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- /*
- * RC4 stream cipher
- * Copyright (c) 2002-2005, Jouni Malinen <j@w1.fi>
- *
- * This software may be distributed under the terms of the BSD license.
- * See README for more details.
- */
- #include "includes.h"
- #include "common.h"
- #include "crypto.h"
- #define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
- int rc4_skip(const u8 *key, size_t keylen, size_t skip,
- u8 *data, size_t data_len)
- {
- u32 i, j, k;
- u8 S[256], *pos;
- size_t kpos;
- /* Setup RC4 state */
- for (i = 0; i < 256; i++)
- S[i] = i;
- j = 0;
- kpos = 0;
- for (i = 0; i < 256; i++) {
- j = (j + S[i] + key[kpos]) & 0xff;
- kpos++;
- if (kpos >= keylen)
- kpos = 0;
- S_SWAP(i, j);
- }
- /* Skip the start of the stream */
- i = j = 0;
- for (k = 0; k < skip; k++) {
- i = (i + 1) & 0xff;
- j = (j + S[i]) & 0xff;
- S_SWAP(i, j);
- }
- /* Apply RC4 to data */
- pos = data;
- for (k = 0; k < data_len; k++) {
- i = (i + 1) & 0xff;
- j = (j + S[i]) & 0xff;
- S_SWAP(i, j);
- *pos++ ^= S[(S[i] + S[j]) & 0xff];
- }
- return 0;
- }
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