view libtomcrypt/src/pk/asn1/der/choice/der_decode_choice.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_decode_choice.c
  ASN.1 DER, decode a CHOICE, Tom St Denis
*/

#ifdef LTC_DER

/**
   Decode a CHOICE
   @param in       The DER encoded input
   @param inlen    [in/out] The size of the input and resulting size of read type
   @param list     The list of items to decode
   @param outlen   The number of items in the list
   @return CRYPT_OK on success
*/
int der_decode_choice(const unsigned char *in,   unsigned long *inlen,
                            ltc_asn1_list *list, unsigned long  outlen)
{
   unsigned long size, x, z;
   void          *data;

   LTC_ARGCHK(in    != NULL);
   LTC_ARGCHK(inlen != NULL);
   LTC_ARGCHK(list  != NULL);

   /* get blk size */
   if (*inlen < 2) {
      return CRYPT_INVALID_PACKET;
   }

   /* set all of the "used" flags to zero */
   for (x = 0; x < outlen; x++) {
       list[x].used = 0;
   }

   /* now scan until we have a winner */
   for (x = 0; x < outlen; x++) {
       size = list[x].size;
       data = list[x].data;

       switch (list[x].type) {
           case LTC_ASN1_BOOLEAN:
               if (der_decode_boolean(in, *inlen, data) == CRYPT_OK) {
                  if (der_length_boolean(&z) == CRYPT_OK) {
                      list[x].used = 1;
                      *inlen       = z;
                      return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_INTEGER:
               if (der_decode_integer(in, *inlen, data) == CRYPT_OK) {
                  if (der_length_integer(data, &z) == CRYPT_OK) {
                      list[x].used = 1;
                      *inlen       = z;
                      return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_SHORT_INTEGER:
               if (der_decode_short_integer(in, *inlen, data) == CRYPT_OK) {
                  if (der_length_short_integer(size, &z) == CRYPT_OK) {
                      list[x].used = 1;
                      *inlen       = z;
                      return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_BIT_STRING:
               if (der_decode_bit_string(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_bit_string(size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_RAW_BIT_STRING:
               if (der_decode_raw_bit_string(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_bit_string(size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_OCTET_STRING:
               if (der_decode_octet_string(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_octet_string(size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_NULL:
               if (*inlen == 2 && in[x] == 0x05 && in[x+1] == 0x00) {
                  *inlen = 2;
                  list[x].used   = 1;
                  return CRYPT_OK;
               }
               break;

           case LTC_ASN1_OBJECT_IDENTIFIER:
               if (der_decode_object_identifier(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_object_identifier(data, size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_TELETEX_STRING:
               if (der_decode_teletex_string(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_teletex_string(data, size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_IA5_STRING:
               if (der_decode_ia5_string(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_ia5_string(data, size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_PRINTABLE_STRING:
               if (der_decode_printable_string(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_printable_string(data, size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_UTF8_STRING:
               if (der_decode_utf8_string(in, *inlen, data, &size) == CRYPT_OK) {
                  if (der_length_utf8_string(data, size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     list[x].size = size;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_UTCTIME:
               z = *inlen;
               if (der_decode_utctime(in, &z, data) == CRYPT_OK) {
                  list[x].used = 1;
                  *inlen       = z;
                  return CRYPT_OK;
               }
               break;

           case LTC_ASN1_GENERALIZEDTIME:
               z = *inlen;
               if (der_decode_generalizedtime(in, &z, data) == CRYPT_OK) {
                  list[x].used = 1;
                  *inlen       = z;
                  return CRYPT_OK;
               }
               break;

           case LTC_ASN1_SET:
           case LTC_ASN1_SETOF:
           case LTC_ASN1_SEQUENCE:
               if (der_decode_sequence(in, *inlen, data, size) == CRYPT_OK) {
                  if (der_length_sequence(data, size, &z) == CRYPT_OK) {
                     list[x].used = 1;
                     *inlen       = z;
                     return CRYPT_OK;
                  }
               }
               break;

           case LTC_ASN1_CHOICE:
           case LTC_ASN1_CONSTRUCTED:
           case LTC_ASN1_CONTEXT_SPECIFIC:
           case LTC_ASN1_EOL:
               return CRYPT_INVALID_ARG;
       }
   }

   return CRYPT_INVALID_PACKET;
}

#endif

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