Scytale cipher

The ciphertext has a length $l = n \cdot m$ and can be entered in a matrix with width $m$ and height $n$ . Decryption is done by transposing the matrix (swapping rows and columns): $\text{plainText}[i * m + j] = \text{cipherText}[j * n + i]$ where $i = 0, \dots , n-1$ , $j = 0, \dots , m-1$ . By trial and error we find that $n = 7$ and $m = 6$ are the right dimensions for the matrix. The decrypted message is then

say the answer to life the universe and everything

which is obviously 42. 42 also happens to be the length of the string. The fact $6 \cdot 7 = 42$ was used for the transposition encryption.

Sample code for decryption:

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cipherText = "sattvnyanohedtyslerehtwiusvihefneenereiarg"

def scytale(text, n):
    result = ""
    for i in range(n):
        for j in range(int(len(text)/n)):
            result = result + text[n*j + i]
    return result

plainText = scytale(cipherText,7)
print(plainText)
print(len(plainText))

public class Main {

    public static void main(String []args){
        String value = "sattvnyanohedtyslerehtwiusvihefneenereiarg";
        String combine = "";
        int shift = 7;
        for (int s = 0; s < shift; s++) {
            for (int i = s; i < value.length(); i += shift) {
                combine += value.charAt(i);
            }
        }
        System.out.println(combine);
    }
}