Stream cipher (sequence cipher) and RC4 algorithm

"stream cipher (sequence cipher) and RC4 algorithm"

RC4 is a sequence cipher, which is a variable key length, byte-oriented sequence cipher, a plaintext byte that differs from a key byte, or produces a secret text section.

algorithm principle: for n = 8 bit long words, that is, in one byte, at this time n = 256, with a variable length key from 1 to 256 bytes to initialize a 256-byte state vector arr,arr element arr[0],arr[1],,,arr[255], Arr from start to finish contains all 8 bits of 0~255, key key in the key stream is selected by 256 elements in ARR to act as a certain way; the elements in Arr are replaced once for each key value generated.

Initialization

Initialize the element in arr to arr[0] = 0,arr[1] = 1,,,,, arr[255] = 255, the length of the key is Len, and for each element in arr, the element in the arr[i] is replaced by the key K, Because only the elements in the array are in a disordered arrangement, the array arr also contains 0~255 elements.

Initializes the core code for (int i = 0; i < i++) {Arr[i] = i;     K[i] = key[i% len];     The K array is a loop of the elements in the key in the array}//The data in the array is arranged in a disordered order for (int i = 0; i < i++) {j = (j + arr[i] + k[i])% 256;     TMP = Arr[i];     Arr[i] = Arr[j]; ARR[J] = tmp; }

when encrypting, the input plaintext is different from the key or, when decrypted, the ciphertext is different from the key.

The core code for encryption and decryption for (size_t j = 0; J < Len; J + +) {x = (x + 1)% 256;          y = (y + arr[x])% 256;     TMP = arr[x];     ARR[X] = Arr[y];          Arr[y] = tmp;     T = (Arr[x] + arr[y])% 256; PTR[J] ^= arr[t]; }

The following is the complete program:

Header file "stream.h" #pragma  once//sequence password (stream password) #include &NBSP;&LT;STRING.H&GT;VOID&NBSP;RC4 (char* arr,  Char* ptr, size_t len)        //to encrypt or decrypt, arr is the key, PTR is plaintext {     int x = -1;    int y = 0;     int t = 0;    char tmp = 0;     for  (size_t j = 0; j < len; j++)    {        x =  (x + 1)  % 256;        y =  (Y + arr[x])  % 256;        tmp = arr[x];       arr[x] = arr[y];        arr[y] = tmp;       t =  ( Arr[x] + arr[y])  % 256;       ptr[j] ^= arr[t];    }} Void init (Char *arr, char* key, size_t len)      //initialization key , (Key scheduling algorithm KSA) {    int j = 0;    char k[256] =  { 0 };    char tmp = 0;    for  ( int i = 0; i < 256; i++)     {        arr[i] = i;       k[i] = key[i The  % len];       //k array is a loop of elements in a key in an array       } //the data in the array in a disordered arrangement     for  (int i = 0; i <  256; i++)     {       j =  (j +  Arr[i] + k[i])  % 256;       tmp = arr[i];        arr[i] = arr[j];       arr[j] = tmp;     }}void menu (char *arr, char* key, char* ptr)      //main Menu {    char n, ch;    char arr1[256]  = { 0 };    printf ("**********************************\n");     printf ("*********&NBSP;&NBSP;--RC4 algorithm    *********\n");     printf ("*********  1. Encryption and decryption   *********\n");     printf ("*********   0. Exit         *********\n ");     printf (" ****** \ n ");     printf ("---Please select: "); &NBSP;&NBSP;&NBSP;&NBSP;SCANF ("%c ", &NBSP;&AMP;N);     switch  (n)     {     case  ' 1 ':          printf ("Please enter plaintext that needs to be encrypted:");          fflush (stdin);          //Clear Buffer           for  (int i = 0; i < 256; i++)         {             if  ((Ch = getchar ())  !=  ' \ n ')             {                ptr[i] = ch;            }             else            {               break;            }        }         init (Arr, key, strlen (key));         for  (int i = 0; i < 256; i++)            //Saving the initialized arr       {            arr1[i] = arr[i];         }               &NBSP;&NBSP;RC4 (Arr, ptr, strlen (PTR));        //Encryption          printf ("\ n output ciphertext:");         printf ("%s",  ptr);  &nbSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;RC4 (Arr1, ptr,  strlen (PTR))      //decrypt         printf ("\ n the output of the plaintext is: ");         printf ("%s ",  ptr);         break;    case  ' 0 ':         exit (exit_failure);     default:        break ;     }}

Source Files Stream.cpp#define _crt_secure_no_warnings 1#include <stdio.h> #include <stdlib.h> #include "stream.h    "Int main () {char arr[256] = {0};    Char key[256] = {"Zheshiyigemiyao"};     Char ptr[256] = {0};     Menu (arr, key, PTR);    System ("pause"); return 0;}

This article from "Unintentional persistent" blog, declined reprint!

Stream cipher (sequence cipher) and RC4 algorithm