Check scalar->d before we use it (in BN_num_bits()). (Coverity ID 129)
[openssl.git] / crypto / ec / ec_mult.c
index 4978a54352ba5b8d828af9437a311cfda20a37b4..84488c9643ea9b3fc3bc0b55fb2ee9e15e0ec63c 100644 (file)
@@ -1,9 +1,9 @@
 /* crypto/ec/ec_mult.c */
 /*
- * Originally written by Bodo Moeller for the OpenSSL project.
+ * Originally written by Bodo Moeller and Nils Larsch for the OpenSSL project.
  */
 /* ====================================================================
- * Copyright (c) 1998-2002 The OpenSSL Project.  All rights reserved.
+ * Copyright (c) 1998-2007 The OpenSSL Project.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * and contributed to the OpenSSL project.
  */
 
+#include <string.h>
+
 #include <openssl/err.h>
 
 #include "ec_lcl.h"
 
 
-/* TODO: optional precomputation of multiples of the generator */
+/*
+ * This file implements the wNAF-based interleaving multi-exponentation method
+ * (<URL:http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#multiexp>);
+ * for multiplication with precomputation, we use wNAF splitting
+ * (<URL:http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#fastexp>).
+ */
 
 
 
-/*
- * wNAF-based interleaving multi-exponentation method
- * (<URL:http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#multiexp>)
- */
+
+/* structure for precomputed multiples of the generator */
+typedef struct ec_pre_comp_st {
+       const EC_GROUP *group; /* parent EC_GROUP object */
+       size_t blocksize;      /* block size for wNAF splitting */
+       size_t numblocks;      /* max. number of blocks for which we have precomputation */
+       size_t w;              /* window size */
+       EC_POINT **points;     /* array with pre-calculated multiples of generator:
+                               * 'num' pointers to EC_POINT objects followed by a NULL */
+       size_t num;            /* numblocks * 2^(w-1) */
+       int references;
+} EC_PRE_COMP;
+/* functions to manage EC_PRE_COMP within the EC_GROUP extra_data framework */
+static void *ec_pre_comp_dup(void *);
+static void ec_pre_comp_free(void *);
+static void ec_pre_comp_clear_free(void *);
+
+static EC_PRE_COMP *ec_pre_comp_new(const EC_GROUP *group)
+       {
+       EC_PRE_COMP *ret = NULL;
+
+       if (!group)
+               return NULL;
+
+       ret = (EC_PRE_COMP *)OPENSSL_malloc(sizeof(EC_PRE_COMP));
+       if (!ret)
+               {
+               ECerr(EC_F_EC_PRE_COMP_NEW, ERR_R_MALLOC_FAILURE);
+               return ret;
+               }
+       ret->group = group;
+       ret->blocksize = 8; /* default */
+       ret->numblocks = 0;
+       ret->w = 4; /* default */
+       ret->points = NULL;
+       ret->num = 0;
+       ret->references = 1;
+       return ret;
+       }
+
+static void *ec_pre_comp_dup(void *src_)
+       {
+       EC_PRE_COMP *src = src_;
+
+       /* no need to actually copy, these objects never change! */
+
+       CRYPTO_add(&src->references, 1, CRYPTO_LOCK_EC_PRE_COMP);
+
+       return src_;
+       }
+
+static void ec_pre_comp_free(void *pre_)
+       {
+       int i;
+       EC_PRE_COMP *pre = pre_;
+
+       if (!pre)
+               return;
+
+       i = CRYPTO_add(&pre->references, -1, CRYPTO_LOCK_EC_PRE_COMP);
+       if (i > 0)
+               return;
+
+       if (pre->points)
+               {
+               EC_POINT **p;
+
+               for (p = pre->points; *p != NULL; p++)
+                       EC_POINT_free(*p);
+               OPENSSL_free(pre->points);
+               }
+       OPENSSL_free(pre);
+       }
+
+static void ec_pre_comp_clear_free(void *pre_)
+       {
+       int i;
+       EC_PRE_COMP *pre = pre_;
+
+       if (!pre)
+               return;
+
+       i = CRYPTO_add(&pre->references, -1, CRYPTO_LOCK_EC_PRE_COMP);
+       if (i > 0)
+               return;
+
+       if (pre->points)
+               {
+               EC_POINT **p;
+
+               for (p = pre->points; *p != NULL; p++)
+                       EC_POINT_clear_free(*p);
+               OPENSSL_cleanse(pre->points, sizeof pre->points);
+               OPENSSL_free(pre->points);
+               }
+       OPENSSL_cleanse(pre, sizeof pre);
+       OPENSSL_free(pre);
+       }
+
+
 
