/* LibTomCrypt, modular cryptographic library -- Tom St Denis * * LibTomCrypt is a library that provides various cryptographic * algorithms in a highly modular and flexible manner. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org */#include "mycrypt.h"#ifdef RC4const struct _prng_descriptor rc4_desc = {   "rc4",    &rc4_start,    &rc4_add_entropy,    &rc4_ready,    &rc4_read};int rc4_start(prng_state *prng){    _ARGCHK(prng != NULL);    /* set keysize to zero */    prng->rc4.x = 0;        return CRYPT_OK;}int rc4_add_entropy(const unsigned char *buf, unsigned long len, prng_state *prng){    _ARGCHK(buf != NULL);    _ARGCHK(prng != NULL);    if (prng->rc4.x + len > 256) {       return CRYPT_INVALID_KEYSIZE;    }    while (len--) {       prng->rc4.buf[prng->rc4.x++] = *buf++;    }    return CRYPT_OK;    }int rc4_ready(prng_state *prng){    unsigned char key[256], tmp;    int keylen, x, y;    _ARGCHK(prng != NULL);    /* extract the key */    memcpy(key, prng->rc4.buf, 256);    keylen = prng->rc4.x;    /* make RC4 perm and shuffle */    for (x = 0; x < 256; x++) {        prng->rc4.buf[x] = x;    }    for (x = y = 0; x < 256; x++) {        y = (y + prng->rc4.buf[x] + key[x % keylen]) & 255;        tmp = prng->rc4.buf[x]; prng->rc4.buf[x] = prng->rc4.buf[y]; prng->rc4.buf[y] = tmp;    }    prng->rc4.x = x;    prng->rc4.y = y;#ifdef CLEAN_STACK    zeromem(key, sizeof(key));#endif    return CRYPT_OK;}unsigned long rc4_read(unsigned char *buf, unsigned long len, prng_state *prng){   int x, y;    unsigned char *s, tmp;   unsigned long n;   _ARGCHK(buf != NULL);   _ARGCHK(prng != NULL);   n = len;   x = prng->rc4.x;   y = prng->rc4.y;   s = prng->rc4.buf;   while (len--) {      x = (x + 1) & 255;      y = (y + s[x]) & 255;      tmp = s[x]; s[x] = s[y]; s[y] = tmp;      tmp = (s[x] + s[y]) & 255;      *buf++ ^= s[tmp];   }   prng->rc4.x = x;   prng->rc4.y = y;   return n;}#endif