extrakeys: Init empty experimental module

Summary:
This is to prepare for xonly_pubkeys and keypairs.

This is a partial backport of secp256k1 [[bitcoin-core/secp256k1#558 | PR558]] : bitcoin-core/secp256k1@47e6618

Test Plan:
  ninja check-secp256k1

And with the module on:
  cmake -GNinja .. -DSECP256K1_ENABLE_MODULE_EXTRAKEYS=On
  ninja check-secp256k1

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7638

Author: jonasnick

CMakeLists.txt

@@ -226,6 +226,13 @@ if(SECP256K1_ENABLE_MODULE_SCHNORR)
 	list(APPEND SECP256K1_PUBLIC_HEADERS include/secp256k1_schnorr.h)
 endif()
 
+# Extrakeys module
+option(SECP256K1_ENABLE_MODULE_EXTRAKEYS "Build libsecp256k1's Extrakeys module" OFF)
+if(SECP256K1_ENABLE_MODULE_EXTRAKEYS)
+	set(ENABLE_MODULE_EXTRAKEYS 1)
+	list(APPEND SECP256K1_PUBLIC_HEADERS include/secp256k1_extrakeys.h)
+endif()
+
 # External default callbacks
 option(SECP256K1_ENABLE_EXTERNAL_DEFAULT_CALLBACKS "Enable external default callbacks" OFF)
 if(SECP256K1_ENABLE_EXTERNAL_DEFAULT_CALLBACKS)

Makefile.am

@@ -197,3 +197,7 @@ endif
 if ENABLE_MODULE_SCHNORR
 include src/modules/schnorr/Makefile.am.include
 endif
+
+if ENABLE_MODULE_EXTRAKEYS
+include src/modules/extrakeys/Makefile.am.include
+endif

configure.ac

@@ -146,6 +146,11 @@ AC_ARG_ENABLE(module_schnorr,
     [enable_module_schnorr=$enableval],
     [enable_module_schnorr=yes])
 
+AC_ARG_ENABLE(module_extrakeys,
+    AS_HELP_STRING([--enable-module-extrakeys],[enable extrakeys module (experimental)]),
+    [enable_module_extrakeys=$enableval],
+    [enable_module_extrakeys=no])
+
 AC_ARG_ENABLE(external_default_callbacks,
     AS_HELP_STRING([--enable-external-default-callbacks],[enable external default callback functions [default=no]]),
     [use_external_default_callbacks=$enableval],
@@ -481,6 +486,10 @@ if test x"$enable_module_schnorr" = x"yes"; then
   AC_DEFINE(ENABLE_MODULE_SCHNORR, 1, [Define this symbol to enable the Schnorr signature module])
 fi
 
+if test x"$enable_module_extrakeys" = x"yes"; then
+  AC_DEFINE(ENABLE_MODULE_EXTRAKEYS, 1, [Define this symbol to enable the extrakeys module])
+fi
+
 if test x"$use_external_asm" = x"yes"; then
   AC_DEFINE(USE_EXTERNAL_ASM, 1, [Define this symbol if an external (non-inline) assembly implementation is used])
 fi
@@ -494,6 +503,7 @@ if test x"$enable_experimental" = x"yes"; then
   AC_MSG_NOTICE([WARNING: experimental build])
   AC_MSG_NOTICE([Experimental features do not have stable APIs or properties, and may not be safe for production use.])
   AC_MSG_NOTICE([Building ECDH module: $enable_module_ecdh])
+  AC_MSG_NOTICE([Building extrakeys module: $enable_module_extrakeys])
   AC_MSG_NOTICE([******])
 else
   if test x"$enable_module_ecdh" = x"yes"; then
@@ -502,6 +512,9 @@ else
   if test x"$enable_module_multiset" = x"yes"; then
     AC_MSG_ERROR([Multiset module is experimental. Use --enable-experimental to allow.])
   fi
+  if test x"$enable_module_extrakeys" = x"yes"; then
+    AC_MSG_ERROR([extrakeys module is experimental. Use --enable-experimental to allow.])
+  fi
   if test x"$set_asm" = x"arm"; then
     AC_MSG_ERROR([ARM assembly optimization is experimental. Use --enable-experimental to allow.])
   fi
@@ -521,6 +534,7 @@ AM_CONDITIONAL([USE_BENCHMARK], [test x"$use_benchmark" = x"yes"])
 AM_CONDITIONAL([USE_ECMULT_STATIC_PRECOMPUTATION], [test x"$set_precomp" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_ECDH], [test x"$enable_module_ecdh" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_MULTISET], [test x"$enable_module_multiset" = x"yes"])
+AM_CONDITIONAL([ENABLE_MODULE_EXTRAKEYS], [test x"$enable_module_extrakeys" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_RECOVERY], [test x"$enable_module_recovery" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_SCHNORR], [test x"$enable_module_schnorr" = x"yes"])
 AM_CONDITIONAL([USE_JNI], [test x"$use_jni" = x"yes"])
@@ -546,6 +560,7 @@ echo "  module ecdh             = $enable_module_ecdh"
 echo "  module recovery         = $enable_module_recovery"
 echo "  module multiset         = $enable_module_multiset"
 echo "  module schnorr          = $enable_module_schnorr"
+echo "  module extrakeys        = $enable_module_extrakeys"
 echo
 echo "  asm                     = $set_asm"
 echo "  bignum                  = $set_bignum"