 
 /* Determine the modified width-(w+1) Non-Adjacent Form (wNAF) of 'scalar'.
@@ -93,6 +197,19 @@ static signed char *compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len)
        int bit, next_bit, mask;
        size_t len = 0, j;
        
+       if (BN_is_zero(scalar))
+               {
+               r = OPENSSL_malloc(1);
+               if (!r)
+                       {
+                       ECerr(EC_F_COMPUTE_WNAF, ERR_R_MALLOC_FAILURE);
+                       goto err;
+                       }
+               r[0] = 0;
+               *ret_len = 1;
+               return r;
+               }
+               
        if (w <= 0 || w > 7) /* 'signed char' can represent integers with absolute values less than 2^7 */
                {
                ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
@@ -102,20 +219,26 @@ static signed char *compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len)
        next_bit = bit << 1; /* at most 256 */
        mask = next_bit - 1; /* at most 255 */
 
-       if (scalar->neg)
+       if (BN_is_negative(scalar))
                {
                sign = -1;
                }
 
-       len = BN_num_bits(scalar);
-       r = OPENSSL_malloc(len + 1); /* modified wNAF may be one digit longer than binary representation */
-       if (r == NULL) goto err;
-
        if (scalar->d == NULL || scalar->top == 0)
                {
                ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
                goto err;
                }
+
+       len = BN_num_bits(scalar);
+       r = OPENSSL_malloc(len + 1); /* modified wNAF may be one digit longer than binary representation
+                                     * (*ret_len will be set to the actual length, i.e. at most
+                                     * BN_num_bits(scalar) + 1) */
+       if (r == NULL)
+               {
+               ECerr(EC_F_COMPUTE_WNAF, ERR_R_MALLOC_FAILURE);
+               goto err;
+               }
        window_val = scalar->d[0] & mask;
        j = 0;
        while ((window_val != 0) || (j + w + 1 < len)) /* if j+w+1 >= len, window_val will not increase */
@@ -204,12 +327,13 @@ static signed char *compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len)
  *       (thus the boundaries should be increased)
  */
 #define EC_window_bits_for_scalar_size(b) \
-               ((b) >= 2000 ? 6 : \
-                (b) >=  800 ? 5 : \
-                (b) >=  300 ? 4 : \
-                (b) >=   70 ? 3 : \
-                (b) >=   20 ? 2 : \
-                 1)
+               ((size_t) \
+                ((b) >= 2000 ? 6 : \
+                 (b) >=  800 ? 5 : \
+                 (b) >=  300 ? 4 : \
+                 (b) >=   70 ? 3 : \
+                 (b) >=   20 ? 2 : \
+                 1))
 
 /* Compute
  *      \sum scalars[i]*points[i],
@@ -221,9 +345,11 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
        size_t num, const EC_POINT *points[], const BIGNUM *scalars[], BN_CTX *ctx)
        {
        BN_CTX *new_ctx = NULL;
-       EC_POINT *generator = NULL;
+       const EC_POINT *generator = NULL;
        EC_POINT *tmp = NULL;
        size_t totalnum;
+       size_t blocksize = 0, numblocks = 0; /* for wNAF splitting */
+       size_t pre_points_per_block = 0;
        size_t i, j;
        int k;
        int r_is_inverted = 0;
@@ -235,19 +361,23 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
        size_t num_val;
        EC_POINT **val = NULL; /* precomputation */
        EC_POINT **v;
-       EC_POINT ***val_sub = NULL; /* pointers to sub-arrays of 'val' */
+       EC_POINT ***val_sub = NULL; /* pointers to sub-arrays of 'val' or 'pre_comp->points' */
+       const EC_PRE_COMP *pre_comp = NULL;
+       int num_scalar = 0; /* flag: will be set to 1 if 'scalar' must be treated like other scalars,
+                            * i.e. precomputation is not available */
        int ret = 0;
        
