid: Each string in plaintext represents a column in the grid: The column and row variables point to where in the grid the next If there are no more columns OR we're at a shaded box, go back If transpositionDecrypt.

When you run the transpositionDecrypt. If you want to decrypt a different message or use a different key, change the value assigned to the myMessage and myKey variables on lines 7 and 8. The first part of the transpositionDecrypt. The pyperclip module is imported along with another module named math on line 4. If you separate the module names with commas, you can import multiple modules with one import statement. The main function, which we start defining on line 6, creates variables named myMessage and myKey and then calls the decryption function decryptMessage.

The return value of decryptMessage is the decrypted plaintext of the ciphertext and key. This is stored in a variable named plaintext , which is printed to the screen with a pipe character at the end in case there are spaces at the end of the message and then copied to the clipboard.

The decryptMessage function follows the six decrypting steps described on page and then returns the results of decryption as a string.

The math. This happens even if the number divides evenly. For example, enter the following into the interactive shell:. If you want to round a number to the nearest integer, you can use the round function.

To see how the function works, enter the following:. If you only want to round up, you need to use the math. These functions exist in the math module, which you need to import before calling them.

Enter the following into the interactive shell:. The decryptMessage function implements each of the decryption steps as Python code. It takes an integer key and a message string as arguments. Line 25 calculates the number of columns by dividing len message by the integer in key.

This value is passed to the math. To make this program compatible with Python 2, we call float so the key becomes a floating-point value. In Python 2, the result of dividing two integers is automatically rounded down. Calling float avoids this behavior without affecting the behavior under Python 3. Line 27 calculates the number of rows, which is the integer stored in key. This value gets stored in the variable numOfRows. Line 29 calculates the number of shaded boxes in the grid, which is the number of columns times rows, minus the length of the message.

Just like the encryption program had a variable named ciphertext that was a list of strings to represent the grid of ciphertext, decryptMessage also has a list-of-strings variable named plaintext :. These strings are blank at first, with one string for each column of the grid. Using list replication, you can multiply a list of one blank string by numOfColumns to make a list of several blank strings equal to the number of columns needed.

Keep in mind that this plaintext is different from the plaintext in the main function. Remember that the grid for the 'Cenoonommstmme oo snnio. The plaintext variable will have a list of strings, and each string in the list will be a single column of this grid.

For this decryption, you want plaintext to end up with the following value:. To make the list, we first need to place each symbol in message in the correct string inside the plaintext list one at a time. Lines 36 and 37 do this:. Line 39 starts a for loop that iterates over the characters in the message string. Inside this loop, the code will adjust the column and row variables so it concatenates symbol to the correct string in the plaintext list:.

Line 40 concatenates symbol to the string at index column in the plaintext list, because each string in plaintext represents a column. Then line 41 adds 1 to column that is, it increments column so that on the next iteration of the loop, symbol will be concatenated to the next string in the plaintext list.

Boolean operators compare Boolean values or expressions that evaluate to a Boolean value and evaluate to a Boolean value. The Boolean operators and and or can help you form more complicated conditions for if and while statements. The and operator connects two expressions and evaluates to True if both expressions evaluate to True.

The or operator connects two expressions and evaluates to True if one or both expressions evaluate to True ; otherwise, these expressions evaluate to False. Enter the following into the interactive shell to see how the and operator works:. The first expression evaluates to True because the expressions on either side of the and operator both evaluate to True.

This means the expression evaluates to True and False. Because both expressions have to be True for the and operator to evaluate to True , the whole expression evaluates to False.