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/* initial implementation by
* Peter White <peter@janrain.com>
*/
/* C Standard includes */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>
/* Local include */
#include "cryptonite_rc4.h"
/* Swap array elements i=State[i] and b=State[j]. */
static void swap(uint8_t *i, uint8_t *j)
{
uint8_t temp;
temp = *i;
*i = *j;
*j = temp;
}
/* Key scheduling algorithm. Swap array elements based on the key. */
void cryptonite_rc4_init(uint8_t *key, uint32_t keylen, struct rc4_ctx *ctx)
{
uint32_t i, j;
memset(ctx, 0, sizeof(struct rc4_ctx));
/* initialize context */
for (i = 0; i < 256; i++)
ctx->state[i] = i;
for (i = j = 0; i < 256; i++) {
j = (j + ctx->state[i] + key[i % keylen]) % 256;
swap(&ctx->state[i], &ctx->state[j]);
}
}
/* Combine the stream generated by the rc4 with some input */
void cryptonite_rc4_combine(struct rc4_ctx *ctx, uint8_t *input, uint32_t len, uint8_t *output)
{
uint32_t i = ctx->i;
uint32_t j = ctx->j;
uint32_t m;
uint8_t si, sj;
/* The RC4 algorithm */
for (m = 0; m < len; m++) {
i = (i + 1) & 0xff;
si = ctx->state[i];
j = (j + si) & 0xff;
sj = ctx->state[j];
/* swap(&state[i], &state[j]); */
ctx->state[i] = sj;
ctx->state[j] = si;
/* Xor the key stream value into the input */
*output++ = *input++ ^ (ctx->state[(si + sj) & 0xff]);
}
/* Output new S-box indices */
ctx->i = i;
ctx->j = j;
}
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