rc4.c

BLOCK加密,RC4算法,此算法简单实用, 供各网友免费学习和使用.

#include <stdio.h>

/* Prototype the encryption/decryption function     */
char *EnDeCrypt(const char *pszText, int iTextLen, const char *pszKey);
void swapints(int *array, int ndx1, int ndx2);

/* Test harness for the EnDeCrypt function below.   */
int main()
{
    char buf[256], passwd[16], *pEncrypted, *pDecrypted, *pch;
    int ix, iLen;

    for (;;)
    {
        printf("\nString to encrypt (just Enter to exit): ");
        fgets(buf, sizeof(buf), stdin);
		for (ix = strlen(buf) - 1; (ix >= 0) && (buf[ix] == 10); ix--)
			buf[ix] = 0;
        if (!buf[0])
            break;
        printf("\nKey: ");
        fgets(passwd, sizeof(passwd), stdin);
		for (ix = strlen(passwd) - 1; (ix >= 0) && (passwd[ix] == 10); ix--)
			passwd[ix] = 0;
        if (!passwd[0])
            break;
		iLen = strlen(buf);
        pEncrypted = EnDeCrypt(buf, iLen, passwd);
        printf("\nEncrypted output:\n");
        for (pch = pEncrypted, ix=0; ix < iLen; pch++, ix++)
        {
            if (!(ix % 20))
                printf("\n");
            printf("%1X ", (unsigned char)*pch);
        }
        pDecrypted = EnDeCrypt(pEncrypted, iLen, passwd);
		pDecrypted[iLen] = 0;	/* Null-terminate */
        printf("\nDecrypted text: %s", pDecrypted);
        free(pEncrypted);
        free(pDecrypted);
    }
    return 0;
}

/* :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
   ;:::                                                             :::
   ;:::  This function performs 'RC4' Stream Encryption             :::
   ;:::  (Based on what is widely thought to be RSA's RC4           :::
   ;:::  algorithm. It produces output streams that are identical   :::
   ;:::  to the commercial products)                                :::
   ;:::                                                             :::
   ;:::  Adapted by permission from a VB script by Mike Shaffer     :::
   ;:::  http://www.4guysfromrolla.com/webtech/010100-1.shtml       :::
   ;:::                                                             :::
   ;::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: */

char *EnDeCrypt(const char *pszText, int iTextLen, const char *pszKey)
/* ;:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
   ;:::  This routine does all the work. Call it both to ENcrypt    :::
   ;:::  and to DEcrypt your data.                                  :::
   ;:::  You MUST free the returned pointer when no longer needed   :::
   ;::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: */
{
    char *cipher;                       /* Output buffer                */
    int a, b, i=0, j=0, k;              /* Ambiguously named counters   */
    int ilen;                           /* Length of a string           */
    int sbox[256];                      /* Encryption array             */
    int key[256];                       /* Numeric key values           */

    ilen = strlen(pszKey);

    for (a=0; a < 256; a++)
    {
        key[a] = pszKey[a % ilen];
        sbox[a] = a;
    }

    for (a=0, b=0; a < 256; a++)
    {
        b = (b + sbox[a] + key[a]) % 256;
        swapints(sbox, a, b);
    }

    cipher = (char *)malloc(iTextLen);

    for (a=0; a < iTextLen; a++)
    {
        i = (i + 1) % 256;
        j = (j + sbox[i]) % 256;
        swapints(sbox, i, j);
        k = sbox[(sbox[i] + sbox[j]) % 256];
        cipher[a] = pszText[a] ^ k;
    }
    return cipher;
}


void swapints(int *array, int ndx1, int ndx2)
{
    int temp = array[ndx1];
    array[ndx1] = array[ndx2];
    array[ndx2] = temp;
}