/*
    Copyright (c) 2010 Nils Durner

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
 */

/**
 * @file src/util/crypto_hkdf.c
 * @brief Hash-based KDF as defined in RFC 5869
 * @see http://www.rfc-editor.org/rfc/rfc5869.txt
 * @todo remove GNUNET references
 * @author Nils Durner
 *
 * The following list of people have reviewed this code and considered
 * it correct on the date given (if you reviewed it, please
 * have your name added to the list):
 *
 * - Christian Grothoff (08.10.2010)
 * - Nathan Evans (08.10.2010)
 * - Matthias Wachs (08.10.2010)
 */

#define LOG(kind, ...) GNUNET_log_from (kind, "util-crypto-hkdf", __VA_ARGS__)

/**
 * Set this to 0 if you compile this code outside of GNUnet.
 */
#define GNUNET_BUILD 1

/**
 * Enable debugging.
 */
#define DEBUG_HKDF 0


#if GNUNET_BUILD

#include "platform.h"
#include "gnunet_util_lib.h"
#include "benchmark.h"
#else
#define GNUNET_NO 0
#define GNUNET_YES 1
#define GNUNET_SYSERR -1
#include <stdlib.h>
#endif

#include <gcrypt.h>


/**
 * @brief Compute the HMAC
 * @todo use chunked buffers
 * @param mac gcrypt MAC handle
 * @param key HMAC key
 * @param key_len length of key
 * @param buf message to be processed
 * @param buf_len length of buf
 * @return HMAC, freed by caller via gcry_md_close/_reset
 */
static const void *
doHMAC (gcry_md_hd_t mac,
        const void *key,
        size_t key_len,
        const void *buf,
        size_t buf_len)
{
  if (GPG_ERR_NO_ERROR !=
      gcry_md_setkey (mac, key, key_len))
  {
    GNUNET_break (0);
    return NULL;
  }
  gcry_md_write (mac,
                 buf,
                 buf_len);
  return (const void *) gcry_md_read (mac, 0);
}


/**
 * @brief Generate pseudo-random key
 * @param mac gcrypt HMAC handle
 * @param xts salt
 * @param xts_len length of the @a xts salt
 * @param skm source key material
 * @param skm_len length of @a skm
 * @param prk result buffer (allocated by caller; at least gcry_md_dlen() bytes)
 * @return #GNUNET_YES on success
 */
static enum GNUNET_GenericReturnValue
getPRK (gcry_md_hd_t mac,
        const void *xts,
        size_t xts_len,
        const void *skm,
        size_t skm_len,
        void *prk)
{
  const void *ret;
  size_t dlen;

  dlen = gcry_md_get_algo_dlen (gcry_md_get_algo (mac));

  /* sanity check to bound stack allocation */
  GNUNET_assert (dlen <= 512);

  /* From RFC 5869:
   * salt - optional salt value (a non-secret random value);
   * if not provided, it is set to a string of HashLen zeros. */

  if (0 == xts_len)
  {
    char zero_salt[dlen];

    memset (zero_salt, 0, dlen);
    ret = doHMAC (mac, zero_salt, dlen, skm, skm_len);
  }
  else
  {
    ret = doHMAC (mac, xts, xts_len, skm, skm_len);
  }
  if (NULL == ret)
    return GNUNET_SYSERR;
  GNUNET_memcpy (prk,
                 ret,
                 dlen);
  return GNUNET_YES;
}


#if DEBUG_HKDF
static void
dump (const char *src,
      const void *p,
      unsigned int l)
{
  printf ("\n%s: ", src);
  for (unsigned int i = 0; i < l; i++)
  {
    printf ("%2x", (int) ((const unsigned char *) p)[i]);
  }
  printf ("\n");
}


#endif


enum GNUNET_GenericReturnValue
GNUNET_CRYPTO_hkdf_v (void *result,
                      size_t out_len,
                      int xtr_algo,
                      int prf_algo,
                      const void *xts,
                      size_t xts_len,
                      const void *skm,
                      size_t skm_len,
                      va_list argp)
{
  gcry_md_hd_t xtr;
  gcry_md_hd_t prf;
  const void *hc;
  unsigned long i;
  unsigned long t;
  unsigned long d;
  unsigned int k = gcry_md_get_algo_dlen (prf_algo);
  unsigned int xtr_len = gcry_md_get_algo_dlen (xtr_algo);
  char prk[xtr_len];
  int ret;
  size_t ctx_len;
  va_list args;

