annotate libtomcrypt/src/encauth/ccm/ccm_add_nonce.c @ 1715:3974f087d9c0

Disallow leading lines before the ident for server (#102) Per RFC4253 4.2 clients must be able to process other lines of data before the version string, server behavior is not defined neither with MUST/SHOULD nor with MAY. If server process up to 50 lines too - it may cause too long hanging session with invalid/evil client that consume host resources and potentially may lead to DDoS on poor embedded boxes. Let's require first line from client to be version string and fail early if it's not - matches both RFC and real OpenSSH behavior.
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Mon, 15 Jun 2020 18:22:18 +0500
parents 6dba84798cd5
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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 #include "tomcrypt.h"
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10
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11 #ifdef LTC_CCM_MODE
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12
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13 /**
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14 Add nonce data to the CCM state
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15 @param ccm The CCM state
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16 @param nonce The nonce data to add
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17 @param noncelen The length of the nonce
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18 @return CRYPT_OK on success
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19 */
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20 int ccm_add_nonce(ccm_state *ccm,
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21 const unsigned char *nonce, unsigned long noncelen)
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22 {
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23 unsigned long x, y, len;
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24 int err;
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25
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26 LTC_ARGCHK(ccm != NULL);
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27 LTC_ARGCHK(nonce != NULL);
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28
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29 /* increase L to match the nonce len */
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30 ccm->noncelen = (noncelen > 13) ? 13 : noncelen;
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31 if ((15 - ccm->noncelen) > ccm->L) {
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32 ccm->L = 15 - ccm->noncelen;
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33 }
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34
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35 /* decrease noncelen to match L */
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36 if ((ccm->noncelen + ccm->L) > 15) {
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37 ccm->noncelen = 15 - ccm->L;
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38 }
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39
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40 /* form B_0 == flags | Nonce N | l(m) */
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41 x = 0;
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42 ccm->PAD[x++] = (unsigned char)(((ccm->aadlen > 0) ? (1<<6) : 0) |
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43 (((ccm->taglen - 2)>>1)<<3) |
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44 (ccm->L-1));
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45
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46 /* nonce */
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47 for (y = 0; y < (16 - (ccm->L + 1)); y++) {
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48 ccm->PAD[x++] = nonce[y];
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49 }
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50
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51 /* store len */
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52 len = ccm->ptlen;
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53
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54 /* shift len so the upper bytes of len are the contents of the length */
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55 for (y = ccm->L; y < 4; y++) {
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56 len <<= 8;
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57 }
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58
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59 /* store l(m) (only store 32-bits) */
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60 for (y = 0; ccm->L > 4 && (ccm->L-y)>4; y++) {
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61 ccm->PAD[x++] = 0;
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62 }
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63 for (; y < ccm->L; y++) {
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64 ccm->PAD[x++] = (unsigned char)((len >> 24) & 255);
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65 len <<= 8;
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66 }
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67
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68 /* encrypt PAD */
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69 if ((err = cipher_descriptor[ccm->cipher].ecb_encrypt(ccm->PAD, ccm->PAD, &ccm->K)) != CRYPT_OK) {
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70 return err;
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71 }
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72
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73 /* handle header */
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74 ccm->x = 0;
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75 if (ccm->aadlen > 0) {
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76 /* store length */
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77 if (ccm->aadlen < ((1UL<<16) - (1UL<<8))) {
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78 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>8) & 255;
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79 ccm->PAD[ccm->x++] ^= ccm->aadlen & 255;
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80 } else {
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81 ccm->PAD[ccm->x++] ^= 0xFF;
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82 ccm->PAD[ccm->x++] ^= 0xFE;
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83 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>24) & 255;
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84 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>16) & 255;
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85 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>8) & 255;
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86 ccm->PAD[ccm->x++] ^= ccm->aadlen & 255;
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87 }
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88 }
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89
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90 /* setup the ctr counter */
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91 x = 0;
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92
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93 /* flags */
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94 ccm->ctr[x++] = (unsigned char)ccm->L-1;
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95
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96 /* nonce */
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97 for (y = 0; y < (16 - (ccm->L+1)); ++y) {
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98 ccm->ctr[x++] = nonce[y];
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99 }
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100 /* offset */
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101 while (x < 16) {
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102 ccm->ctr[x++] = 0;
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103 }
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104
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105 ccm->CTRlen = 16;
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106 return CRYPT_OK;
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107 }
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108
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109 #endif
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110
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111 /* ref: $Format:%D$ */
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112 /* git commit: $Format:%H$ */
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113 /* commit time: $Format:%ai$ */