Expose ability to deep-copy a context

include/secp256k1.h

@@ -59,6 +59,14 @@ secp256k1_context_t* secp256k1_context_create(
   int flags
 ) SECP256K1_WARN_UNUSED_RESULT;
 
+/** Copies a secp256k1 context object.
+ *  Returns: a newly created context object.
+ *  In:      ctx: an existing context to copy
+ */
+secp256k1_context_t* secp256k1_context_clone(
+  const secp256k1_context_t* ctx
+) SECP256K1_WARN_UNUSED_RESULT;
+
 /** Destroy a secp256k1 context object.
  *  The context pointer may not be used afterwards.
  */

src/ecmult.h

@@ -20,6 +20,8 @@ typedef struct {
 
 static void secp256k1_ecmult_context_init(secp256k1_ecmult_context_t *ctx);
 static void secp256k1_ecmult_context_build(secp256k1_ecmult_context_t *ctx);
+static void secp256k1_ecmult_context_clone(secp256k1_ecmult_context_t *dst,
+                                           const secp256k1_ecmult_context_t *src);
 static void secp256k1_ecmult_context_clear(secp256k1_ecmult_context_t *ctx);
 static int secp256k1_ecmult_context_is_built(const secp256k1_ecmult_context_t *ctx);
 

src/ecmult_gen.h

@@ -28,6 +28,8 @@ typedef struct {
 
 static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context_t* ctx);
 static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context_t* ctx);
+static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context_t *dst,
+                                               const secp256k1_ecmult_gen_context_t* src);
 static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context_t* ctx);
 static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context_t* ctx);
 

src/ecmult_gen_impl.h

@@ -80,6 +80,16 @@ static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_cont
     return ctx->prec != NULL;
 }
 
+static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context_t *dst,
+                                               const secp256k1_ecmult_gen_context_t *src) {
+    if (src->prec == NULL) {
+        dst->prec = NULL;
+    } else {
+        dst->prec = (secp256k1_ge_storage_t (*)[64][16])checked_malloc(sizeof(*dst->prec));
+        memcpy(dst->prec, src->prec, sizeof(*dst->prec));
+    }
+}
+
 static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context_t *ctx) {
     free(ctx->prec);
     ctx->prec = NULL;

src/ecmult_impl.h

@@ -131,6 +131,26 @@ static void secp256k1_ecmult_context_build(secp256k1_ecmult_context_t *ctx) {
 #endif
 }
 
+static void secp256k1_ecmult_context_clone(secp256k1_ecmult_context_t *dst,
+                                           const secp256k1_ecmult_context_t *src) {
+    if (src->pre_g == NULL) {
+        dst->pre_g = NULL;
+    } else {
+        size_t size = sizeof((*dst->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G);
+        dst->pre_g = (secp256k1_ge_storage_t (*)[])checked_malloc(size);
+        memcpy(dst->pre_g, src->pre_g, size);
+    }
+#ifdef USE_ENDOMORPHISM
+    if (src->pre_g_128 == NULL) {
+        dst->pre_g_128 = NULL;
+    } else {
+        size_t size = sizeof((*dst->pre_g_128)[0]) * ECMULT_TABLE_SIZE(WINDOW_G);
+        dst->pre_g_128 = (secp256k1_ge_storage_t (*)[])checked_malloc(size);
+        memcpy(dst->pre_g_128, src->pre_g_128, size);
+    }
+#endif
+}
+
 static int secp256k1_ecmult_context_is_built(const secp256k1_ecmult_context_t *ctx) {
     return ctx->pre_g != NULL;
 }

src/secp256k1.c

@@ -40,6 +40,13 @@ secp256k1_context_t* secp256k1_context_create(int flags) {
     return ret;
 }
 
+secp256k1_context_t* secp256k1_context_clone(const secp256k1_context_t* ctx) {
+    secp256k1_context_t* ret = (secp256k1_context_t*)checked_malloc(sizeof(secp256k1_context_t));
+    secp256k1_ecmult_context_clone(&ret->ecmult_ctx, &ctx->ecmult_ctx);
+    secp256k1_ecmult_gen_context_clone(&ret->ecmult_gen_ctx, &ctx->ecmult_gen_ctx);
+    return ret;
+}
+
 void secp256k1_context_destroy(secp256k1_context_t* ctx) {
     secp256k1_ecmult_context_clear(&ctx->ecmult_ctx);
     secp256k1_ecmult_gen_context_clear(&ctx->ecmult_gen_ctx);

src/tests.c

@@ -103,6 +103,47 @@ void random_scalar_order(secp256k1_scalar_t *num) {
     } while(1);
 }
 
+void run_context_tests(void) {
+    secp256k1_context_t *none = secp256k1_context_create(0);
+    secp256k1_context_t *sign = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
+    secp256k1_context_t *vrfy = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY);
+    secp256k1_context_t *both = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
+
+    secp256k1_gej_t pubj;
+    secp256k1_ge_t pub;
+    secp256k1_scalar_t msg, key, nonce;
+    secp256k1_ecdsa_sig_t sig;
+
+    /*** clone and destroy all of them to make sure cloning was complete ***/
+    {
+        secp256k1_context_t *ctx_tmp;
+
+        ctx_tmp = none; none = secp256k1_context_clone(none); secp256k1_context_destroy(ctx_tmp);
+        ctx_tmp = sign; sign = secp256k1_context_clone(sign); secp256k1_context_destroy(ctx_tmp);
+        ctx_tmp = vrfy; vrfy = secp256k1_context_clone(vrfy); secp256k1_context_destroy(ctx_tmp);
+        ctx_tmp = both; both = secp256k1_context_clone(both); secp256k1_context_destroy(ctx_tmp);
+    }
+
+    /*** attempt to use them ***/
+    random_scalar_order_test(&msg);
+    random_scalar_order_test(&key);
+    secp256k1_ecmult_gen(&both->ecmult_gen_ctx, &pubj, &key);
+    secp256k1_ge_set_gej(&pub, &pubj);
+
+    /* obtain a working nonce */
+    do {
+        random_scalar_order_test(&nonce);
+    } while(!secp256k1_ecdsa_sig_sign(&both->ecmult_gen_ctx, &sig, &key, &msg, &nonce, NULL));
+
+    /* try signing */
+    CHECK(secp256k1_ecdsa_sig_sign(&sign->ecmult_gen_ctx, &sig, &key, &msg, &nonce, NULL));
+    CHECK(secp256k1_ecdsa_sig_sign(&both->ecmult_gen_ctx, &sig, &key, &msg, &nonce, NULL));
+
+    /* try verifying */
+    CHECK(secp256k1_ecdsa_sig_verify(&vrfy->ecmult_ctx, &sig, &pub, &msg));
+    CHECK(secp256k1_ecdsa_sig_verify(&both->ecmult_ctx, &sig, &pub, &msg));
+}
+
 /***** HASH TESTS *****/
 
 void run_sha256_tests(void) {
@@ -1863,6 +1904,7 @@ int main(int argc, char **argv) {
     printf("random seed = %02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x\n", seed16[0], seed16[1], seed16[2], seed16[3], seed16[4], seed16[5], seed16[6], seed16[7], seed16[8], seed16[9], seed16[10], seed16[11], seed16[12], seed16[13], seed16[14], seed16[15]);
 
     /* initialize */
+    run_context_tests();
     ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
 
     run_sha256_tests();