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annotate libtomcrypt/src/stream/rc4/rc4_stream.c @ 1646:6d1bbe7d5fa5 DROPBEAR_2019.77

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2019.77
author Matt Johnston <matt@ucc.asn.au>
date Sat, 23 Mar 2019 21:46:29 +0800
parents 6dba84798cd5
children
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1471
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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
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10 #include "tomcrypt.h"
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11
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12 #ifdef LTC_RC4_STREAM
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13
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14 /**
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15 Initialize an RC4 context (only the key)
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16 @param st [out] The destination of the RC4 state
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17 @param key The secret key
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18 @param keylen The length of the secret key (8 - 256 bytes)
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19 @return CRYPT_OK if successful
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20 */
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21 int rc4_stream_setup(rc4_state *st, const unsigned char *key, unsigned long keylen)
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22 {
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23 unsigned char tmp, *s;
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24 int x, y;
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25 unsigned long j;
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26
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27 LTC_ARGCHK(st != NULL);
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28 LTC_ARGCHK(key != NULL);
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29 LTC_ARGCHK(keylen >= 5); /* 40-2048 bits */
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30
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31 s = st->buf;
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32 for (x = 0; x < 256; x++) {
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33 s[x] = x;
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34 }
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35
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36 for (j = x = y = 0; x < 256; x++) {
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37 y = (y + s[x] + key[j++]) & 255;
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38 if (j == keylen) {
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39 j = 0;
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40 }
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41 tmp = s[x]; s[x] = s[y]; s[y] = tmp;
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42 }
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43 st->x = 0;
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44 st->y = 0;
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45
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46 return CRYPT_OK;
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47 }
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48
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49 /**
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50 Encrypt (or decrypt) bytes of ciphertext (or plaintext) with RC4
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51 @param st The RC4 state
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52 @param in The plaintext (or ciphertext)
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53 @param inlen The length of the input (octets)
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54 @param out [out] The ciphertext (or plaintext), length inlen
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55 @return CRYPT_OK if successful
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56 */
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57 int rc4_stream_crypt(rc4_state *st, const unsigned char *in, unsigned long inlen, unsigned char *out)
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58 {
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59 unsigned char x, y, *s, tmp;
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60
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61 LTC_ARGCHK(st != NULL);
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62 LTC_ARGCHK(in != NULL);
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63 LTC_ARGCHK(out != NULL);
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64
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65 x = st->x;
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66 y = st->y;
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67 s = st->buf;
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68 while (inlen--) {
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69 x = (x + 1) & 255;
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70 y = (y + s[x]) & 255;
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71 tmp = s[x]; s[x] = s[y]; s[y] = tmp;
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72 tmp = (s[x] + s[y]) & 255;
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73 *out++ = *in++ ^ s[tmp];
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74 }
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75 st->x = x;
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76 st->y = y;
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77 return CRYPT_OK;
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78 }
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79
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80 /**
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81 Generate a stream of random bytes via RC4
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82 @param st The RC420 state
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83 @param out [out] The output buffer
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84 @param outlen The output length
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85 @return CRYPT_OK on success
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86 */
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87 int rc4_stream_keystream(rc4_state *st, unsigned char *out, unsigned long outlen)
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88 {
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89 if (outlen == 0) return CRYPT_OK; /* nothing to do */
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90 LTC_ARGCHK(out != NULL);
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91 XMEMSET(out, 0, outlen);
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92 return rc4_stream_crypt(st, out, outlen, out);
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93 }
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94
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95 /**
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96 Terminate and clear RC4 state
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97 @param st The RC4 state
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98 @return CRYPT_OK on success
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99 */
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100 int rc4_stream_done(rc4_state *st)
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101 {
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102 LTC_ARGCHK(st != NULL);
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103 XMEMSET(st, 0, sizeof(rc4_state));
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104 return CRYPT_OK;
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105 }
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106
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107 #endif
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108
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109 /* ref: $Format:%D$ */
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110 /* git commit: $Format:%H$ */
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111 /* commit time: $Format:%ai$ */