-fix the fix

[oweals/gnunet.git] / src / util / crypto_kdf.c

diff --git a/src/util/crypto_kdf.c b/src/util/crypto_kdf.c
index d8fcbd8665d739be44bd719e6a6bf93339ba4ec5..b62b5c8478fd1168c4a747d26785c6b0d6855bab 100644 (file)
--- a/src/util/crypto_kdf.c
+++ b/src/util/crypto_kdf.c
@@ -1,10 +1,10 @@
 /*
      This file is part of GNUnet.
-     (C) 2010 Christian Grothoff (and other contributing authors)
+     Copyright (C) 2010 GNUnet e.V.
 
      GNUnet 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; either version 2, or (at your
+     by the Free Software Foundation; either version 3, or (at your
      option) any later version.
 
      GNUnet is distributed in the hope that it will be useful, but
@@ -14,14 +14,15 @@
 
      You should have received a copy of the GNU General Public License
      along with GNUnet; see the file COPYING.  If not, write to the
-     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-     Boston, MA 02111-1307, USA.
+     Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+     Boston, MA 02110-1301, USA.
 */
 
 /**
  * @file src/util/crypto_kdf.c
  * @brief Key derivation
  * @author Nils Durner
+ * @author Jeffrey Burdges <burdges@gnunet.org>
  */
 
 #include <gcrypt.h>
@@ -36,16 +37,17 @@
  * @param result buffer for the derived key, allocated by caller
  * @param out_len desired length of the derived key
  * @param xts salt
- * @param xts_len length of xts
+ * @param xts_len length of @a xts
  * @param skm source key material
- * @param skm_len length of skm
+ * @param skm_len length of @a skm
  * @param argp va_list of void * & size_t pairs for context chunks
- * @return GNUNET_YES on success
+ * @return #GNUNET_YES on success
  */
 int
-GNUNET_CRYPTO_kdf_v (void *result, size_t out_len, const void *xts,
-                    size_t xts_len, const void *skm, size_t skm_len,
-                    va_list argp)
+GNUNET_CRYPTO_kdf_v (void *result, size_t out_len,
+                     const void *xts, size_t xts_len,
+                     const void *skm, size_t skm_len,
+                     va_list argp)
 {
   /*
    * "Finally, we point out to a particularly advantageous instantiation using
@@ -59,33 +61,93 @@ GNUNET_CRYPTO_kdf_v (void *result, size_t out_len, const void *xts,
    * http://eprint.iacr.org/2010/264
    */
 
-  return GNUNET_CRYPTO_hkdf_v (result, out_len, GCRY_MD_SHA512,
-                              GCRY_MD_SHA256, xts, xts_len, skm, skm_len,
-                              argp);
+  return GNUNET_CRYPTO_hkdf_v (result, out_len, GCRY_MD_SHA512, GCRY_MD_SHA256,
+                               xts, xts_len, skm, skm_len, argp);
 }
 
+
 /**
  * @brief Derive key
  * @param result buffer for the derived key, allocated by caller
  * @param out_len desired length of the derived key
  * @param xts salt
- * @param xts_len length of xts
+ * @param xts_len length of @a xts
  * @param skm source key material
- * @param skm_len length of skm
+ * @param skm_len length of @a skm
  * @param ... void * & size_t pairs for context chunks
- * @return GNUNET_YES on success
+ * @return #GNUNET_YES on success
  */
 int
-GNUNET_CRYPTO_kdf (void *result, size_t out_len, const void *xts,
-                  size_t xts_len, const void *skm, size_t skm_len, ...)
+GNUNET_CRYPTO_kdf (void *result, size_t out_len,
+                   const void *xts, size_t xts_len,
+                   const void *skm, size_t skm_len, ...)
 {
   va_list argp;
   int ret;
 
   va_start (argp, skm_len);
-  ret =
-    GNUNET_CRYPTO_kdf_v (result, out_len, xts, xts_len, skm, skm_len, argp);
+  ret = GNUNET_CRYPTO_kdf_v (result, out_len, xts, xts_len, skm, skm_len, argp);
   va_end (argp);
 
   return ret;
 }
+
+
+/**
+ * Deterministically generate a pseudo-random number uniformly from the
+ * integers modulo a libgcrypt mpi.
+ *
+ * @param[out] r MPI value set to the FDH
+ * @param n MPI to work modulo
+ * @param xts salt
+ * @param xts_len length of @a xts
+ * @param skm source key material
+ * @param skm_len length of @a skm
+ * @param ctx context string
+ */
+void
+GNUNET_CRYPTO_kdf_mod_mpi (gcry_mpi_t *r,
+                           gcry_mpi_t n,
+                           const void *xts,  size_t xts_len,
+                           const void *skm,  size_t skm_len,
+                           const char *ctx)
+{
+  gcry_error_t rc;
+  unsigned int nbits;
+  size_t rsize;
+  unsigned int ctr;
+
+  nbits = gcry_mpi_get_nbits (n);
+  /* GNUNET_assert (nbits > 512); */
+
+  ctr = 0;
+  while (1)
+  {
+    /* Ain't clear if n is always divisible by 8 */
+    uint8_t buf[ (nbits-1)/8 + 1 ];
+
+    rc = GNUNET_CRYPTO_kdf (buf,
+                            sizeof (buf),
+                            xts, xts_len,
+                            skm, skm_len,
+                            ctx, strlen(ctx),
+                            &ctr, sizeof(ctr),
+                            NULL, 0);
+    GNUNET_assert (GNUNET_YES == rc);
+
+    rc = gcry_mpi_scan (r,
+                        GCRYMPI_FMT_USG,
+                        (const unsigned char *) buf,
+                        sizeof (buf),
+                        &rsize);
+    GNUNET_assert (0 == rc);  /* Allocation erro? */
+
+    gcry_mpi_clear_highbit (*r, nbits);
+    GNUNET_assert( 0 == gcry_mpi_test_bit (*r, nbits) );
+    ++ctr;
+    /* We reject this FDH if either *r > n and retry with another ctr */
+    if (0 > gcry_mpi_cmp(*r, n))
+      break;
+    gcry_mpi_release (*r);
+  }
+}