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