ecdh-eddsa implementation now works

1 files changed, 189 insertions, 4 deletions

diff --git a/src/util/crypto_ecc.c b/src/util/crypto_ecc.c
index c3a60e841..a29e27a44 100644
--- a/src/util/crypto_ecc.c
+++ b/src/util/crypto_ecc.c
@@ -1430,7 +1430,9 @@ derive_h (const struct GNUNET_CRYPTO_EcdsaPublicKey *pub,
                      label, strlen (label),
                      context, strlen (context),
                      NULL, 0);
-  GNUNET_CRYPTO_mpi_scan_unsigned (&h, (unsigned char *) &hc, sizeof (hc));
+  GNUNET_CRYPTO_mpi_scan_unsigned (&h,
+                                   (unsigned char *) &hc,
+                                   sizeof (hc));
   return h;
 }
 
@@ -1466,7 +1468,9 @@ GNUNET_CRYPTO_ecdsa_private_key_derive (const struct GNUNET_CRYPTO_EcdsaPrivateK
   GNUNET_CRYPTO_ecdsa_key_get_public (priv, &pub);
 
   h = derive_h (&pub, label, context);
-  GNUNET_CRYPTO_mpi_scan_unsigned (&x, priv->d, sizeof (priv->d));
+  GNUNET_CRYPTO_mpi_scan_unsigned (&x,
+                                   priv->d,
+                                   sizeof (priv->d));
   d = gcry_mpi_new (256);
   gcry_mpi_mulm (d, h, x, n);
   gcry_mpi_release (h);
@@ -1543,6 +1547,78 @@ GNUNET_CRYPTO_ecdsa_public_key_derive (const struct GNUNET_CRYPTO_EcdsaPublicKey
 
 
 /**
+ * Reverse the sequence of the bytes in @a buffer
+ *
+ * @param[in|out] buffer buffer to invert
+ * @param length number of bytes in @a buffer
+ */
+static void
+reverse_buffer (unsigned char *buffer,
+                size_t length)
+{
+  unsigned char tmp;
+  size_t i;
+
+  for (i=0; i < length/2; i++)
+  {
+    tmp = buffer[i];
+    buffer[i] = buffer[length-1-i];
+    buffer[length-1-i] = tmp;
+  }
+}
+
+
+/**
+ * Convert the secret @a d of an EdDSA key to the
+ * value that is actually used in the EdDSA computation.
+ *
+ * @param d secret input
+ * @return value used for the calculation in EdDSA
+ */
+static gcry_mpi_t
+eddsa_d_to_a (gcry_mpi_t d)
+{
+  unsigned char rawmpi[32]; /* 256-bit value */
+  size_t rawmpilen;
+  unsigned char digest[64]; /* 512-bit hash value */
+  gcry_buffer_t hvec[2];
+  int b;
+  gcry_mpi_t a;
+
+  b = 256 / 8; /* number of bytes in `d` */
+  
+  /* Note that we clear DIGEST so we can use it as input to left pad
+     the key with zeroes for hashing.  */
+  memset (hvec, 0, sizeof hvec);
+  rawmpilen = sizeof (rawmpi);
+  GNUNET_assert (0 ==
+                 gcry_mpi_print (GCRYMPI_FMT_USG,
+                                 rawmpi, rawmpilen, &rawmpilen,
+                                 d));
+  hvec[0].data = digest;
+  hvec[0].off = 0;
+  hvec[0].len = b > rawmpilen? b - rawmpilen : 0;
+  hvec[1].data = rawmpi;
+  hvec[1].off = 0;
+  hvec[1].len = rawmpilen;
+  GNUNET_assert (0 ==
+                 gcry_md_hash_buffers (GCRY_MD_SHA512,
+                                       0 /* flags */,
+                                       digest,
+                                       hvec, 2));
+  /* Compute the A value.  */
+  reverse_buffer (digest, 32);  /* Only the first half of the hash.  */
+  digest[0]   = (digest[0] & 0x7f) | 0x40;
+  digest[31] &= 0xf8;
+
+  GNUNET_CRYPTO_mpi_scan_unsigned (&a,
+                                   digest,
+                                   32);
+  return a;
+}
+
+
+/**
  * @ingroup crypto
  * Derive key material from a ECDH public key and a private EdDSA key.
  * Dual to #GNUNET_CRRYPTO_ecdh_eddsa.
@@ -1557,7 +1633,64 @@ GNUNET_CRYPTO_eddsa_ecdh (const struct GNUNET_CRYPTO_EddsaPrivateKey *priv,
                           const struct GNUNET_CRYPTO_EcdhePublicKey *pub,
                           struct GNUNET_HashCode *key_material)
 {
-  return GNUNET_SYSERR;
+  gcry_mpi_point_t result;
+  gcry_mpi_point_t q;
+  gcry_mpi_t d;
+  gcry_mpi_t a;
+  gcry_ctx_t ctx;
+  gcry_sexp_t pub_sexpr;
+  gcry_mpi_t result_x;
+  unsigned char xbuf[256 / 8];
+  size_t rsize;
+
+  /* first, extract the q = dP value from the public key */
+  if (0 != gcry_sexp_build (&pub_sexpr, NULL,
+                            "(public-key(ecc(curve " CURVE ")(q %b)))",
+                            (int)sizeof (pub->q_y), pub->q_y))
+    return GNUNET_SYSERR;
+  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, pub_sexpr, NULL));
+  gcry_sexp_release (pub_sexpr);
+  q = gcry_mpi_ec_get_point ("q", ctx, 0);
+
+  /* second, extract the d value from our private key */
+  GNUNET_CRYPTO_mpi_scan_unsigned (&d, priv->d, sizeof (priv->d));
+
+  /* NOW, because this is EdDSA, HASH 'd' first! */
+  a = eddsa_d_to_a (d);
+  gcry_mpi_release (d);
+    
+  /* then call the 'multiply' function, to compute the product */
+  result = gcry_mpi_point_new (0);
+  gcry_mpi_ec_mul (result, a, q, ctx);
+  gcry_mpi_point_release (q);
+  gcry_mpi_release (a);
+
+  /* finally, convert point to string for hashing */
+  result_x = gcry_mpi_new (256);
+  if (gcry_mpi_ec_get_affine (result_x, NULL, result, ctx))
+  {
+    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "get_affine failed", 0);
+    gcry_mpi_point_release (result);
+    gcry_ctx_release (ctx);
+    return GNUNET_SYSERR;
+  }
+  gcry_mpi_point_release (result);
+  gcry_ctx_release (ctx);
+
+  rsize = sizeof (xbuf);
+  GNUNET_assert (! gcry_mpi_get_flag (result_x, GCRYMPI_FLAG_OPAQUE));
+  /* result_x can be negative here, so we do not use 'GNUNET_CRYPTO_mpi_print_unsigned'
+     as that does not include the sign bit; x should be a 255-bit
+     value, so with the sign it should fit snugly into the 256-bit
+     xbuf */
+  GNUNET_assert (0 ==
+                 gcry_mpi_print (GCRYMPI_FMT_STD, xbuf, rsize, &rsize,
+                                 result_x));
+  GNUNET_CRYPTO_hash (xbuf,
+                      rsize,
+                      key_material);
+  gcry_mpi_release (result_x);
+  return GNUNET_OK;
 }
 