-       if (scalar != NULL)
+       if (group->meth != r->meth)
                {
-               generator = EC_GROUP_get0_generator(group);
-               if (generator == NULL)
-                       {
-                       ECerr(EC_F_EC_WNAF_MUL, EC_R_UNDEFINED_GENERATOR);
-                       return 0;
-                       }
+               ECerr(EC_F_EC_WNAF_MUL, EC_R_INCOMPATIBLE_OBJECTS);
+               return 0;
                }
-       
+
+       if ((scalar == NULL) && (num == 0))
+               {
+               return EC_POINT_set_to_infinity(group, r);
+               }
+
        for (i = 0; i < num; i++)
                {
                if (group->meth != points[i]->meth)
@@ -257,40 +387,217 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
                        }
                }
 
-       totalnum = num + (scalar != NULL);
+       if (ctx == NULL)
+               {
+               ctx = new_ctx = BN_CTX_new();
+               if (ctx == NULL)
+                       goto err;
+               }
+
+       if (scalar != NULL)
+               {
+               generator = EC_GROUP_get0_generator(group);
+               if (generator == NULL)
+                       {
+                       ECerr(EC_F_EC_WNAF_MUL, EC_R_UNDEFINED_GENERATOR);
+                       goto err;
+                       }
+               
+               /* look if we can use precomputed multiples of generator */
+
+               pre_comp = EC_EX_DATA_get_data(group->extra_data, ec_pre_comp_dup, ec_pre_comp_free, ec_pre_comp_clear_free);
+
+               if (pre_comp && pre_comp->numblocks && (EC_POINT_cmp(group, generator, pre_comp->points[0], ctx) == 0))
+                       {
+                       blocksize = pre_comp->blocksize;
+
+                       /* determine maximum number of blocks that wNAF splitting may yield
+                        * (NB: maximum wNAF length is bit length plus one) */
+                       numblocks = (BN_num_bits(scalar) / blocksize) + 1;
+
+                       /* we cannot use more blocks than we have precomputation for */
+                       if (numblocks > pre_comp->numblocks)
+                               numblocks = pre_comp->numblocks;
+
+                       pre_points_per_block = 1u << (pre_comp->w - 1);
+
+                       /* check that pre_comp looks sane */
+                       if (pre_comp->num != (pre_comp->numblocks * pre_points_per_block))
+                               {
+                               ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
+                               goto err;
+                               }
+                       }
+               else
+                       {
+                       /* can't use precomputation */
+                       pre_comp = NULL;
+                       numblocks = 1;
+                       num_scalar = 1; /* treat 'scalar' like 'num'-th element of 'scalars' */
+                       }
+               }
+       
+       totalnum = num + numblocks;
 
-       wsize = OPENSSL_malloc(totalnum * sizeof wsize[0]);
+       wsize    = OPENSSL_malloc(totalnum * sizeof wsize[0]);
        wNAF_len = OPENSSL_malloc(totalnum * sizeof wNAF_len[0]);
-       wNAF = OPENSSL_malloc((totalnum + 1) * sizeof wNAF[0]);
-       if (wNAF != NULL)
+       wNAF     = OPENSSL_malloc((totalnum + 1) * sizeof wNAF[0]); /* includes space for pivot */
+       val_sub  = OPENSSL_malloc(totalnum * sizeof val_sub[0]);
+                
+       if (!wsize || !wNAF_len || !wNAF || !val_sub)
                {
-               wNAF[0] = NULL; /* preliminary pivot */
+               ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
+               goto err;
                }
-       if (wsize == NULL || wNAF_len == NULL || wNAF == NULL) goto err;
 
