ecmult_gen: Simplify ecmult_gen context after making table static

This is a backwards-compatible API change: Before this commit, a context
initialized for signing was required to call functions that rely on
ecmult_gen. After this commit, this is no longer necessary because the
static ecmult_gen table is always present. In practice this means that
the corresponding functions will just work instead of calling the
illegal callback when given a context which is not (officially)
initialized for signing.

This is in line with 6815761, which made the analogous change with
respect to ecmult and contexts initialized for signing. But as opposed
to 681571, which removed the ecmult context entirely, we cannot remove
the ecmult_gen context entirely because it is still used for random
blinding. Moreover, since the secp256k1_context_no_precomp context is
const and cannot meaningfully support random blinding, we refrain (for
now) from changing its API, i.e., the illegal callback will still be
called when trying to use ecmult_gen operations with the static
secp256k1_context_no_precomp context.

src/ecmult_gen.h

@@ -18,28 +18,16 @@
 #define ECMULT_GEN_PREC_N (256 / ECMULT_GEN_PREC_B)
 
 typedef struct {
-    /* For accelerating the computation of a*G:
-     * To harden against timing attacks, use the following mechanism:
-     * * Break up the multiplicand into groups of PREC_B bits, called n_0, n_1, n_2, ..., n_(PREC_N-1).
-     * * Compute sum(n_i * (PREC_G)^i * G + U_i, i=0 ... PREC_N-1), where:
-     *   * U_i = U * 2^i, for i=0 ... PREC_N-2
-     *   * U_i = U * (1-2^(PREC_N-1)), for i=PREC_N-1
-     *   where U is a point with no known corresponding scalar. Note that sum(U_i, i=0 ... PREC_N-1) = 0.
-     * For each i, and each of the PREC_G possible values of n_i, (n_i * (PREC_G)^i * G + U_i) is
-     * precomputed (call it prec(i, n_i)). The formula now becomes sum(prec(i, n_i), i=0 ... PREC_N-1).
-     * None of the resulting prec group elements have a known scalar, and neither do any of
-     * the intermediate sums while computing a*G.
-     */
-    secp256k1_ge_storage (*prec)[ECMULT_GEN_PREC_N][ECMULT_GEN_PREC_G]; /* prec[j][i] = (PREC_G)^j * i * G + U_i */
-    secp256k1_scalar blind;
-    secp256k1_gej initial;
+    /* Whether the context has been built. */
+    int built;
+
+    /* Blinding values used when computing (n-b)G + bG. */
+    secp256k1_scalar blind; /* -b */
+    secp256k1_gej initial;  /* bG */
 } secp256k1_ecmult_gen_context;
 
-static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context* ctx);
-static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context* ctx, void **prealloc);
-static void secp256k1_ecmult_gen_context_finalize_memcpy(secp256k1_ecmult_gen_context *dst, const secp256k1_ecmult_gen_context* src);
+static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context* ctx);
 static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context* ctx);
-static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context* ctx);
 
 /** Multiply with the generator: R = a*G */
 static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context* ctx, secp256k1_gej *r, const secp256k1_scalar *a);

src/ecmult_gen_impl.h

@@ -14,35 +14,34 @@
 #include "hash_impl.h"
 #include "ecmult_static_context.h"
 
-static const size_t SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE = 0;
-
-static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context *ctx) {
-    ctx->prec = NULL;
-}
-
-static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context *ctx, void **prealloc) {
-    if (ctx->prec != NULL) {
-        return;
-    }
-    (void)prealloc;
-    ctx->prec = (secp256k1_ge_storage (*)[ECMULT_GEN_PREC_N][ECMULT_GEN_PREC_G])secp256k1_ecmult_static_context;
+static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context *ctx) {
     secp256k1_ecmult_gen_blind(ctx, NULL);
+    ctx->built = 1;
 }
 
 static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context* ctx) {
-    return ctx->prec != NULL;
-}
-
-static void secp256k1_ecmult_gen_context_finalize_memcpy(secp256k1_ecmult_gen_context *dst, const secp256k1_ecmult_gen_context *src) {
-    (void)dst, (void)src;
+    return ctx->built;
 }
 
 static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context *ctx) {
+    ctx->built = 0;
     secp256k1_scalar_clear(&ctx->blind);
     secp256k1_gej_clear(&ctx->initial);
-    ctx->prec = NULL;
 }
 
