src/hash_questions.c

/* Copyright (c) 2012-2020 Simon Kelley

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 dated June, 1991, or
   (at your option) version 3 dated 29 June, 2007.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/


/* Hash the question section. This is used to safely detect query 
   retransmission and to detect answers to questions we didn't ask, which 
   might be poisoning attacks. Note that we decode the name rather 
   than CRC the raw bytes, since replies might be compressed differently. 
   We ignore case in the names for the same reason. 

   The hash used is SHA-256. If we're building with DNSSEC support,
   we use the Nettle cypto library. If not, we prefer not to
   add a dependency on Nettle, and use a stand-alone implementaion. 
*/

#include "dnsmasq.h"

#if defined(HAVE_DNSSEC) || defined(HAVE_CRYPTOHASH)

static const struct nettle_hash *hash;
static void *ctx;
static unsigned char *digest;

void hash_questions_init(void)
{
  if (!(hash = hash_find("sha256")))
    die(_("Failed to create SHA-256 hash object"), NULL, EC_MISC);

  ctx = safe_malloc(hash->context_size);
  digest = safe_malloc(hash->digest_size);
}

unsigned char *hash_questions(struct dns_header *header, size_t plen, char *name)
{
  int q;
  unsigned char *p = (unsigned char *)(header+1);

  hash->init(ctx);

  for (q = ntohs(header->qdcount); q != 0; q--) 
    {
      char *cp, c;

      if (!extract_name(header, plen, &p, name, 1, 4))
	break; /* bad packet */

      for (cp = name; (c = *cp); cp++)
	 if (c >= 'A' && c <= 'Z')
	   *cp += 'a' - 'A';

      hash->update(ctx, cp - name, (unsigned char *)name);
      /* CRC the class and type as well */
      hash->update(ctx, 4, p);

      p += 4;
      if (!CHECK_LEN(header, p, plen, 0))
	break; /* bad packet */
    }
  
  hash->digest(ctx, hash->digest_size, digest);
  return digest;
}

#else /* HAVE_DNSSEC  || HAVE_CRYPTOHASH */

#define SHA256_BLOCK_SIZE 32            // SHA256 outputs a 32 byte digest
typedef unsigned char BYTE;             // 8-bit byte
typedef unsigned int  WORD;             // 32-bit word, change to "long" for 16-bit machines

typedef struct {
  BYTE data[64];
  WORD datalen;
  unsigned long long bitlen;
  WORD state[8];
} SHA256_CTX;

static void sha256_init(SHA256_CTX *ctx);
static void sha256_update(SHA256_CTX *ctx, const BYTE data[], size_t len);
static void sha256_final(SHA256_CTX *ctx, BYTE hash[]);

void hash_questions_init(void)
{
}

unsigned char *hash_questions(struct dns_header *header, size_t plen, char *name)
{
  int q;
  unsigned char *p = (unsigned char *)(header+1);
  SHA256_CTX ctx;
  static BYTE digest[SHA256_BLOCK_SIZE];
  
  sha256_init(&ctx);
    
  for (q = ntohs(header->qdcount); q != 0; q--) 
    {
      char *cp, c;

      if (!extract_name(header, plen, &p, name, 1, 4))
	break; /* bad packet */

      for (cp = name; (c = *cp); cp++)
	 if (c >= 'A' && c <= 'Z')
	   *cp += 'a' - 'A';

      sha256_update(&ctx, (BYTE *)name, cp - name);
      /* CRC the class and type as well */
      sha256_update(&ctx, (BYTE *)p, 4);

      p += 4;
      if (!CHECK_LEN(header, p, plen, 0))
	break; /* bad packet */
    }
  
  sha256_final(&ctx, digest);
  return (unsigned char *)digest;
}

/* Code from here onwards comes from https://github.com/B-Con/crypto-algorithms
   and was written by Brad Conte (brad@bradconte.com), to whom all credit is given.