-       /* num_val := total number of points to precompute */
+       wNAF[0] = NULL; /* preliminary pivot */
+
+       /* num_val will be the total number of temporarily precomputed points */
        num_val = 0;
-       for (i = 0; i < totalnum; i++)
+
+       for (i = 0; i < num + num_scalar; i++)
                {
                size_t bits;
 
                bits = i < num ? BN_num_bits(scalars[i]) : BN_num_bits(scalar);
                wsize[i] = EC_window_bits_for_scalar_size(bits);
                num_val += 1u << (wsize[i] - 1);
+               wNAF[i + 1] = NULL; /* make sure we always have a pivot */
+               wNAF[i] = compute_wNAF((i < num ? scalars[i] : scalar), wsize[i], &wNAF_len[i]);
+               if (wNAF[i] == NULL)
+                       goto err;
+               if (wNAF_len[i] > max_len)
+                       max_len = wNAF_len[i];
+               }
+
+       if (numblocks)
+               {
+               /* we go here iff scalar != NULL */
+               
+               if (pre_comp == NULL)
+                       {
+                       if (num_scalar != 1)
+                               {
+                               ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
+                               goto err;
+                               }
+                       /* we have already generated a wNAF for 'scalar' */
+                       }
+               else
+                       {
+                       signed char *tmp_wNAF = NULL;
+                       size_t tmp_len = 0;
+                       
+                       if (num_scalar != 0)
+                               {
+                               ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
+                               goto err;
+                               }
+
+                       /* use the window size for which we have precomputation */
+                       wsize[num] = pre_comp->w;
+                       tmp_wNAF = compute_wNAF(scalar, wsize[num], &tmp_len);
+                       if (!tmp_wNAF)
+                               goto err;
+
+                       if (tmp_len <= max_len)
+                               {
+                               /* One of the other wNAFs is at least as long
+                                * as the wNAF belonging to the generator,
+                                * so wNAF splitting will not buy us anything. */
+
+                               numblocks = 1;
+                               totalnum = num + 1; /* don't use wNAF splitting */
+                               wNAF[num] = tmp_wNAF;
+                               wNAF[num + 1] = NULL;
+                               wNAF_len[num] = tmp_len;
+                               if (tmp_len > max_len)
+                                       max_len = tmp_len;
+                               /* pre_comp->points starts with the points that we need here: */
+                               val_sub[num] = pre_comp->points;
+                               }
+                       else
+                               {
+                               /* don't include tmp_wNAF directly into wNAF array
+                                * - use wNAF splitting and include the blocks */
+
+                               signed char *pp;
+                               EC_POINT **tmp_points;
+                               
+                               if (tmp_len < numblocks * blocksize)
+                                       {
+                                       /* possibly we can do with fewer blocks than estimated */
+                                       numblocks = (tmp_len + blocksize - 1) / blocksize;
+                                       if (numblocks > pre_comp->numblocks)
+                                               {
+                                               ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
+                                               goto err;
+                                               }
+                                       totalnum = num + numblocks;
+                                       }
+                               
+                               /* split wNAF in 'numblocks' parts */
+                               pp = tmp_wNAF;
+                               tmp_points = pre_comp->points;
+
+                               for (i = num; i < totalnum; i++)
+                                       {
+                                       if (i < totalnum - 1)
+                                               {
+                                               wNAF_len[i] = blocksize;
+                                               if (tmp_len < blocksize)
+                                                       {
+                                                       ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
+                                                       goto err;
+                                                       }
+                                               tmp_len -= blocksize;
+                                               }
+                                       else
+                                               /* last block gets whatever is left
+                                                * (this could be more or less than 'blocksize'!) */
+                                               wNAF_len[i] = tmp_len;
+                                       
+                                       wNAF[i + 1] = NULL;
+                                       wNAF[i] = OPENSSL_malloc(wNAF_len[i]);
+                                       if (wNAF[i] == NULL)
+                                               {
+                                               ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
+                                               OPENSSL_free(tmp_wNAF);
+                                               goto err;
+                                               }
+                                       memcpy(wNAF[i], pp, wNAF_len[i]);
+                                       if (wNAF_len[i] > max_len)
+                                               max_len = wNAF_len[i];
+
+                                       if (*tmp_points == NULL)
+                                               {
+                                               ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
+                                               OPENSSL_free(tmp_wNAF);
+                                               goto err;
+                                               }
+                                       val_sub[i] = tmp_points;
+                                       tmp_points += pre_points_per_block;
+                                       pp += blocksize;
+                                       }
+                               OPENSSL_free(tmp_wNAF);
+                               }
+                       }
                }
 
