scytale.ts

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import { BaseCipher } from "../base/baseCipher";
 
export class ScytaleCipher extends BaseCipher {
    readonly CipherName = "Scytale";
 
    constructor() {
        super();
    }
 
    encode(plaintext: string, diameter: number): string {
        const cols = Math.ceil(plaintext.length / diameter);
        let result = "";
 
        // Read column by column after filling the grid row by row
        for (let c = 0; c < cols; c++) {
            for (let r = 0; r < diameter; r++) {
                const index = c + r * cols;
                if (index < plaintext.length) {
                    result += plaintext[index];
                }
            }
        }
 
        return result;
    }
 
    decode(ciphertext: string, diameter: number): string {
        const cols = Math.ceil(ciphertext.length / diameter);
        const grid: string[] = Array(diameter * cols).fill("");
        let pos = 0;
 
        // Reconstruct grid in column-major order
        for (let c = 0; c < cols; c++) {
            for (let r = 0; r < diameter; r++) {
                const index = c + r * cols;
                if (pos < ciphertext.length) {
                    grid[index] = ciphertext[pos++];
                }
            }
        }
 
        // Read off row by row to recover plaintext
        return grid.join("").trimEnd();
    }
}