ecdsa_adaptor: initialize project

This commit adds the foundational configuration and building scripts
and an initial structure for the project.

Makefile.am

@@ -189,3 +189,6 @@ if ENABLE_MODULE_ECDSA_S2C
 include src/modules/ecdsa_s2c/Makefile.am.include
 endif
 
+if ENABLE_MODULE_ECDSA_ADAPTOR
+include src/modules/ecdsa_adaptor/Makefile.am.include
+endif

README.md

@@ -17,6 +17,7 @@ Features:
 * Suitable for embedded systems.
 * Optional module for public key recovery.
 * Optional module for ECDH key exchange.
+* Optional module for ECDSA adaptor signatures (experimental).
 
 Experimental features have not received enough scrutiny to satisfy the standard of quality of this library but are made available for testing and review by the community. The APIs of these features should not be considered stable.
 

configure.ac

@@ -180,6 +180,11 @@ AC_ARG_ENABLE(module_ecdsa_s2c,
     [enable_module_ecdsa_s2c=$enableval],
     [enable_module_ecdsa_s2c=no])
 
+AC_ARG_ENABLE(module_ecdsa-adaptor,
+    AS_HELP_STRING([--enable-module-ecdsa-adaptor],[enable ECDSA adaptor module [default=no]]),
+    [enable_module_ecdsa_adaptor=$enableval],
+    [enable_module_ecdsa_adaptor=no])
+
 AC_ARG_ENABLE(external_default_callbacks,
     AS_HELP_STRING([--enable-external-default-callbacks],[enable external default callback functions [default=no]]),
     [use_external_default_callbacks=$enableval],
@@ -580,6 +585,10 @@ if test x"$use_reduced_surjection_proof_size" = x"yes"; then
   AC_DEFINE(USE_REDUCED_SURJECTION_PROOF_SIZE, 1, [Define this symbol to reduce SECP256K1_SURJECTIONPROOF_MAX_N_INPUTS to 16, disabling parsing and verification])
 fi
 
+if test x"$enable_module_ecdsa_adaptor" = x"yes"; then
+  AC_DEFINE(ENABLE_MODULE_ECDSA_ADAPTOR, 1, [Define this symbol to enable the ECDSA adaptor module])
+fi
+
 ###
 ### Check for --enable-experimental if necessary
 ###
@@ -596,6 +605,7 @@ if test x"$enable_experimental" = x"yes"; then
   AC_MSG_NOTICE([Building extrakeys module: $enable_module_extrakeys])
   AC_MSG_NOTICE([Building schnorrsig module: $enable_module_schnorrsig])
   AC_MSG_NOTICE([Building ECDSA sign-to-contract module: $enable_module_ecdsa_s2c])
+  AC_MSG_NOTICE([Building ECDSA adaptor signatures module: $enable_module_ecdsa_adaptor])
   AC_MSG_NOTICE([******])
 
 
@@ -632,6 +642,9 @@ else
   if test x"$enable_module_ecdsa_s2c" = x"yes"; then
     AC_MSG_ERROR([ECDSA sign-to-contract module module is experimental. Use --enable-experimental to allow.])
   fi
+  if test x"$enable_module_ecdsa_adaptor" = x"yes"; then
+    AC_MSG_ERROR([ecdsa adaptor signatures module is experimental. Use --enable-experimental to allow.])
+  fi
   if test x"$set_asm" = x"arm"; then
     AC_MSG_ERROR([ARM assembly optimization is experimental. Use --enable-experimental to allow.])
   fi
@@ -673,6 +686,7 @@ AM_CONDITIONAL([ENABLE_MODULE_WHITELIST], [test x"$enable_module_whitelist" = x"
 AM_CONDITIONAL([ENABLE_MODULE_EXTRAKEYS], [test x"$enable_module_extrakeys" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_SCHNORRSIG], [test x"$enable_module_schnorrsig" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_ECDSA_S2C], [test x"$enable_module_ecdsa_s2c" = x"yes"])
+AM_CONDITIONAL([ENABLE_MODULE_ECDSA_ADAPTOR], [test x"$enable_module_ecdsa_adaptor" = x"yes"])
 AM_CONDITIONAL([USE_EXTERNAL_ASM], [test x"$use_external_asm" = x"yes"])
 AM_CONDITIONAL([USE_ASM_ARM], [test x"$set_asm" = x"arm"])
 AM_CONDITIONAL([ENABLE_MODULE_SURJECTIONPROOF], [test x"$enable_module_surjectionproof" = x"yes"])
@@ -698,6 +712,7 @@ echo "  module recovery         = $enable_module_recovery"
 echo "  module extrakeys        = $enable_module_extrakeys"
 echo "  module schnorrsig       = $enable_module_schnorrsig"
 echo "  module ecdsa-s2c        = $enable_module_ecdsa_s2c"
+echo "  module ecdsa-adaptor    = $enable_module_ecdsa_adaptor"
 echo
 echo "  asm                     = $set_asm"
 echo "  bignum                  = $set_bignum"

include/secp256k1_ecdsa_adaptor.h

@@ -0,0 +1,19 @@
+#ifndef SECP256K1_ECDSA_ADAPTOR_H
+#define SECP256K1_ECDSA_ADAPTOR_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** This module implements single signer ECDSA adaptor signatures following
+ *  "One-Time Verifiably Encrypted Signatures A.K.A. Adaptor Signatures" by
+ *  Lloyd Fournier
+ *  (https://lists.linuxfoundation.org/pipermail/lightning-dev/2019-November/002316.html
+ *  and https://github.com/LLFourn/one-time-VES/blob/master/main.pdf).
+*/
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SECP256K1_ECDSA_ADAPTOR_H */

src/modules/ecdsa_adaptor/Makefile.am.include

@@ -0,0 +1 @@
+include_HEADERS += include/secp256k1_ecdsa_adaptor.h

src/modules/ecdsa_adaptor/main_impl.h

@@ -0,0 +1,12 @@
+/**********************************************************************
+ * Copyright (c) 2020-2021 Jonas Nick, Jesse Posner                   *
+ * Distributed under the MIT software license, see the accompanying   *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef SECP256K1_MODULE_ECDSA_ADAPTOR_MAIN_H
+#define SECP256K1_MODULE_ECDSA_ADAPTOR_MAIN_H
+
+#include "include/secp256k1_ecdsa_adaptor.h"
+
+#endif

src/secp256k1.c

@@ -831,6 +831,10 @@ int secp256k1_ec_pubkey_combine(const secp256k1_context* ctx, secp256k1_pubkey *
 # include "modules/ecdsa_s2c/main_impl.h"
 #endif
 
+#ifdef ENABLE_MODULE_ECDSA_ADAPTOR
+# include "modules/ecdsa_adaptor/main_impl.h"
+#endif
+
 #ifdef ENABLE_MODULE_MUSIG
 # include "modules/musig/main_impl.h"
 #endif