   This code is in the public domain, and the copyright notice at the head of this 
   file does not apply to it.
*/


/****************************** MACROS ******************************/
#define ROTLEFT(a,b) (((a) << (b)) | ((a) >> (32-(b))))
#define ROTRIGHT(a,b) (((a) >> (b)) | ((a) << (32-(b))))

#define CH(x,y,z) (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x,y,z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x) (ROTRIGHT(x,2) ^ ROTRIGHT(x,13) ^ ROTRIGHT(x,22))
#define EP1(x) (ROTRIGHT(x,6) ^ ROTRIGHT(x,11) ^ ROTRIGHT(x,25))
#define SIG0(x) (ROTRIGHT(x,7) ^ ROTRIGHT(x,18) ^ ((x) >> 3))
#define SIG1(x) (ROTRIGHT(x,17) ^ ROTRIGHT(x,19) ^ ((x) >> 10))

/**************************** VARIABLES *****************************/
static const WORD k[64] = {
			   0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
			   0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
			   0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
			   0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
			   0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
			   0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
			   0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
			   0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
};

/*********************** FUNCTION DEFINITIONS ***********************/
static void sha256_transform(SHA256_CTX *ctx, const BYTE data[])
{
  WORD a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];
  
  for (i = 0, j = 0; i < 16; ++i, j += 4)
    m[i] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) | (data[j + 3]);
  for ( ; i < 64; ++i)
    m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];

  a = ctx->state[0];
  b = ctx->state[1];
  c = ctx->state[2];
  d = ctx->state[3];
  e = ctx->state[4];
  f = ctx->state[5];
  g = ctx->state[6];
  h = ctx->state[7];

  for (i = 0; i < 64; ++i)
    {
      t1 = h + EP1(e) + CH(e,f,g) + k[i] + m[i];
      t2 = EP0(a) + MAJ(a,b,c);
      h = g;
      g = f;
      f = e;
      e = d + t1;
      d = c;
      c = b;
      b = a;
      a = t1 + t2;
    }
  
  ctx->state[0] += a;
  ctx->state[1] += b;
  ctx->state[2] += c;
  ctx->state[3] += d;
  ctx->state[4] += e;
  ctx->state[5] += f;
  ctx->state[6] += g;
  ctx->state[7] += h;
}

static void sha256_init(SHA256_CTX *ctx)
{
  ctx->datalen = 0;
  ctx->bitlen = 0;
  ctx->state[0] = 0x6a09e667;
  ctx->state[1] = 0xbb67ae85;
  ctx->state[2] = 0x3c6ef372;
  ctx->state[3] = 0xa54ff53a;
  ctx->state[4] = 0x510e527f;
  ctx->state[5] = 0x9b05688c;
  ctx->state[6] = 0x1f83d9ab;
  ctx->state[7] = 0x5be0cd19;
}

static void sha256_update(SHA256_CTX *ctx, const BYTE data[], size_t len)
{
  WORD i;
  
  for (i = 0; i < len; ++i)
    {
      ctx->data[ctx->datalen] = data[i];
      ctx->datalen++;
      if (ctx->datalen == 64) {
	sha256_transform(ctx, ctx->data);
	ctx->bitlen += 512;
	ctx->datalen = 0;
      }
    }
}

static void sha256_final(SHA256_CTX *ctx, BYTE hash[])
{
  WORD i;
  
  i = ctx->datalen;

  // Pad whatever data is left in the buffer.
  if (ctx->datalen < 56)
    {
      ctx->data[i++] = 0x80;
      while (i < 56)
	ctx->data[i++] = 0x00;
    }
  else
    {
      ctx->data[i++] = 0x80;
      while (i < 64)
	ctx->data[i++] = 0x00;
      sha256_transform(ctx, ctx->data);
      memset(ctx->data, 0, 56);
    }
  
  // Append to the padding the total message's length in bits and transform.
  ctx->bitlen += ctx->datalen * 8;
  ctx->data[63] = ctx->bitlen;
  ctx->data[62] = ctx->bitlen >> 8;
  ctx->data[61] = ctx->bitlen >> 16;
  ctx->data[60] = ctx->bitlen >> 24;
  ctx->data[59] = ctx->bitlen >> 32;
  ctx->data[58] = ctx->bitlen >> 40;
  ctx->data[57] = ctx->bitlen >> 48;
  ctx->data[56] = ctx->bitlen >> 56;
  sha256_transform(ctx, ctx->data);
  
  // Since this implementation uses little endian byte ordering and SHA uses big endian,
  // reverse all the bytes when copying the final state to the output hash.
  for (i = 0; i < 4; ++i)
    {
      hash[i]      = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
      hash[i + 4]  = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
      hash[i + 8]  = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
      hash[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0x000000ff;
      hash[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0x000000ff;
      hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
      hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
      hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
    }
}

#endif