Mercurial > dropbear

annotate libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c @ 1715:3974f087d9c0

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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
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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 /**
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12 @file der_length_integer.c
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13 ASN.1 DER, get length of encoding, Tom St Denis
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14 */
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17 #ifdef LTC_DER
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18 /**
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19 Gets length of DER encoding of num
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20 @param num The int to get the size of
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21 @param outlen [out] The length of the DER encoding for the given integer
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22 @return CRYPT_OK if successful
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23 */
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24 int der_length_integer(void *num, unsigned long *outlen)
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25 {
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26 unsigned long z, len;
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27 int leading_zero;
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28
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29 LTC_ARGCHK(num != NULL);
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30 LTC_ARGCHK(outlen != NULL);
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31
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32 if (mp_cmp_d(num, 0) != LTC_MP_LT) {
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33 /* positive */
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34
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35 /* we only need a leading zero if the msb of the first byte is one */
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36 if ((mp_count_bits(num) & 7) == 0 || mp_iszero(num) == LTC_MP_YES) {
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37 leading_zero = 1;
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38 } else {
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39 leading_zero = 0;
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40 }
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42 /* size for bignum */
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43 z = len = leading_zero + mp_unsigned_bin_size(num);
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44 } else {
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45 /* it's negative */
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46 /* find power of 2 that is a multiple of eight and greater than count bits */
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47 z = mp_count_bits(num);
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48 z = z + (8 - (z & 7));
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49 if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) --z;
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50 len = z = z >> 3;
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51 }
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52
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53 /* now we need a length */
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54 if (z < 128) {
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55 /* short form */
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56 ++len;
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57 } else {
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58 /* long form (relies on z != 0), assumes length bytes < 128 */
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59 ++len;
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60
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61 while (z) {
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62 ++len;
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63 z >>= 8;
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64 }
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65 }
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66
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67 /* we need a 0x02 to indicate it's INTEGER */
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68 ++len;
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69
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70 /* return length */
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71 *outlen = len;
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72 return CRYPT_OK;
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73 }
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75 #endif
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76
1471
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77 /* ref: $Format:%D$ */
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78 /* git commit: $Format:%H$ */
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79 /* commit time: $Format:%ai$ */