  BENCHMARK_START (hkdf);

  if (0 == k)
    return GNUNET_SYSERR;
  if (GPG_ERR_NO_ERROR !=
      gcry_md_open (&xtr,
                    xtr_algo,
                    GCRY_MD_FLAG_HMAC))
    return GNUNET_SYSERR;
  if (GPG_ERR_NO_ERROR !=
      gcry_md_open (&prf,
                    prf_algo,
                    GCRY_MD_FLAG_HMAC))
  {
    gcry_md_close (xtr);
    return GNUNET_SYSERR;
  }
  va_copy (args, argp);

  ctx_len = 0;
  while (NULL != va_arg (args, void *))
  {
    size_t nxt = va_arg (args, size_t);
    if (nxt + ctx_len < nxt)
    {
      /* integer overflow */
      GNUNET_break (0);
      va_end (args);
      goto hkdf_error;
    }
    ctx_len += nxt;
  }

  va_end (args);

  if ( (k + ctx_len < ctx_len) ||
       (k + ctx_len + 1 < ctx_len) )
  {
    /* integer overflow */
    GNUNET_break (0);
    goto hkdf_error;
  }

  memset (result, 0, out_len);
  if (GNUNET_YES !=
      getPRK (xtr, xts, xts_len, skm, skm_len, prk))
    goto hkdf_error;
#if DEBUG_HKDF
  dump ("PRK", prk, xtr_len);
#endif

  t = out_len / k;
  d = out_len % k;

  /* K(1) */
  {
    size_t plain_len = k + ctx_len + 1;
    char *plain;
    const void *ctx;
    char *dst;

    plain = GNUNET_malloc (plain_len);
    dst = plain + k;
    va_copy (args, argp);
    while ((ctx = va_arg (args, void *)))
    {
      size_t len;

      len = va_arg (args, size_t);
      GNUNET_memcpy (dst, ctx, len);
      dst += len;
    }
    va_end (args);

    if (t > 0)
    {
      plain[k + ctx_len] = (char) 1;
#if DEBUG_HKDF
      dump ("K(1)", plain, plain_len);
#endif
      hc = doHMAC (prf, prk, xtr_len, &plain[k], ctx_len + 1);
      if (hc == NULL)
      {
        GNUNET_free (plain);
        goto hkdf_error;
      }
      GNUNET_memcpy (result, hc, k);
      result += k;
    }

    /* K(i+1) */
    for (i = 1; i < t; i++)
    {
      GNUNET_memcpy (plain, result - k, k);
      plain[k + ctx_len] = (char) (i + 1);
      gcry_md_reset (prf);
#if DEBUG_HKDF
      dump ("K(i+1)", plain, plain_len);
#endif
      hc = doHMAC (prf, prk, xtr_len, plain, plain_len);
      if (NULL == hc)
      {
        GNUNET_free (plain);
        goto hkdf_error;
      }
      GNUNET_memcpy (result, hc, k);
      result += k;
    }

    /* K(t):d */
    if (d > 0)
    {
      if (t > 0)
      {
        GNUNET_memcpy (plain, result - k, k);
        i++;
      }
      plain[k + ctx_len] = (char) i;
      gcry_md_reset (prf);
#if DEBUG_HKDF
      dump ("K(t):d", plain, plain_len);
#endif
      if (t > 0)
        hc = doHMAC (prf, prk, xtr_len, plain, plain_len);
      else
        hc = doHMAC (prf, prk, xtr_len, plain + k, plain_len - k);
      if (hc == NULL)
      {
        GNUNET_free (plain);
        goto hkdf_error;
      }
      GNUNET_memcpy (result, hc, d);
    }
#if DEBUG_HKDF
    dump ("result", result - k, out_len);
#endif

    ret = GNUNET_YES;
    GNUNET_free (plain);
    goto hkdf_ok;
  }
hkdf_error:
  ret = GNUNET_SYSERR;
hkdf_ok:
  gcry_md_close (xtr);
  gcry_md_close (prf);
  BENCHMARK_END (hkdf);
  return ret;
}


enum GNUNET_GenericReturnValue
GNUNET_CRYPTO_hkdf (void *result,
                    size_t out_len,
                    int xtr_algo,
                    int prf_algo,
                    const void *xts,
                    size_t xts_len,
                    const void *skm,
                    size_t skm_len, ...)
{
  va_list argp;
  enum GNUNET_GenericReturnValue ret;

  va_start (argp, skm_len);
  ret =
    GNUNET_CRYPTO_hkdf_v (result,
                          out_len,
                          xtr_algo,
                          prf_algo,
                          xts,
                          xts_len,
                          skm,
                          skm_len,
                          argp);
  va_end (argp);
  return ret;
}


/* end of crypto_hkdf.c */