-       /* all precomputed points go into a single array 'val',
-        * 'val_sub[i]' is a pointer to the subarray for the i-th point */
+       /* All points we precompute now go into a single array 'val'.
+        * 'val_sub[i]' is a pointer to the subarray for the i-th point,
+        * or to a subarray of 'pre_comp->points' if we already have precomputation. */
        val = OPENSSL_malloc((num_val + 1) * sizeof val[0]);
-       if (val == NULL) goto err;
+       if (val == NULL)
+               {
+               ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
+               goto err;
+               }
        val[num_val] = NULL; /* pivot element */
 
-       val_sub = OPENSSL_malloc(totalnum * sizeof val_sub[0]);
-       if (val_sub == NULL) goto err;
-
        /* allocate points for precomputation */
        v = val;
-       for (i = 0; i < totalnum; i++)
+       for (i = 0; i < num + num_scalar; i++)
                {
                val_sub[i] = v;
                for (j = 0; j < (1u << (wsize[i] - 1)); j++)
@@ -306,15 +613,8 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
                goto err;
                }
 
-       if (ctx == NULL)
-               {
-               ctx = new_ctx = BN_CTX_new();
-               if (ctx == NULL)
-                       goto err;
-               }
-       
-       tmp = EC_POINT_new(group);
-       if (tmp == NULL) goto err;
+       if (!(tmp = EC_POINT_new(group)))
+               goto err;
 
        /* prepare precomputed values:
         *    val_sub[i][0] :=     points[i]
@@ -322,7 +622,7 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
         *    val_sub[i][2] := 5 * points[i]
         *    ...
         */
-       for (i = 0; i < totalnum; i++)
+       for (i = 0; i < num + num_scalar; i++)
                {
                if (i < num)
                        {
@@ -341,16 +641,11 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
                                if (!EC_POINT_add(group, val_sub[i][j], val_sub[i][j - 1], tmp, ctx)) goto err;
                                }
                        }
-
-               wNAF[i + 1] = NULL; /* make sure we always have a pivot */
-               wNAF[i] = compute_wNAF((i < num ? scalars[i] : scalar), wsize[i], &wNAF_len[i]);
-               if (wNAF[i] == NULL) goto err;
-               if (wNAF_len[i] > max_len)
-                       max_len = wNAF_len[i];
                }
 
 #if 1 /* optional; EC_window_bits_for_scalar_size assumes we do this step */
-       if (!EC_POINTs_make_affine(group, num_val, val, ctx)) goto err;
+       if (!EC_POINTs_make_affine(group, num_val, val, ctx))
+               goto err;
 #endif
 
        r_is_at_infinity = 1;
@@ -446,86 +741,198 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
        }
 
