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annotate rc4.c @ 0:d7da3b1e1540 libtomcrypt

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put back the 0.95 makefile which was inadvertently merged over
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:21:40 +0000
parents
children 5d99163f7e32
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d7da3b1e1540 put back the 0.95 makefile which was inadvertently merged over
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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