+/* For accelerating the computation of a*G:
+ * To harden against timing attacks, use the following mechanism:
+ * * Break up the multiplicand into groups of PREC_B bits, called n_0, n_1, n_2, ..., n_(PREC_N-1).
+ * * Compute sum(n_i * (PREC_G)^i * G + U_i, i=0 ... PREC_N-1), where:
+ *   * U_i = U * 2^i, for i=0 ... PREC_N-2
+ *   * U_i = U * (1-2^(PREC_N-1)), for i=PREC_N-1
+ *   where U is a point with no known corresponding scalar. Note that sum(U_i, i=0 ... PREC_N-1) = 0.
+ * For each i, and each of the PREC_G possible values of n_i, (n_i * (PREC_G)^i * G + U_i) is
+ * precomputed (call it prec(i, n_i)). The formula now becomes sum(prec(i, n_i), i=0 ... PREC_N-1).
+ * None of the resulting prec group elements have a known scalar, and neither do any of
+ * the intermediate sums while computing a*G.
+ * The prec values are stored in secp256k1_ecmult_gen_prec_table[j][i] = (PREC_G)^j * i * G + U_i.
+ */
 static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context *ctx, secp256k1_gej *r, const secp256k1_scalar *gn) {
     secp256k1_ge add;
     secp256k1_ge_storage adds;
@@ -67,7 +66,7 @@ static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context *ctx, secp25
              *    by Dag Arne Osvik, Adi Shamir, and Eran Tromer
              *    (https://www.tau.ac.il/~tromer/papers/cache.pdf)
              */
-            secp256k1_ge_storage_cmov(&adds, &(*ctx->prec)[j][i], i == bits);
+            secp256k1_ge_storage_cmov(&adds, &secp256k1_ecmult_gen_prec_table[j][i], i == bits);
         }
         secp256k1_ge_from_storage(&add, &adds);
         secp256k1_gej_add_ge(r, r, &add);

src/gen_context.c

@@ -56,7 +56,7 @@ int main(int argc, char **argv) {
     fprintf(fp, "#if ECMULT_GEN_PREC_N != %d || ECMULT_GEN_PREC_G != %d\n", ECMULT_GEN_PREC_N, ECMULT_GEN_PREC_G);
     fprintf(fp, "   #error configuration mismatch, invalid ECMULT_GEN_PREC_N, ECMULT_GEN_PREC_G. Try deleting ecmult_static_context.h before the build.\n");
     fprintf(fp, "#endif\n");
-    fprintf(fp, "static const secp256k1_ge_storage secp256k1_ecmult_static_context[ECMULT_GEN_PREC_N][ECMULT_GEN_PREC_G] = {\n");
+    fprintf(fp, "static const secp256k1_ge_storage secp256k1_ecmult_gen_prec_table[ECMULT_GEN_PREC_N][ECMULT_GEN_PREC_G] = {\n");
 
     table = checked_malloc(&default_error_callback, ECMULT_GEN_PREC_TABLE_SIZE);
     secp256k1_ecmult_gen_create_prec_table(table);

src/modules/extrakeys/tests_impl.h

@@ -359,25 +359,32 @@ void test_keypair(void) {
     secp256k1_context *none = api_test_context(SECP256K1_CONTEXT_NONE, &ecount);
     secp256k1_context *sign = api_test_context(SECP256K1_CONTEXT_SIGN, &ecount);
     secp256k1_context *verify = api_test_context(SECP256K1_CONTEXT_VERIFY, &ecount);
+    secp256k1_context *sttc = secp256k1_context_clone(secp256k1_context_no_precomp);
+    secp256k1_context_set_error_callback(sttc, counting_illegal_callback_fn, &ecount);
+    secp256k1_context_set_illegal_callback(sttc, counting_illegal_callback_fn, &ecount);
 
     CHECK(sizeof(zeros96) == sizeof(keypair));
     memset(overflows, 0xFF, sizeof(overflows));
 