 
-/* Generic multiplication method.
- * If group->meth does not provide a multiplication method, default to ec_wNAF_mul;
- * otherwise use the group->meth's multiplication.
+/* ec_wNAF_precompute_mult()
+ * creates an EC_PRE_COMP object with preprecomputed multiples of the generator
+ * for use with wNAF splitting as implemented in ec_wNAF_mul().
+ * 
+ * 'pre_comp->points' is an array of multiples of the generator
+ * of the following form:
+ * points[0] =     generator;
+ * points[1] = 3 * generator;
+ * ...
+ * points[2^(w-1)-1] =     (2^(w-1)-1) * generator;
+ * points[2^(w-1)]   =     2^blocksize * generator;
+ * points[2^(w-1)+1] = 3 * 2^blocksize * generator;
+ * ...
+ * points[2^(w-1)*(numblocks-1)-1] = (2^(w-1)) *  2^(blocksize*(numblocks-2)) * generator
+ * points[2^(w-1)*(numblocks-1)]   =              2^(blocksize*(numblocks-1)) * generator
+ * ...
+ * points[2^(w-1)*numblocks-1]     = (2^(w-1)) *  2^(blocksize*(numblocks-1)) * generator
+ * points[2^(w-1)*numblocks]       = NULL
  */
-int EC_POINTs_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
-       size_t num, const EC_POINT *points[], const BIGNUM *scalars[], BN_CTX *ctx)
-       {
-       if (group->meth->mul == 0)
-               return ec_wNAF_mul(group, r, scalar, num, points, scalars, ctx);
-       else
-               return group->meth->mul(group, r, scalar, num, points, scalars, ctx);
-       }
-
-
-int EC_POINT_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *g_scalar, const EC_POINT *point, const BIGNUM *p_scalar, BN_CTX *ctx)
-       {
-       const EC_POINT *points[1];
-       const BIGNUM *scalars[1];
-
-       points[0] = point;
-       scalars[0] = p_scalar;
-
-       return EC_POINTs_mul(group, r, g_scalar, (point != NULL && p_scalar != NULL), points, scalars, ctx);
-       }
-
-
 int ec_wNAF_precompute_mult(EC_GROUP *group, BN_CTX *ctx)
        {
        const EC_POINT *generator;
+       EC_POINT *tmp_point = NULL, *base = NULL, **var;
        BN_CTX *new_ctx = NULL;
        BIGNUM *order;
+       size_t i, bits, w, pre_points_per_block, blocksize, numblocks, num;
+       EC_POINT **points = NULL;
+       EC_PRE_COMP *pre_comp;
        int ret = 0;
 
+       /* if there is an old EC_PRE_COMP object, throw it away */
+       EC_EX_DATA_free_data(&group->extra_data, ec_pre_comp_dup, ec_pre_comp_free, ec_pre_comp_clear_free);
+
+       if ((pre_comp = ec_pre_comp_new(group)) == NULL)
+               return 0;
+
        generator = EC_GROUP_get0_generator(group);
        if (generator == NULL)
                {
                ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, EC_R_UNDEFINED_GENERATOR);
-               return 0;
+               goto err;
                }
 
        if (ctx == NULL)
                {
                ctx = new_ctx = BN_CTX_new();
                if (ctx == NULL)
-                       return 0;
+                       goto err;
                }
        
        BN_CTX_start(ctx);
        order = BN_CTX_get(ctx);
        if (order == NULL) goto err;
        
-       if (!EC_GROUP_get_order(group, order, ctx)) return 0;
+       if (!EC_GROUP_get_order(group, order, ctx)) goto err;           
        if (BN_is_zero(order))
                {
                ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, EC_R_UNKNOWN_ORDER);
                goto err;
                }
 
-       /* TODO */
+       bits = BN_num_bits(order);
+       /* The following parameters mean we precompute (approximately)
+        * one point per bit.
+        *
+        * TBD: The combination  8, 4  is perfect for 160 bits; for other
+        * bit lengths, other parameter combinations might provide better
+        * efficiency.
+        */
+       blocksize = 8;
+       w = 4;
+       if (EC_window_bits_for_scalar_size(bits) > w)
+               {
+               /* let's not make the window too small ... */
+               w = EC_window_bits_for_scalar_size(bits);
+               }
 
