Safegcd inverses, drop Jacobi symbols, remove libgmp

.cirrus.yml

@@ -1,6 +1,5 @@
 env:
   WIDEMUL: auto
-  BIGNUM: auto
   STATICPRECOMPUTATION: yes
   ECMULTGENPRECISION: auto
   ASM: no
@@ -59,17 +58,15 @@ task:
     - env: {WIDEMUL: int128,  RECOVERY: yes,            EXPERIMENTAL: yes, SCHNORRSIG: yes}
     - env: {WIDEMUL: int128,                 ECDH: yes, EXPERIMENTAL: yes, SCHNORRSIG: yes}
     - env: {WIDEMUL: int128,  ASM: x86_64}
-    - env: {BIGNUM: no}
-    - env: {BIGNUM: no,       RECOVERY: yes,            EXPERIMENTAL: yes, SCHNORRSIG: yes}
-    - env: {BIGNUM: no,       STATICPRECOMPUTATION: no}
+    - env: {                  RECOVERY: yes,            EXPERIMENTAL: yes, SCHNORRSIG: yes}
+    - env: {                  STATICPRECOMPUTATION: no}
     - env: {BUILD: distcheck, WITH_VALGRIND: no, CTIMETEST: no, BENCH: no}
     - env: {CPPFLAGS: -DDETERMINISTIC}
     - env: {CFLAGS: -O0, CTIMETEST: no}
     - env:
         CFLAGS:  "-fsanitize=undefined -fno-omit-frame-pointer"
         LDFLAGS: "-fsanitize=undefined -fno-omit-frame-pointer"
         UBSAN_OPTIONS: "print_stacktrace=1:halt_on_error=1"
-        BIGNUM: no
         ASM: x86_64
         ECDH: yes
         RECOVERY: yes
@@ -80,7 +77,6 @@ task:
     - env: { ECMULTGENPRECISION: 8 }
     - env:
         RUN_VALGRIND: yes
-        BIGNUM: no
         ASM: x86_64
         ECDH: yes
         RECOVERY: yes
@@ -115,12 +111,6 @@ task:
         CC: i686-linux-gnu-gcc
     - env:
         CC: clang --target=i686-pc-linux-gnu -isystem /usr/i686-linux-gnu/include
-  matrix:
-    - env:
-        BIGNUM: gmp
-    - env:
-        BIGNUM: no
-  << : *MERGE_BASE
   test_script:
     - ./ci/cirrus.sh
   << : *CAT_LOGS
@@ -178,7 +168,7 @@ task:
     # If we haven't restored from cached (and just run brew install), this is a no-op.
     - brew link valgrind
   brew_script:
-    - brew install automake libtool gmp gcc@9
+    - brew install automake libtool gcc@9
   << : *MERGE_BASE
   test_script:
     - ./ci/cirrus.sh
@@ -195,7 +185,6 @@ task:
     HOST: s390x-linux-gnu
     BUILD:
     WITH_VALGRIND: no
-    BIGNUM: no
     ECDH: yes
     RECOVERY: yes
     EXPERIMENTAL: yes

Makefile.am

@@ -14,8 +14,6 @@ noinst_HEADERS += src/scalar_8x32_impl.h
 noinst_HEADERS += src/scalar_low_impl.h
 noinst_HEADERS += src/group.h
 noinst_HEADERS += src/group_impl.h
-noinst_HEADERS += src/num_gmp.h
-noinst_HEADERS += src/num_gmp_impl.h
 noinst_HEADERS += src/ecdsa.h
 noinst_HEADERS += src/ecdsa_impl.h
 noinst_HEADERS += src/eckey.h
@@ -26,14 +24,16 @@ noinst_HEADERS += src/ecmult_const.h
 noinst_HEADERS += src/ecmult_const_impl.h
 noinst_HEADERS += src/ecmult_gen.h
 noinst_HEADERS += src/ecmult_gen_impl.h
-noinst_HEADERS += src/num.h
-noinst_HEADERS += src/num_impl.h
 noinst_HEADERS += src/field_10x26.h
 noinst_HEADERS += src/field_10x26_impl.h
 noinst_HEADERS += src/field_5x52.h
 noinst_HEADERS += src/field_5x52_impl.h
 noinst_HEADERS += src/field_5x52_int128_impl.h
 noinst_HEADERS += src/field_5x52_asm_impl.h
+noinst_HEADERS += src/modinv32.h
+noinst_HEADERS += src/modinv32_impl.h
+noinst_HEADERS += src/modinv64.h
+noinst_HEADERS += src/modinv64_impl.h
 noinst_HEADERS += src/assumptions.h
 noinst_HEADERS += src/util.h
 noinst_HEADERS += src/scratch.h

