view libtomcrypt/src/pk/asn1/der/ia5/der_encode_ia5_string.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
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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_encode_ia5_string.c
  ASN.1 DER, encode a IA5 STRING, Tom St Denis
*/

#ifdef LTC_DER

/**
  Store an IA5 STRING
  @param in       The array of IA5 to store (one per char)
  @param inlen    The number of IA5 to store
  @param out      [out] The destination for the DER encoded IA5 STRING
  @param outlen   [in/out] The max size and resulting size of the DER IA5 STRING
  @return CRYPT_OK if successful
*/
int der_encode_ia5_string(const unsigned char *in, unsigned long inlen,
                                unsigned char *out, unsigned long *outlen)
{
   unsigned long x, y, len;
   int           err;

   LTC_ARGCHK(in     != NULL);
   LTC_ARGCHK(out    != NULL);
   LTC_ARGCHK(outlen != NULL);

   /* get the size */
   if ((err = der_length_ia5_string(in, inlen, &len)) != CRYPT_OK) {
      return err;
   }

   /* too big? */
   if (len > *outlen) {
      *outlen = len;
      return CRYPT_BUFFER_OVERFLOW;
   }

   /* encode the header+len */
   x = 0;
   out[x++] = 0x16;
   if (inlen < 128) {
      out[x++] = (unsigned char)inlen;
   } else if (inlen < 256) {
      out[x++] = 0x81;
      out[x++] = (unsigned char)inlen;
   } else if (inlen < 65536UL) {
      out[x++] = 0x82;
      out[x++] = (unsigned char)((inlen>>8)&255);
      out[x++] = (unsigned char)(inlen&255);
   } else if (inlen < 16777216UL) {
      out[x++] = 0x83;
      out[x++] = (unsigned char)((inlen>>16)&255);
      out[x++] = (unsigned char)((inlen>>8)&255);
      out[x++] = (unsigned char)(inlen&255);
   } else {
      return CRYPT_INVALID_ARG;
   }

   /* store octets */
   for (y = 0; y < inlen; y++) {
       out[x++] = der_ia5_char_encode(in[y]);
   }

   /* retun length */
   *outlen = x;

   return CRYPT_OK;
}

#endif

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