rc4.c 2.6 KB

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  1. /*
  2. * Copyright (c) 2007, Cameron Rich
  3. *
  4. * All rights reserved.
  5. *
  6. * Redistribution and use in source and binary forms, with or without
  7. * modification, are permitted provided that the following conditions are met:
  8. *
  9. * * Redistributions of source code must retain the above copyright notice,
  10. * this list of conditions and the following disclaimer.
  11. * * Redistributions in binary form must reproduce the above copyright notice,
  12. * this list of conditions and the following disclaimer in the documentation
  13. * and/or other materials provided with the distribution.
  14. * * Neither the name of the axTLS project nor the names of its contributors
  15. * may be used to endorse or promote products derived from this software
  16. * without specific prior written permission.
  17. *
  18. * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  19. * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  20. * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  21. * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  22. * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  23. * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  24. * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  25. * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  26. * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  27. * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  28. * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29. */
  30. /**
  31. * An implementation of the RC4/ARC4 algorithm.
  32. * Originally written by Christophe Devine.
  33. */
  34. #include <string.h>
  35. #include "crypto.h"
  36. /**
  37. * Get ready for an encrypt/decrypt operation
  38. */
  39. void RC4_setup(RC4_CTX *ctx, const uint8_t *key, int length)
  40. {
  41. int i, j = 0, k = 0, a;
  42. uint8_t *m;
  43. ctx->x = 0;
  44. ctx->y = 0;
  45. m = ctx->m;
  46. for (i = 0; i < 256; i++)
  47. m[i] = i;
  48. for (i = 0; i < 256; i++)
  49. {
  50. a = m[i];
  51. j = (uint8_t)(j + a + key[k]);
  52. m[i] = m[j];
  53. m[j] = a;
  54. if (++k >= length)
  55. k = 0;
  56. }
  57. }
  58. /**
  59. * Perform the encrypt/decrypt operation (can use it for either since
  60. * this is a stream cipher).
  61. */
  62. void RC4_crypt(RC4_CTX *ctx, const uint8_t *msg, uint8_t *out, int length)
  63. {
  64. int i;
  65. uint8_t *m, x, y, a, b;
  66. out = (uint8_t *)msg;
  67. x = ctx->x;
  68. y = ctx->y;
  69. m = ctx->m;
  70. for (i = 0; i < length; i++)
  71. {
  72. a = m[++x];
  73. y += a;
  74. m[x] = b = m[y];
  75. m[y] = a;
  76. out[i] ^= m[(uint8_t)(a + b)];
  77. }
  78. ctx->x = x;
  79. ctx->y = y;
  80. }