README.md

@@ -34,11 +34,11 @@ Implementation details
   * Optimized implementation of arithmetic modulo the curve's field size (2^256 - 0x1000003D1).
     * Using 5 52-bit limbs (including hand-optimized assembly for x86_64, by Diederik Huys).
     * Using 10 26-bit limbs (including hand-optimized assembly for 32-bit ARM, by Wladimir J. van der Laan).
-  * Field inverses and square roots using a sliding window over blocks of 1s (by Peter Dettman).
 * Scalar operations
   * Optimized implementation without data-dependent branches of arithmetic modulo the curve's order.
     * Using 4 64-bit limbs (relying on __int128 support in the compiler).
     * Using 8 32-bit limbs.
+* Modular inverses (both field elements and scalars) based on [safegcd](https://gcd.cr.yp.to/index.html) with some modifications, and a variable-time variant (by Peter Dettman).
 * Group operations
   * Point addition formula specifically simplified for the curve equation (y^2 = x^3 + 7).
   * Use addition between points in Jacobian and affine coordinates where possible.

build-aux/m4/bitcoin_secp.m4

@@ -75,19 +75,6 @@ if test x"$has_libcrypto" = x"yes" && test x"$has_openssl_ec" = x; then
 fi
 ])
 
-dnl
-AC_DEFUN([SECP_GMP_CHECK],[
-if test x"$has_gmp" != x"yes"; then
-  CPPFLAGS_TEMP="$CPPFLAGS"
-  CPPFLAGS="$GMP_CPPFLAGS $CPPFLAGS"
-  LIBS_TEMP="$LIBS"
-  LIBS="$GMP_LIBS $LIBS"
-  AC_CHECK_HEADER(gmp.h,[AC_CHECK_LIB(gmp, __gmpz_init,[has_gmp=yes; GMP_LIBS="$GMP_LIBS -lgmp"; AC_DEFINE(HAVE_LIBGMP,1,[Define this symbol if libgmp is installed])])])
-  CPPFLAGS="$CPPFLAGS_TEMP"
-  LIBS="$LIBS_TEMP"
-fi
-])
-
 AC_DEFUN([SECP_VALGRIND_CHECK],[
 if test x"$has_valgrind" != x"yes"; then
   CPPFLAGS_TEMP="$CPPFLAGS"

ci/cirrus.sh

@@ -14,7 +14,7 @@ valgrind --version || true
 
 ./configure \
     --enable-experimental="$EXPERIMENTAL" \
-    --with-test-override-wide-multiply="$WIDEMUL" --with-bignum="$BIGNUM" --with-asm="$ASM" \
+    --with-test-override-wide-multiply="$WIDEMUL" --with-asm="$ASM" \
     --enable-ecmult-static-precomputation="$STATICPRECOMPUTATION" --with-ecmult-gen-precision="$ECMULTGENPRECISION" \
     --enable-module-ecdh="$ECDH" --enable-module-recovery="$RECOVERY" \
     --enable-module-schnorrsig="$SCHNORRSIG" \

ci/linux-debian.Dockerfile

@@ -8,6 +8,6 @@ RUN apt-get update
 RUN apt-get install --no-install-recommends --no-upgrade -y \
         git ca-certificates \
         make automake libtool pkg-config dpkg-dev valgrind qemu-user \
-        gcc clang libc6-dbg libgmp-dev \
-        gcc-i686-linux-gnu libc6-dev-i386-cross libc6-dbg:i386 libgmp-dev:i386 \
+        gcc clang libc6-dbg \
+        gcc-i686-linux-gnu libc6-dev-i386-cross libc6-dbg:i386 \
         gcc-s390x-linux-gnu libc6-dev-s390x-cross libc6-dbg:s390x

