1 /* 2 * RC4 stream cipher 3 * Copyright (c) 2002-2005, Jouni Malinen <j (at) w1.fi> 4 * 5 * This software may be distributed under the terms of the BSD license. 6 * See README for more details. 7 */ 8 9 #include "includes.h" 10 11 #include "common.h" 12 #include "crypto.h" 13 14 #define S_SWAP(a,b) do { u8 t = S[a]; S[a] = S[b]; S[b] = t; } while(0) 15 16 int rc4_skip(const u8 *key, size_t keylen, size_t skip, 17 u8 *data, size_t data_len) 18 { 19 u32 i, j, k; 20 u8 S[256], *pos; 21 size_t kpos; 22 23 /* Setup RC4 state */ 24 for (i = 0; i < 256; i++) 25 S[i] = i; 26 j = 0; 27 kpos = 0; 28 for (i = 0; i < 256; i++) { 29 j = (j + S[i] + key[kpos]) & 0xff; 30 kpos++; 31 if (kpos >= keylen) 32 kpos = 0; 33 S_SWAP(i, j); 34 } 35 36 /* Skip the start of the stream */ 37 i = j = 0; 38 for (k = 0; k < skip; k++) { 39 i = (i + 1) & 0xff; 40 j = (j + S[i]) & 0xff; 41 S_SWAP(i, j); 42 } 43 44 /* Apply RC4 to data */ 45 pos = data; 46 for (k = 0; k < data_len; k++) { 47 i = (i + 1) & 0xff; 48 j = (j + S[i]) & 0xff; 49 S_SWAP(i, j); 50 *pos++ ^= S[(S[i] + S[j]) & 0xff]; 51 } 52 53 return 0; 54 } 55