-       ret = 1;
+       numblocks = (bits + blocksize - 1) / blocksize; /* max. number of blocks to use for wNAF splitting */
+       
+       pre_points_per_block = 1u << (w - 1);
+       num = pre_points_per_block * numblocks; /* number of points to compute and store */
+
+       points = OPENSSL_malloc(sizeof (EC_POINT*)*(num + 1));
+       if (!points)
+               {
+               ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
+               goto err;
+               }
+
+       var = points;
+       var[num] = NULL; /* pivot */
+       for (i = 0; i < num; i++)
+               {
+               if ((var[i] = EC_POINT_new(group)) == NULL)
+                       {
+                       ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
+                       goto err;
+                       }
+               }
+
+       if (!(tmp_point = EC_POINT_new(group)) || !(base = EC_POINT_new(group)))
+               {
+               ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
+               goto err;
+               }       
+       
+       if (!EC_POINT_copy(base, generator))
+               goto err;
+       
+       /* do the precomputation */
+       for (i = 0; i < numblocks; i++)
+               {
+               size_t j;
+
+               if (!EC_POINT_dbl(group, tmp_point, base, ctx))
+                       goto err;
+
+               if (!EC_POINT_copy(*var++, base))
+                       goto err;
+
+               for (j = 1; j < pre_points_per_block; j++, var++)
+                       {
+                       /* calculate odd multiples of the current base point */
+                       if (!EC_POINT_add(group, *var, tmp_point, *(var - 1), ctx))
+                               goto err;
+                       }
+
+               if (i < numblocks - 1)
+                       {
+                       /* get the next base (multiply current one by 2^blocksize) */
+                       size_t k;
+
+                       if (blocksize <= 2)
+                               {
+                               ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_INTERNAL_ERROR);
+                               goto err;
+                               }                               
+
+                       if (!EC_POINT_dbl(group, base, tmp_point, ctx))
+                               goto err;
+                       for (k = 2; k < blocksize; k++)
+                               {
+                               if (!EC_POINT_dbl(group,base,base,ctx))
+                                       goto err;
+                               }
+                       }
+               }
+
+       if (!EC_POINTs_make_affine(group, num, points, ctx))
+               goto err;
        
+       pre_comp->group = group;
+       pre_comp->blocksize = blocksize;
+       pre_comp->numblocks = numblocks;
+       pre_comp->w = w;
+       pre_comp->points = points;
+       points = NULL;
+       pre_comp->num = num;
+
+       if (!EC_EX_DATA_set_data(&group->extra_data, pre_comp,
+               ec_pre_comp_dup, ec_pre_comp_free, ec_pre_comp_clear_free))
+               goto err;
+       pre_comp = NULL;
+
+       ret = 1;
  err:
-       BN_CTX_end(ctx);
+       if (ctx != NULL)
+               BN_CTX_end(ctx);
        if (new_ctx != NULL)
                BN_CTX_free(new_ctx);
+       if (pre_comp)
+               ec_pre_comp_free(pre_comp);
+       if (points)
+               {
+               EC_POINT **p;
+
+               for (p = points; *p != NULL; p++)
+                       EC_POINT_free(*p);
+               OPENSSL_free(points);
+               }
+       if (tmp_point)
+               EC_POINT_free(tmp_point);
+       if (base)
+               EC_POINT_free(base);
        return ret;
        }
 
 
-/* Generic multiplicaiton precomputation method.
- * If group->meth does not provide a multiplication method, default to ec_wNAF_mul and do its
- * precomputation; otherwise use the group->meth's precomputation if it exists.
- */
-int EC_GROUP_precompute_mult(EC_GROUP *group, BN_CTX *ctx)
+int ec_wNAF_have_precompute_mult(const EC_GROUP *group)
        {
-       if (group->meth->mul == 0)
-               return ec_wNAF_precompute_mult(group, ctx);
-       else if (group->meth->precompute_mult != 0)
-               return group->meth->precompute_mult(group, ctx);
-       else
+       if (EC_EX_DATA_get_data(group->extra_data, ec_pre_comp_dup, ec_pre_comp_free, ec_pre_comp_clear_free) != NULL)
                return 1;
+       else
+               return 0;
        }