view libtomcrypt/src/pk/asn1/der/ia5/der_length_ia5_string.c @ 1790:42745af83b7d

Introduce extra delay before closing unauthenticated sessions To make it harder for attackers, introduce a delay to keep an unauthenticated session open a bit longer, thus blocking a connection slot until after the delay. Without this, while there is a limit on the amount of attempts an attacker can make at the same time (MAX_UNAUTH_PER_IP), the time taken by dropbear to handle one attempt is still short and thus for each of the allowed parallel attempts many attempts can be chained one after the other. The attempt rate is then: "MAX_UNAUTH_PER_IP / <process time of one attempt>". With the delay, this rate becomes: "MAX_UNAUTH_PER_IP / UNAUTH_CLOSE_DELAY".
author Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
date Wed, 15 Feb 2017 13:53:04 +0100
parents 6dba84798cd5
children
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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 */
#include "tomcrypt.h"

/**
  @file der_length_ia5_string.c
  ASN.1 DER, get length of IA5 STRING, Tom St Denis
*/

#ifdef LTC_DER

static const struct {
   int code, value;
} ia5_table[] = {
{ '\0', 0 },
{ '\a', 7 },
{ '\b', 8 },
{ '\t', 9 },
{ '\n', 10 },
{ '\f', 12 },
{ '\r', 13 },
{ ' ', 32 },
{ '!', 33 },
{ '"', 34 },
{ '#', 35 },
{ '$', 36 },
{ '%', 37 },
{ '&', 38 },
{ '\'', 39 },
{ '(', 40 },
{ ')', 41 },
{ '*', 42 },
{ '+', 43 },
{ ',', 44 },
{ '-', 45 },
{ '.', 46 },
{ '/', 47 },
{ '0', 48 },
{ '1', 49 },
{ '2', 50 },
{ '3', 51 },
{ '4', 52 },
{ '5', 53 },
{ '6', 54 },
{ '7', 55 },
{ '8', 56 },
{ '9', 57 },
{ ':', 58 },
{ ';', 59 },
{ '<', 60 },
{ '=', 61 },
{ '>', 62 },
{ '?', 63 },
{ '@', 64 },
{ 'A', 65 },
{ 'B', 66 },
{ 'C', 67 },
{ 'D', 68 },
{ 'E', 69 },
{ 'F', 70 },
{ 'G', 71 },
{ 'H', 72 },
{ 'I', 73 },
{ 'J', 74 },
{ 'K', 75 },
{ 'L', 76 },
{ 'M', 77 },
{ 'N', 78 },
{ 'O', 79 },
{ 'P', 80 },
{ 'Q', 81 },
{ 'R', 82 },
{ 'S', 83 },
{ 'T', 84 },
{ 'U', 85 },
{ 'V', 86 },
{ 'W', 87 },
{ 'X', 88 },
{ 'Y', 89 },
{ 'Z', 90 },
{ '[', 91 },
{ '\\', 92 },
{ ']', 93 },
{ '^', 94 },
{ '_', 95 },
{ '`', 96 },
{ 'a', 97 },
{ 'b', 98 },
{ 'c', 99 },
{ 'd', 100 },
{ 'e', 101 },
{ 'f', 102 },
{ 'g', 103 },
{ 'h', 104 },
{ 'i', 105 },
{ 'j', 106 },
{ 'k', 107 },
{ 'l', 108 },
{ 'm', 109 },
{ 'n', 110 },
{ 'o', 111 },
{ 'p', 112 },
{ 'q', 113 },
{ 'r', 114 },
{ 's', 115 },
{ 't', 116 },
{ 'u', 117 },
{ 'v', 118 },
{ 'w', 119 },
{ 'x', 120 },
{ 'y', 121 },
{ 'z', 122 },
{ '{', 123 },
{ '|', 124 },
{ '}', 125 },
{ '~', 126 }
};

int der_ia5_char_encode(int c)
{
   int x;
   for (x = 0; x < (int)(sizeof(ia5_table)/sizeof(ia5_table[0])); x++) {
       if (ia5_table[x].code == c) {
          return ia5_table[x].value;
       }
   }
   return -1;
}

int der_ia5_value_decode(int v)
{
   int x;
   for (x = 0; x < (int)(sizeof(ia5_table)/sizeof(ia5_table[0])); x++) {
       if (ia5_table[x].value == v) {
          return ia5_table[x].code;
       }
   }
   return -1;
}

/**
  Gets length of DER encoding of IA5 STRING
  @param octets   The values you want to encode
  @param noctets  The number of octets in the string to encode
  @param outlen   [out] The length of the DER encoding for the given string
  @return CRYPT_OK if successful
*/
int der_length_ia5_string(const unsigned char *octets, unsigned long noctets, unsigned long *outlen)
{
   unsigned long x;

   LTC_ARGCHK(outlen != NULL);
   LTC_ARGCHK(octets != NULL);

   /* scan string for validity */
   for (x = 0; x < noctets; x++) {
       if (der_ia5_char_encode(octets[x]) == -1) {
          return CRYPT_INVALID_ARG;
       }
   }

   if (noctets < 128) {
      /* 16 LL DD DD DD ... */
      *outlen = 2 + noctets;
   } else if (noctets < 256) {
      /* 16 81 LL DD DD DD ... */
      *outlen = 3 + noctets;
   } else if (noctets < 65536UL) {
      /* 16 82 LL LL DD DD DD ... */
      *outlen = 4 + noctets;
   } else if (noctets < 16777216UL) {
      /* 16 83 LL LL LL DD DD DD ... */
      *outlen = 5 + noctets;
   } else {
      return CRYPT_INVALID_ARG;
   }

   return CRYPT_OK;
}

#endif


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