     /* Test keypair_create */
     ecount = 0;
     secp256k1_testrand256(sk);
-    CHECK(secp256k1_keypair_create(none, &keypair, sk) == 0);
-    CHECK(secp256k1_memcmp_var(zeros96, &keypair, sizeof(keypair)) == 0);
+    CHECK(secp256k1_keypair_create(none, &keypair, sk) == 1);
+    CHECK(secp256k1_memcmp_var(zeros96, &keypair, sizeof(keypair)) != 0);
+    CHECK(ecount == 0);
+    CHECK(secp256k1_keypair_create(verify, &keypair, sk) == 1);
+    CHECK(secp256k1_memcmp_var(zeros96, &keypair, sizeof(keypair)) != 0);
+    CHECK(ecount == 0);
+    CHECK(secp256k1_keypair_create(sign, NULL, sk) == 0);
     CHECK(ecount == 1);
-    CHECK(secp256k1_keypair_create(verify, &keypair, sk) == 0);
+    CHECK(secp256k1_keypair_create(sign, &keypair, NULL) == 0);
     CHECK(secp256k1_memcmp_var(zeros96, &keypair, sizeof(keypair)) == 0);
     CHECK(ecount == 2);
     CHECK(secp256k1_keypair_create(sign, &keypair, sk) == 1);
-    CHECK(secp256k1_keypair_create(sign, NULL, sk) == 0);
-    CHECK(ecount == 3);
-    CHECK(secp256k1_keypair_create(sign, &keypair, NULL) == 0);
+    CHECK(ecount == 2);
+    CHECK(secp256k1_keypair_create(sttc, &keypair, sk) == 0);
     CHECK(secp256k1_memcmp_var(zeros96, &keypair, sizeof(keypair)) == 0);
-    CHECK(ecount == 4);
+    CHECK(ecount == 3);
 
     /* Invalid secret key */
     CHECK(secp256k1_keypair_create(sign, &keypair, zeros96) == 0);
@@ -459,6 +466,7 @@ void test_keypair(void) {
     secp256k1_context_destroy(none);
     secp256k1_context_destroy(sign);
     secp256k1_context_destroy(verify);
+    secp256k1_context_destroy(sttc);
 }
 
 void test_keypair_add(void) {

src/modules/recovery/tests_impl.h

@@ -34,6 +34,7 @@ void test_ecdsa_recovery_api(void) {
     secp256k1_context *sign = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
     secp256k1_context *vrfy = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY);
     secp256k1_context *both = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
+    secp256k1_context *sttc = secp256k1_context_clone(secp256k1_context_no_precomp);
     secp256k1_pubkey pubkey;
     secp256k1_pubkey recpubkey;
     secp256k1_ecdsa_signature normal_sig;
@@ -53,40 +54,44 @@ void test_ecdsa_recovery_api(void) {
     secp256k1_context_set_error_callback(sign, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_error_callback(vrfy, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_error_callback(both, counting_illegal_callback_fn, &ecount);
+    secp256k1_context_set_error_callback(sttc, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(none, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(sign, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(vrfy, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(both, counting_illegal_callback_fn, &ecount);
+    secp256k1_context_set_illegal_callback(sttc, counting_illegal_callback_fn, &ecount);
 
     /* Construct and verify corresponding public key. */
     CHECK(secp256k1_ec_seckey_verify(ctx, privkey) == 1);
     CHECK(secp256k1_ec_pubkey_create(ctx, &pubkey, privkey) == 1);
 
     /* Check bad contexts and NULLs for signing */
     ecount = 0;
-    CHECK(secp256k1_ecdsa_sign_recoverable(none, &recsig, message, privkey, NULL, NULL) == 0);
-    CHECK(ecount == 1);
+    CHECK(secp256k1_ecdsa_sign_recoverable(none, &recsig, message, privkey, NULL, NULL) == 1);
+    CHECK(ecount == 0);
     CHECK(secp256k1_ecdsa_sign_recoverable(sign, &recsig, message, privkey, NULL, NULL) == 1);
-    CHECK(ecount == 1);
-    CHECK(secp256k1_ecdsa_sign_recoverable(vrfy, &recsig, message, privkey, NULL, NULL) == 0);
-    CHECK(ecount == 2);
+    CHECK(ecount == 0);
+    CHECK(secp256k1_ecdsa_sign_recoverable(vrfy, &recsig, message, privkey, NULL, NULL) == 1);
+    CHECK(ecount == 0);
     CHECK(secp256k1_ecdsa_sign_recoverable(both, &recsig, message, privkey, NULL, NULL) == 1);
-    CHECK(ecount == 2);
+    CHECK(ecount == 0);
     CHECK(secp256k1_ecdsa_sign_recoverable(both, NULL, message, privkey, NULL, NULL) == 0);
-    CHECK(ecount == 3);
+    CHECK(ecount == 1);
     CHECK(secp256k1_ecdsa_sign_recoverable(both, &recsig, NULL, privkey, NULL, NULL) == 0);
-    CHECK(ecount == 4);
+    CHECK(ecount == 2);
     CHECK(secp256k1_ecdsa_sign_recoverable(both, &recsig, message, NULL, NULL, NULL) == 0);
-    CHECK(ecount == 5);
+    CHECK(ecount == 3);
+    CHECK(secp256k1_ecdsa_sign_recoverable(sttc, &recsig, message, privkey, NULL, NULL) == 0);
+    CHECK(ecount == 4);
     /* This will fail or succeed randomly, and in either case will not ARG_CHECK failure */
     secp256k1_ecdsa_sign_recoverable(both, &recsig, message, privkey, recovery_test_nonce_function, NULL);
-    CHECK(ecount == 5);
+    CHECK(ecount == 4);
     /* These will all fail, but not in ARG_CHECK way */
     CHECK(secp256k1_ecdsa_sign_recoverable(both, &recsig, message, zero_privkey, NULL, NULL) == 0);
     CHECK(secp256k1_ecdsa_sign_recoverable(both, &recsig, message, over_privkey, NULL, NULL) == 0);
     /* This one will succeed. */
     CHECK(secp256k1_ecdsa_sign_recoverable(both, &recsig, message, privkey, NULL, NULL) == 1);
-    CHECK(ecount == 5);
+    CHECK(ecount == 4);
 
