Simplify creation of secret from DH negotiation.

PKCS#11 says to use the low order bytes, and that's what we do
here. This bears more research to make sure we're doing this
in a standard way.

1 files changed, 59 insertions, 91 deletions

diff --git a/egg/egg-dh.c b/egg/egg-dh.c
index d90abc0..f162f4d 100644
--- a/egg/egg-dh.c
+++ b/egg/egg-dh.c
@@ -21,9 +21,10 @@
 
 #include "config.h"
 
-#include "egg-asn1.h"
 #include "egg-dh.h"
-#include "egg-openssl.h"
+#include "egg-secure-memory.h"
+
+#define DEBUG_DH_SECRET 0
 
 typedef struct _DHGroup {
 	const gchar *name;
@@ -238,16 +239,18 @@ egg_dh_default_params (const gchar *name, gcry_mpi_t *prime, gcry_mpi_t *base)
 	gcry_error_t gcry;
 
 	g_return_val_if_fail (name, FALSE);
-	g_return_val_if_fail (prime, FALSE);
-	g_return_val_if_fail (base, FALSE);
 
 	for (group = dh_groups; group->name; ++group) {
 		if (g_str_equal (group->name, name)) {
-			gcry = gcry_mpi_scan (prime, GCRYMPI_FMT_USG, group->prime, group->n_prime, NULL);
-			g_return_val_if_fail (gcry == 0, FALSE);
-			g_return_val_if_fail (gcry_mpi_get_nbits (*prime) == group->bits, FALSE);
-			gcry = gcry_mpi_scan (base, GCRYMPI_FMT_USG, group->base, group->n_base, NULL);
-			g_return_val_if_fail (gcry == 0, FALSE);
+			if (prime) {
+				gcry = gcry_mpi_scan (prime, GCRYMPI_FMT_USG, group->prime, group->n_prime, NULL);
+				g_return_val_if_fail (gcry == 0, FALSE);
+				g_return_val_if_fail (gcry_mpi_get_nbits (*prime) == group->bits, FALSE);
+			}
+			if (base) {
+				gcry = gcry_mpi_scan (base, GCRYMPI_FMT_USG, group->base, group->n_base, NULL);
+				g_return_val_if_fail (gcry == 0, FALSE);
+			}
 			return TRUE;
 		}
 	}
@@ -300,91 +303,56 @@ egg_dh_gen_pair (gcry_mpi_t p, gcry_mpi_t g, guint bits,
 	return TRUE;
 }
 
-gboolean
-egg_dh_gen_secret (gcry_mpi_t Y, gcry_mpi_t x,
-                   gcry_mpi_t p, gcry_mpi_t *k)
-{
-	gint bits;
-
-	g_return_val_if_fail (Y, FALSE);
-	g_return_val_if_fail (x, FALSE);
-	g_return_val_if_fail (p, FALSE);
-	g_return_val_if_fail (k, FALSE);
-
-	bits = gcry_mpi_get_nbits (p);
-	g_return_val_if_fail (bits >= 0, FALSE);
-
-	*k = gcry_mpi_snew (bits);
-	g_return_val_if_fail (*k, FALSE);
-	gcry_mpi_powm (*k, Y, x, p);
-
-	return TRUE;
-}
-
-typedef struct _Parameters {
-	gcry_mpi_t p;
-	gcry_mpi_t g;
-} Parameters;
-
-#ifndef EGG_DH_NO_ASN1
-
-static gboolean
-parse_der_pkcs3 (const guchar *data, gsize n_data, Parameters *params)
+gpointer
+egg_dh_gen_secret (gcry_mpi_t peer, gcry_mpi_t priv,
+                   gcry_mpi_t prime, gsize bytes)
 {
-	ASN1_TYPE asn;
-	guchar *buf_p, *buf_g;
-	gsize n_buf_p, n_buf_g;
 	gcry_error_t gcry;
+	guchar *value;
+	gsize n_value;
+	gsize offset = 0;
+	gcry_mpi_t k;
+	gint bits;
 
