Cache pre-computed points for ecp_mul()

Up to 1.25 speedup on ECDSA sign for small curves, but mainly useful as a
preparation for fixed-point mult (a few prototypes changed in constness).

include/polarssl/ecdh.h

@@ -62,7 +62,7 @@ ecdh_context;
  * \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 ecdh_gen_public( ecp_group *grp, mpi *d, ecp_point *Q,
                      int (*f_rng)(void *, unsigned char *, size_t),
                      void *p_rng );
 
@@ -83,7 +83,7 @@ int ecdh_gen_public( const ecp_group *grp, mpi *d, ecp_point *Q,
  *                  countermeasures against potential elaborate timing
  *                  attacks, see \c ecp_mul() for details.
  */
-int ecdh_compute_shared( const ecp_group *grp, mpi *z,
+int ecdh_compute_shared( ecp_group *grp, mpi *z,
                          const ecp_point *Q, const mpi *d,
                          int (*f_rng)(void *, unsigned char *, size_t),
                          void *p_rng );

include/polarssl/ecdsa.h

@@ -63,7 +63,7 @@ extern "C" {
  * \return          0 if successful,
  *                  or a POLARSSL_ERR_ECP_XXX or POLARSSL_MPI_XXX error code
  */
-int ecdsa_sign( const ecp_group *grp, mpi *r, mpi *s,
+int ecdsa_sign( ecp_group *grp, mpi *r, mpi *s,
                 const mpi *d, const unsigned char *buf, size_t blen,
                 int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
 
@@ -81,7 +81,7 @@ int ecdsa_sign( const ecp_group *grp, mpi *r, mpi *s,
  *                  POLARSSL_ERR_ECP_BAD_INPUT_DATA if signature is invalid
  *                  or a POLARSSL_ERR_ECP_XXX or POLARSSL_MPI_XXX error code
  */
-int ecdsa_verify( const ecp_group *grp,
+int ecdsa_verify( ecp_group *grp,
                   const unsigned char *buf, size_t blen,
                   const ecp_point *Q, const mpi *r, const mpi *s);
 

include/polarssl/ecp.h

@@ -155,16 +155,15 @@ ecp_keypair;
 
 /*
  * Maximum window size (actually, NAF width) used for point multipliation.
- * Default: 7.
+ * Default: 8.
  * Minimum value: 2. Maximum value: 8.
  *
  * Result is an array of at most ( 1 << ( POLARSSL_ECP_WINDOW_SIZE - 1 ) )
- * points used for point multiplication, so at most 64 by default.
- * In practice, most curves will use less precomputed points.
+ * points used for point multiplication.
  *
  * Reduction in size may reduce speed for big curves.
  */
-#define POLARSSL_ECP_WINDOW_SIZE    7   /**< Maximum NAF width used. */
+#define POLARSSL_ECP_WINDOW_SIZE    8   /**< Maximum NAF width used. */
 
 /*
  * Point formats, from RFC 4492's enum ECPointFormat
@@ -472,7 +471,7 @@ int ecp_sub( const ecp_group *grp, ecp_point *R,
  *                  has very low overhead, it is recommended to always provide
  *                  a non-NULL f_rng parameter when using secret inputs.
  */
-int ecp_mul( const ecp_group *grp, ecp_point *R,
+int ecp_mul( ecp_group *grp, ecp_point *R,
              const mpi *m, const ecp_point *P,
              int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
 
@@ -531,7 +530,7 @@ int ecp_check_privkey( const ecp_group *grp, const mpi *d );
  *                  in order to ease use with other structures such as
  *                  ecdh_context of ecdsa_context.
  */
-int ecp_gen_keypair( const ecp_group *grp, mpi *d, ecp_point *Q,
+int ecp_gen_keypair( ecp_group *grp, mpi *d, ecp_point *Q,
                      int (*f_rng)(void *, unsigned char *, size_t),
                      void *p_rng );