     /* Check signing with a goofy nonce function */
 
@@ -145,6 +150,7 @@ void test_ecdsa_recovery_api(void) {
     secp256k1_context_destroy(sign);
     secp256k1_context_destroy(vrfy);
     secp256k1_context_destroy(both);
+    secp256k1_context_destroy(sttc);
 }
 
 void test_ecdsa_recovery_end_to_end(void) {

src/modules/schnorrsig/tests_impl.h

@@ -132,16 +132,19 @@ void test_schnorrsig_api(void) {
     secp256k1_context *sign = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
     secp256k1_context *vrfy = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY);
     secp256k1_context *both = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
+    secp256k1_context *sttc = secp256k1_context_clone(secp256k1_context_no_precomp);
     int ecount;
 
     secp256k1_context_set_error_callback(none, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_error_callback(sign, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_error_callback(vrfy, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_error_callback(both, counting_illegal_callback_fn, &ecount);
+    secp256k1_context_set_error_callback(sttc, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(none, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(sign, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(vrfy, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(both, counting_illegal_callback_fn, &ecount);
+    secp256k1_context_set_illegal_callback(sttc, counting_illegal_callback_fn, &ecount);
 
     secp256k1_testrand256(sk1);
     secp256k1_testrand256(sk2);
@@ -157,42 +160,46 @@ void test_schnorrsig_api(void) {
 
     /** main test body **/
     ecount = 0;
-    CHECK(secp256k1_schnorrsig_sign(none, sig, msg, &keypairs[0], NULL) == 0);
-    CHECK(ecount == 1);
-    CHECK(secp256k1_schnorrsig_sign(vrfy, sig, msg, &keypairs[0], NULL) == 0);
-    CHECK(ecount == 2);
+    CHECK(secp256k1_schnorrsig_sign(none, sig, msg, &keypairs[0], NULL) == 1);
+    CHECK(ecount == 0);
+    CHECK(secp256k1_schnorrsig_sign(vrfy, sig, msg, &keypairs[0], NULL) == 1);
+    CHECK(ecount == 0);
     CHECK(secp256k1_schnorrsig_sign(sign, sig, msg, &keypairs[0], NULL) == 1);
-    CHECK(ecount == 2);
+    CHECK(ecount == 0);
     CHECK(secp256k1_schnorrsig_sign(sign, NULL, msg, &keypairs[0], NULL) == 0);
-    CHECK(ecount == 3);
+    CHECK(ecount == 1);
     CHECK(secp256k1_schnorrsig_sign(sign, sig, NULL, &keypairs[0], NULL) == 0);
-    CHECK(ecount == 4);
+    CHECK(ecount == 2);
     CHECK(secp256k1_schnorrsig_sign(sign, sig, msg, NULL, NULL) == 0);
-    CHECK(ecount == 5);
+    CHECK(ecount == 3);
     CHECK(secp256k1_schnorrsig_sign(sign, sig, msg, &invalid_keypair, NULL) == 0);
-    CHECK(ecount == 6);
+    CHECK(ecount == 4);
+    CHECK(secp256k1_schnorrsig_sign(sttc, sig, msg, &keypairs[0], NULL) == 0);
+    CHECK(ecount == 5);
 