-	asn = egg_asn1_decode ("PK.DHParameter", data, n_data);
-	if (!asn)
-		return FALSE;
-
-	buf_p = egg_asn1_read_value (asn, "prime", &n_buf_p, (EggAllocator)g_realloc);
-	buf_g = egg_asn1_read_value (asn, "base", &n_buf_g, (EggAllocator)g_realloc);
-	g_return_val_if_fail (buf_p && buf_g, FALSE);
-	gcry = gcry_mpi_scan (&params->p, GCRYMPI_FMT_STD, buf_p, n_buf_p, &n_buf_p);
-	g_return_val_if_fail (gcry == 0, FALSE);
-	gcry = gcry_mpi_scan (&params->g, GCRYMPI_FMT_STD, buf_g, n_buf_g, &n_buf_g);
-	g_return_val_if_fail (gcry == 0, FALSE);
-
-	g_free (buf_p);
-	g_free (buf_g);
-	return TRUE;
-}
-
-static void
-parse_openssl_pkcs3 (GQuark type, const guchar *data, gsize n_data,
-                     GHashTable *headers, gpointer user_data)
-{
-	Parameters *params = user_data;
-
-	/* Only parse the first one */
-	if (params->p != NULL)
-		return;
-
-	if (g_quark_try_string ("DH PARAMETERS") == type)
-		parse_der_pkcs3 (data, n_data, params);
-}
-
-gboolean
-egg_dh_parse_pkcs3 (const guchar *data, gsize n_data, gcry_mpi_t *p, gcry_mpi_t *g)
-{
-	Parameters params;
-
-	g_return_val_if_fail (data, FALSE);
-	g_return_val_if_fail (p, FALSE);
-	g_return_val_if_fail (g, FALSE);
+	g_return_val_if_fail (peer, NULL);
+	g_return_val_if_fail (priv, NULL);
+	g_return_val_if_fail (prime, NULL);
+
+	bits = gcry_mpi_get_nbits (prime);
+	g_return_val_if_fail (bits >= 0, NULL);
+
+	k = gcry_mpi_snew (bits);
+	g_return_val_if_fail (k, NULL);
+	gcry_mpi_powm (k, peer, priv, prime);
+
+	/* Write out the secret */
+	gcry = gcry_mpi_print (GCRYMPI_FMT_USG, NULL, 0, &n_value, k);
+	g_return_val_if_fail (gcry == 0, NULL);
+	if (n_value < bytes)
+		offset = bytes - n_value;
+	value = egg_secure_alloc (n_value + offset);
+	memset (value, 0, n_value + offset);
+	gcry = gcry_mpi_print (GCRYMPI_FMT_USG, value + offset, n_value, &n_value, k);
+	g_return_val_if_fail (gcry == 0, NULL);
+
+#if DEBUG_DH_SECRET
+	g_printerr ("DH SECRET: ");
+	gcry_mpi_dump (k);
+	gcry_mpi_release (k);
+#endif
+
+	if (bytes != 0 && bytes < n_value) {
+		offset = n_value - bytes;
+		memmove (value, value + offset, bytes);
+		egg_secure_clear (value + bytes, offset);
+	}
 
-	memset (&params, 0, sizeof (params));
-	if (!parse_der_pkcs3 (data, n_data, &params))
-		egg_openssl_pem_parse (data, n_data, parse_openssl_pkcs3, &params);
+#if DEBUG_DH_SECRET
+	gcry_mpi_scan (&k, GCRYMPI_FMT_USG, value, bytes, NULL);
+	g_printerr ("RAW SECRET: ");
+	gcry_mpi_dump (k);
+	gcry_mpi_release (k);
+#endif
 
-	if (!params.p || !params.g)
-		return FALSE;
-	*p = params.p;
-	*g = params.g;
-	return TRUE;
+	return value;
 }
-
-#endif /* EGG_DH_NO_ASN1 */