configure.ac

@@ -48,17 +48,12 @@ case $host_os in
          # in expected paths because they may conflict with system files. Ask
          # Homebrew where each one is located, then adjust paths accordingly.
          openssl_prefix=`$BREW --prefix openssl 2>/dev/null`
-         gmp_prefix=`$BREW --prefix gmp 2>/dev/null`
          valgrind_prefix=`$BREW --prefix valgrind 2>/dev/null`
          if test x$openssl_prefix != x; then
            PKG_CONFIG_PATH="$openssl_prefix/lib/pkgconfig:$PKG_CONFIG_PATH"
            export PKG_CONFIG_PATH
            CRYPTO_CPPFLAGS="-I$openssl_prefix/include"
          fi
-         if test x$gmp_prefix != x; then
-           GMP_CPPFLAGS="-I$gmp_prefix/include"
-           GMP_LIBS="-L$gmp_prefix/lib"
-         fi
          if test x$valgrind_prefix != x; then
            VALGRIND_CPPFLAGS="-I$valgrind_prefix/include"
          fi
@@ -164,9 +159,6 @@ AC_ARG_ENABLE(external_default_callbacks,
 # Legal values are int64 (for [u]int64_t), int128 (for [unsigned] __int128), and auto (the default).
 AC_ARG_WITH([test-override-wide-multiply], [] ,[set_widemul=$withval], [set_widemul=auto])
 
-AC_ARG_WITH([bignum], [AS_HELP_STRING([--with-bignum=gmp|no|auto],
-[bignum implementation to use [default=auto]])],[req_bignum=$withval], [req_bignum=auto])
-
 AC_ARG_WITH([asm], [AS_HELP_STRING([--with-asm=x86_64|arm|no|auto],
 [assembly optimizations to use (experimental: arm) [default=auto]])],[req_asm=$withval], [req_asm=auto])
 
@@ -245,32 +237,6 @@ else
   esac
 fi
 
-if test x"$req_bignum" = x"auto"; then
-  SECP_GMP_CHECK
-  if test x"$has_gmp" = x"yes"; then
-    set_bignum=gmp
-  fi
-
-  if test x"$set_bignum" = x; then
-    set_bignum=no
-  fi
-else
-  set_bignum=$req_bignum
-  case $set_bignum in
-  gmp)
-    SECP_GMP_CHECK
-    if test x"$has_gmp" != x"yes"; then
-      AC_MSG_ERROR([gmp bignum explicitly requested but libgmp not available])
-    fi
-    ;;
-  no)
-    ;;
-  *)
-    AC_MSG_ERROR([invalid bignum implementation selection])
-    ;;
-  esac
-fi
-
 # Select assembly optimization
 use_external_asm=no
 
@@ -308,24 +274,6 @@ auto)
   ;;
 esac
 
-# Select bignum implementation
-case $set_bignum in
-gmp)
-  AC_DEFINE(HAVE_LIBGMP, 1, [Define this symbol if libgmp is installed])
-  AC_DEFINE(USE_NUM_GMP, 1, [Define this symbol to use the gmp implementation for num])
-  AC_DEFINE(USE_FIELD_INV_NUM, 1, [Define this symbol to use the num-based field inverse implementation])
-  AC_DEFINE(USE_SCALAR_INV_NUM, 1, [Define this symbol to use the num-based scalar inverse implementation])
-  ;;
-no)
-  AC_DEFINE(USE_NUM_NONE, 1, [Define this symbol to use no num implementation])
-  AC_DEFINE(USE_FIELD_INV_BUILTIN, 1, [Define this symbol to use the native field inverse implementation])
-  AC_DEFINE(USE_SCALAR_INV_BUILTIN, 1, [Define this symbol to use the native scalar inverse implementation])
-  ;;
-*)
-  AC_MSG_ERROR([invalid bignum implementation])
-  ;;
-esac
-
 # Set ecmult window size
 if test x"$req_ecmult_window" = x"auto"; then
   set_ecmult_window=15
@@ -390,11 +338,6 @@ else
   enable_openssl_tests=no
 fi
 
-if test x"$set_bignum" = x"gmp"; then
-  SECP_LIBS="$SECP_LIBS $GMP_LIBS"
-  SECP_INCLUDES="$SECP_INCLUDES $GMP_CPPFLAGS"
-fi
-
 if test x"$enable_valgrind" = x"yes"; then
   SECP_INCLUDES="$SECP_INCLUDES $VALGRIND_CPPFLAGS"
 fi
@@ -571,7 +514,6 @@ echo "  module extrakeys        = $enable_module_extrakeys"
 echo "  module schnorrsig       = $enable_module_schnorrsig"
 echo
 echo "  asm                     = $set_asm"
-echo "  bignum                  = $set_bignum"
 echo "  ecmult window size      = $set_ecmult_window"
 echo "  ecmult gen prec. bits   = $set_ecmult_gen_precision"
 # Hide test-only options unless they're used.