Add ECDH primitives

include/polarssl/ecdh.h

@@ -33,9 +33,35 @@
 extern "C" {
 #endif
 
-#ifdef __cplusplus
-}
-#endif
+/**
+ * \brief           Generate a public key
+ *
+ * \param grp       ECP group
+ * \param d         Destination MPI (secret exponent)
+ * \param Q         Destination point (public key)
+ * \param f_rng     RNG function
+ * \param p_rng     RNG parameter
+ *
+ * \return          0 if successful,
+ *                  or a POLARSSL_ERR_ECP_XXX or POLARSSL_MPI_XXX error code
+ */
+int ecdh_gen_public( const ecp_group *grp, mpi *d, ecp_point *Q,
+                     int (*f_rng)(void *, unsigned char *, size_t),
+                     void *p_rng );
+
+/**
+ * \brief           Compute shared secret
+ *
+ * \param grp       ECP group
+ * \param z         Destination MPI (shared secret)
+ * \param Q         Public key from other party
+ * \param d         Our secret exponent
+ *
+ * \return          0 if successful,
+ *                  or a POLARSSL_ERR_ECP_XXX or POLARSSL_MPI_XXX error code
+ */
+int ecdh_compute_shared( const ecp_group *grp, mpi *z,
+                         const ecp_point *Q, const mpi *d );
 
 /**
  * \brief          Checkup routine
@@ -44,4 +70,8 @@ extern "C" {
  */
 int ecdh_self_test( int verbose );
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif

include/polarssl/ecp.h

@@ -147,11 +147,22 @@ void ecp_group_free( ecp_group *grp );
 /**
  * \brief           Set a point to zero
  *
+ * \param pt        Destination point
+ *
  * \return          0 if successful,
  *                  POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
  */
 int ecp_set_zero( ecp_point *pt );
 
+/**
+ * \brief           Tell if a point is zero
+ *
+ * \param pt        Point to test
+ *
+ * \return          1 if point is zero, 0 otherwise
+ */
+int ecp_is_zero( ecp_point *pt );
+
 /**
  * \brief           Copy the contents of point Q into P
  *

library/ecdh.c

@@ -35,6 +35,45 @@
 
 #include "polarssl/ecdh.h"
 
+/*
+ * Generate public key: simple wrapper around ecp_gen_keypair
+ */
+int ecdh_gen_public( const ecp_group *grp, mpi *d, ecp_point *Q,
+                     int (*f_rng)(void *, unsigned char *, size_t),
+                     void *p_rng )
+{
+    return ecp_gen_keypair( grp, d, Q, f_rng, p_rng );
+}
+
+/*
+ * Compute shared secret (SEC1 3.3.1)
+ */
+int ecdh_compute_shared( const ecp_group *grp, mpi *z,
+                         const ecp_point *Q, const mpi *d )
+{
+    int ret;
+    ecp_point P;
+
+    ecp_point_init( &P );
+
+    /*
+     * Make sure Q is a valid pubkey before using it
+     */
+    MPI_CHK( ecp_check_pubkey( grp, Q ) );
+
+    MPI_CHK( ecp_mul( grp, &P, d, Q ) );
+
+    if( ecp_is_zero( &P ) )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    MPI_CHK( mpi_copy( z, &P.X ) );
+
+cleanup:
+    ecp_point_free( &P );
+
+    return( ret );
+}
+
 
 #if defined(POLARSSL_SELF_TEST)
 

library/ecp.c

@@ -121,6 +121,14 @@ cleanup:
     return( ret );
 }
 
+/*
+ * Tell if a point is zero
+ */
+int ecp_is_zero( ecp_point *pt )
+{
+    return( mpi_cmp_int( &pt->Z, 0 ) == 0 );
+}
+
 /*
  * Copy the contents of Q into P
  */