include/secp256k1_extrakeys.h

@@ -0,0 +1,14 @@
+#ifndef SECP256K1_EXTRAKEYS_H
+#define SECP256K1_EXTRAKEYS_H
+
+#include "secp256k1.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SECP256K1_EXTRAKEYS_H */

src/modules/extrakeys/Makefile.am.include

@@ -0,0 +1,3 @@
+include_HEADERS += include/secp256k1_extrakeys.h
+noinst_HEADERS += src/modules/extrakeys/tests_impl.h
+noinst_HEADERS += src/modules/extrakeys/main_impl.h

src/modules/extrakeys/main_impl.h

@@ -0,0 +1,13 @@
+/**********************************************************************
+ * Copyright (c) 2020 Jonas Nick                                      *
+ * Distributed under the MIT software license, see the accompanying   *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef _SECP256K1_MODULE_EXTRAKEYS_MAIN_
+#define _SECP256K1_MODULE_EXTRAKEYS_MAIN_
+
+#include "include/secp256k1.h"
+#include "include/secp256k1_extrakeys.h"
+
+#endif

src/modules/extrakeys/tests_impl.h

@@ -0,0 +1,16 @@
+/**********************************************************************
+ * Copyright (c) 2020 Jonas Nick                                      *
+ * Distributed under the MIT software license, see the accompanying   *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef _SECP256K1_MODULE_EXTRAKEYS_TESTS_
+#define _SECP256K1_MODULE_EXTRAKEYS_TESTS_
+
+#include "secp256k1_extrakeys.h"
+
+void run_extrakeys_tests(void) {
+    /* TODO */
+}
+
+#endif

src/secp256k1.c

@@ -751,3 +751,7 @@ int secp256k1_ec_pubkey_combine(const secp256k1_context* ctx, secp256k1_pubkey *
 #ifdef ENABLE_MODULE_SCHNORR
 # include "modules/schnorr/main_impl.h"
 #endif
+
+#ifdef ENABLE_MODULE_EXTRAKEYS
+# include "modules/extrakeys/main_impl.h"
+#endif

src/tests.c

@@ -5360,6 +5360,10 @@ void run_ecdsa_openssl(void) {
 # include "modules/schnorr/tests_impl.h"
 #endif
 
+#ifdef ENABLE_MODULE_EXTRAKEYS
+# include "modules/extrakeys/tests_impl.h"
+#endif
+
 void run_memczero_test(void) {
     unsigned char buf1[6] = {1, 2, 3, 4, 5, 6};
     unsigned char buf2[sizeof(buf1)];
@@ -5675,6 +5679,10 @@ int main(int argc, char **argv) {
     run_schnorr_tests();
 #endif
 
+#ifdef ENABLE_MODULE_EXTRAKEYS
+    run_extrakeys_tests();
+#endif
+
     /* util tests */
     run_memczero_test();