     ecount = 0;
-    CHECK(secp256k1_schnorrsig_sign_custom(none, sig, msg, sizeof(msg), &keypairs[0], &extraparams) == 0);
-    CHECK(ecount == 1);
-    CHECK(secp256k1_schnorrsig_sign_custom(vrfy, sig, msg, sizeof(msg), &keypairs[0], &extraparams) == 0);
-    CHECK(ecount == 2);
+    CHECK(secp256k1_schnorrsig_sign_custom(none, sig, msg, sizeof(msg), &keypairs[0], &extraparams) == 1);
+    CHECK(ecount == 0);
+    CHECK(secp256k1_schnorrsig_sign_custom(vrfy, sig, msg, sizeof(msg), &keypairs[0], &extraparams) == 1);
+    CHECK(ecount == 0);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, sig, msg, sizeof(msg), &keypairs[0], &extraparams) == 1);
-    CHECK(ecount == 2);
+    CHECK(ecount == 0);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, NULL, msg, sizeof(msg), &keypairs[0], &extraparams) == 0);
-    CHECK(ecount == 3);
+    CHECK(ecount == 1);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, sig, NULL, sizeof(msg), &keypairs[0], &extraparams) == 0);
-    CHECK(ecount == 4);
+    CHECK(ecount == 2);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, sig, NULL, 0, &keypairs[0], &extraparams) == 1);
-    CHECK(ecount == 4);
+    CHECK(ecount == 2);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, sig, msg, sizeof(msg), NULL, &extraparams) == 0);
-    CHECK(ecount == 5);
+    CHECK(ecount == 3);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, sig, msg, sizeof(msg), &invalid_keypair, &extraparams) == 0);
-    CHECK(ecount == 6);
+    CHECK(ecount == 4);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, sig, msg, sizeof(msg), &keypairs[0], NULL) == 1);
-    CHECK(ecount == 6);
+    CHECK(ecount == 4);
     CHECK(secp256k1_schnorrsig_sign_custom(sign, sig, msg, sizeof(msg), &keypairs[0], &invalid_extraparams) == 0);
-    CHECK(ecount == 7);
+    CHECK(ecount == 5);
+    CHECK(secp256k1_schnorrsig_sign_custom(sttc, sig, msg, sizeof(msg), &keypairs[0], &extraparams) == 0);
+    CHECK(ecount == 6);
 
     ecount = 0;
     CHECK(secp256k1_schnorrsig_sign(sign, sig, msg, &keypairs[0], NULL) == 1);
@@ -217,6 +224,7 @@ void test_schnorrsig_api(void) {
     secp256k1_context_destroy(sign);
     secp256k1_context_destroy(vrfy);
     secp256k1_context_destroy(both);
+    secp256k1_context_destroy(sttc);
 }
 
 /* Checks that hash initialized by secp256k1_schnorrsig_sha256_tagged has the

src/secp256k1.c

@@ -98,18 +98,12 @@ size_t secp256k1_context_preallocated_size(unsigned int flags) {
             return 0;
     }
 
-    if (flags & SECP256K1_FLAGS_BIT_CONTEXT_SIGN) {
-        ret += SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE;
-    }
     return ret;
 }
 
 size_t secp256k1_context_preallocated_clone_size(const secp256k1_context* ctx) {
     size_t ret = ROUND_TO_ALIGN(sizeof(secp256k1_context));
     VERIFY_CHECK(ctx != NULL);
-    if (secp256k1_ecmult_gen_context_is_built(&ctx->ecmult_gen_ctx)) {
-        ret += SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE;
-    }
     return ret;
 }
 
@@ -131,13 +125,9 @@ secp256k1_context* secp256k1_context_preallocated_create(void* prealloc, unsigne
     ret->illegal_callback = default_illegal_callback;
     ret->error_callback = default_error_callback;
 
-    secp256k1_ecmult_gen_context_init(&ret->ecmult_gen_ctx);
-
     /* Flags have been checked by secp256k1_context_preallocated_size. */
     VERIFY_CHECK((flags & SECP256K1_FLAGS_TYPE_MASK) == SECP256K1_FLAGS_TYPE_CONTEXT);
-    if (flags & SECP256K1_FLAGS_BIT_CONTEXT_SIGN) {
-        secp256k1_ecmult_gen_context_build(&ret->ecmult_gen_ctx, &prealloc);
-    }
+    secp256k1_ecmult_gen_context_build(&ret->ecmult_gen_ctx);
     ret->declassify = !!(flags & SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY);
 
     return (secp256k1_context*) ret;
@@ -163,7 +153,6 @@ secp256k1_context* secp256k1_context_preallocated_clone(const secp256k1_context*
     prealloc_size = secp256k1_context_preallocated_clone_size(ctx);
     ret = (secp256k1_context*)prealloc;
     memcpy(ret, ctx, prealloc_size);
-    secp256k1_ecmult_gen_context_finalize_memcpy(&ret->ecmult_gen_ctx, &ctx->ecmult_gen_ctx);
     return ret;
 }