Editing Rail fence cipher (section)

==Cryptanalysis==
The cipher's key is <math>N</math>, the number of rails. If <math>N</math> is known, the ciphertext can be decrypted by using the above algorithm. Values of <math>N</math> equal to or greater than <math>L</math>, the length of the ciphertext, are not usable, since then the ciphertext is the same as the plaintext. Therefore the number of usable keys is low, allowing the brute-force attack of trying all possible keys. As a result, the rail-fence cipher is considered weak.{{cn|date=May 2021}}