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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
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2 * |
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3 * LibTomCrypt is a library that provides various cryptographic |
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4 * algorithms in a highly modular and flexible manner. |
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5 * |
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6 * The library is free for all purposes without any express |
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7 * guarantee it works. |
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8 * |
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9 * Tom St Denis, [email protected], http://libtomcrypt.org |
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10 */ |
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11 #include "mycrypt.h" |
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12 |
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13 #ifdef RC4 |
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14 |
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15 const struct _prng_descriptor rc4_desc = |
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16 { |
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17 "rc4", |
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18 &rc4_start, |
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19 &rc4_add_entropy, |
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20 &rc4_ready, |
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21 &rc4_read |
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22 }; |
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23 |
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24 int rc4_start(prng_state *prng) |
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25 { |
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26 _ARGCHK(prng != NULL); |
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27 |
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28 /* set keysize to zero */ |
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29 prng->rc4.x = 0; |
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30 |
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31 return CRYPT_OK; |
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32 } |
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33 |
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34 int rc4_add_entropy(const unsigned char *buf, unsigned long len, prng_state *prng) |
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35 { |
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36 _ARGCHK(buf != NULL); |
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37 _ARGCHK(prng != NULL); |
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38 |
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39 if (prng->rc4.x + len > 256) { |
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40 return CRYPT_INVALID_KEYSIZE; |
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41 } |
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42 |
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43 while (len--) { |
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44 prng->rc4.buf[prng->rc4.x++] = *buf++; |
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45 } |
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46 |
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47 return CRYPT_OK; |
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48 |
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49 } |
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50 |
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51 int rc4_ready(prng_state *prng) |
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52 { |
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53 unsigned char key[256], tmp; |
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54 int keylen, x, y; |
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55 |
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56 _ARGCHK(prng != NULL); |
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57 |
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58 /* extract the key */ |
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59 memcpy(key, prng->rc4.buf, 256); |
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60 keylen = prng->rc4.x; |
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61 |
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62 /* make RC4 perm and shuffle */ |
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63 for (x = 0; x < 256; x++) { |
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64 prng->rc4.buf[x] = x; |
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65 } |
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66 |
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67 for (x = y = 0; x < 256; x++) { |
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68 y = (y + prng->rc4.buf[x] + key[x % keylen]) & 255; |
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69 tmp = prng->rc4.buf[x]; prng->rc4.buf[x] = prng->rc4.buf[y]; prng->rc4.buf[y] = tmp; |
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70 } |
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71 prng->rc4.x = x; |
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72 prng->rc4.y = y; |
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73 |
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74 #ifdef CLEAN_STACK |
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75 zeromem(key, sizeof(key)); |
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76 #endif |
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77 |
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78 return CRYPT_OK; |
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79 } |
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80 |
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81 unsigned long rc4_read(unsigned char *buf, unsigned long len, prng_state *prng) |
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82 { |
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83 int x, y; |
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84 unsigned char *s, tmp; |
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85 unsigned long n; |
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86 |
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87 _ARGCHK(buf != NULL); |
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88 _ARGCHK(prng != NULL); |
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89 |
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90 n = len; |
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91 x = prng->rc4.x; |
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92 y = prng->rc4.y; |
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93 s = prng->rc4.buf; |
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94 while (len--) { |
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95 x = (x + 1) & 255; |
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96 y = (y + s[x]) & 255; |
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97 tmp = s[x]; s[x] = s[y]; s[y] = tmp; |
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98 tmp = (s[x] + s[y]) & 255; |
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99 *buf++ ^= s[tmp]; |
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100 } |
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101 prng->rc4.x = x; |
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102 prng->rc4.y = y; |
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103 return n; |
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104 } |
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105 |
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106 #endif |
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107 |
