rc4.c 1009 B

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