 
@@ -1576,7 +1709,59 @@ GNUNET_CRYPTO_ecdh_eddsa (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv,
                           const struct GNUNET_CRYPTO_EddsaPublicKey *pub,
                           struct GNUNET_HashCode *key_material)
 {
-  return GNUNET_SYSERR;
+  gcry_mpi_point_t result;
+  gcry_mpi_point_t q;
+  gcry_mpi_t d;
+  gcry_ctx_t ctx;
+  gcry_sexp_t pub_sexpr;
+  gcry_mpi_t result_x;
+  unsigned char xbuf[256 / 8];
+  size_t rsize;
+
+  /* first, extract the q = dP value from the public key */
+  if (0 != gcry_sexp_build (&pub_sexpr, NULL,
+                            "(public-key(ecc(curve " CURVE ")(q %b)))",
+                            (int)sizeof (pub->q_y), pub->q_y))
+    return GNUNET_SYSERR;
+  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, pub_sexpr, NULL));
+  gcry_sexp_release (pub_sexpr);
+  q = gcry_mpi_ec_get_point ("q", ctx, 0);
+
+  /* second, extract the d value from our private key */
+  GNUNET_CRYPTO_mpi_scan_unsigned (&d, priv->d, sizeof (priv->d));
+
+  /* then call the 'multiply' function, to compute the product */
+  result = gcry_mpi_point_new (0);
+  gcry_mpi_ec_mul (result, d, q, ctx);
+  gcry_mpi_point_release (q);
+  gcry_mpi_release (d);
+
+  /* finally, convert point to string for hashing */
+  result_x = gcry_mpi_new (256);
+  if (gcry_mpi_ec_get_affine (result_x, NULL, result, ctx))
+  {
+    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "get_affine failed", 0);
+    gcry_mpi_point_release (result);
+    gcry_ctx_release (ctx);
+    return GNUNET_SYSERR;
+  }
+  gcry_mpi_point_release (result);
+  gcry_ctx_release (ctx);
+
+  rsize = sizeof (xbuf);
+  GNUNET_assert (! gcry_mpi_get_flag (result_x, GCRYMPI_FLAG_OPAQUE));
+  /* result_x can be negative here, so we do not use 'GNUNET_CRYPTO_mpi_print_unsigned'
+     as that does not include the sign bit; x should be a 255-bit
+     value, so with the sign it should fit snugly into the 256-bit
+     xbuf */
+  GNUNET_assert (0 ==
+                 gcry_mpi_print (GCRYMPI_FMT_STD, xbuf, rsize, &rsize,
+                                 result_x));
+  GNUNET_CRYPTO_hash (xbuf,
+                      rsize,
+                      key_material);
+  gcry_mpi_release (result_x);
+  return GNUNET_OK;
 }