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rc4.c
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rc4.c
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#include "rc4.h"
void rc4_init(rc4_state_t *state, const unsigned char *key, unsigned int keylen)
{
unsigned char j;
unsigned char tmp;
int i;
for (i = 0; i < 256; i++)
state->buffer[i] = i;
state->x = 0;
state->y = 0;
if (keylen > 0) { /* 0 modulo 0 is undefined anyway. */
for (i = j = 0; i < 256; i++) {
j += state->buffer[i] + key[i%keylen];
tmp = state->buffer[i];
state->buffer[i] = state->buffer[j];
state->buffer[j] = tmp;
}
}
}
void rc4_encrypt(rc4_state_t *state, const unsigned char *in, unsigned char *out, unsigned long len)
{
unsigned char x, y;
unsigned char tmp;
unsigned char k; /* Keystream. */
unsigned long i;
x = state->x;
y = state->y;
for (i = 0; i < len; i++) {
x++;
y += state->buffer[x];
tmp = state->buffer[x];
state->buffer[x] = state->buffer[y];
state->buffer[y] = tmp;
k = state->buffer[(state->buffer[x] + state->buffer[y]) & 0xff];
out[i] = in[i] ^ k;
}
state->x = x;
state->y = y;
}
void rc4_encrypt_skip(rc4_state_t *state, const unsigned char *in, unsigned char *out, unsigned long len, unsigned long skip)
{
unsigned char x, y;
unsigned char tmp;
unsigned char k; /* Keystream. */
unsigned long i;
x = state->x;
y = state->y;
for (i = 0; i < skip; i++) {
x++;
y += state->buffer[x];
tmp = state->buffer[x];
state->buffer[x] = state->buffer[y];
state->buffer[y] = tmp;
}
for (i = 0; i < len; i++) {
x++;
y += state->buffer[x];
tmp = state->buffer[x];
state->buffer[x] = state->buffer[y];
state->buffer[y] = tmp;
k= state->buffer[(state->buffer[x] + state->buffer[y]) & 0xff];
out[i] = in[i] ^ k;
}
state->x = x;
state->y = y;
}