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Make WINDOW_G configurable 

This makes WINDOW_G a configurable value in the range of [2..24].
The upper limit of 24 is a defensive choice. The code is probably
correct for values up to 27 but those larger values yield in huge
tables (>= 256MiB), which are i) unlikely to be really beneficial
in practice and ii) increasingly difficult to test.
This commit is contained in:
Tim Ruffing 2019-03-06 13:12:33 +01:00
parent 1a02d6ce51
commit 2842dc523e
3 changed files with 70 additions and 13 deletions
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32
configure.ac
View File

@ -151,6 +151,15 @@ AC_ARG_WITH([scalar], [AS_HELP_STRING([--with-scalar=64bit|32bit|auto],
AC_ARG_WITH([asm], [AS_HELP_STRING([--with-asm=x86_64|arm|no|auto]
[Specify assembly optimizations to use. Default is auto (experimental: arm)])],[req_asm=$withval], [req_asm=auto])
AC_ARG_WITH([ecmult-window], [AS_HELP_STRING([--with-ecmult-window=SIZE|auto],
[window size for ecmult precomputation for verification, specified as integer in range [2..24].]
[Larger values result in possibly better performance at the cost of an exponentially larger precomputed table.]
[The table will store 2^(SIZE-2) * 64 bytes of data but can be larger in memory due to platform-specific padding and alignment.]
[If the endomorphism optimization is enabled, two tables of this size are used instead of only one.]
["auto" is a reasonable setting for desktop machines (currently 15). [default=auto]]
)],
[req_ecmult_window=$withval], [req_ecmult_window=auto])
AC_CHECK_TYPES([__int128])
if test x"$enable_coverage" = x"yes"; then
@ -387,6 +396,28 @@ case $set_scalar in
;;
esac
#set ecmult window size
if test x"$req_ecmult_window" = x"auto"; then
set_ecmult_window=15
else
set_ecmult_window=$req_ecmult_window
fi
error_window_size=['window size for ecmult precomputation not an integer in range [2..24] or "auto"']
case $set_ecmult_window in
''|*[[!0-9]]*)
# no valid integer
AC_MSG_ERROR($error_window_size)
;;
*)
if test "$set_ecmult_window" -lt 2 -o "$set_ecmult_window" -gt 24 ; then
# not in range
AC_MSG_ERROR($error_window_size)
fi
AC_DEFINE_UNQUOTED(ECMULT_WINDOW_SIZE, $set_ecmult_window, [Set window size for ecmult precomputation])
;;
esac
if test x"$use_tests" = x"yes"; then
SECP_OPENSSL_CHECK
if test x"$has_openssl_ec" = x"yes"; then
@ -516,6 +547,7 @@ echo " asm = $set_asm"
echo " bignum = $set_bignum"
echo " field = $set_field"
echo " scalar = $set_scalar"
echo " ecmult window size = $set_ecmult_window"
echo
echo " CC = $CC"
echo " CFLAGS = $CFLAGS"

1
src/basic-config.h
View File

@ -28,6 +28,7 @@
#define USE_SCALAR_INV_BUILTIN 1
#define USE_FIELD_10X26 1
#define USE_SCALAR_8X32 1
#define ECMULT_WINDOW_SIZE 15
#endif /* USE_BASIC_CONFIG */

50
src/ecmult_impl.h
View File

@ -30,16 +30,32 @@
# endif
#else
/* optimal for 128-bit and 256-bit exponents. */
#define WINDOW_A 5
/** larger numbers may result in slightly better performance, at the cost of
exponentially larger precomputed tables. */
#ifdef USE_ENDOMORPHISM
/** Two tables for window size 15: 1.375 MiB. */
#define WINDOW_G 15
#else
/** One table for window size 16: 1.375 MiB. */
#define WINDOW_G 16
# define WINDOW_A 5
/** Larger values for ECMULT_WINDOW_SIZE result in possibly better
* performance at the cost of an exponentially larger precomputed
* table. The exact table size is
* (1 << (WINDOW_G - 2)) * sizeof(secp256k1_ge_storage) bytes,
* where sizeof(secp256k1_ge_storage) is typically 64 bytes but can
* be larger due to platform-specific padding and alignment.
* If the endomorphism optimization is enabled (USE_ENDOMORMPHSIM)
* two tables of this size are used instead of only one.
*/
# define WINDOW_G ECMULT_WINDOW_SIZE
#endif
/* Noone will ever need more than a window size of 24. The code might
* be correct for larger values of ECMULT_WINDOW_SIZE but this is not
* not tested.
*
* The following limitations are known, and there are probably more:
* If WINDOW_G > 27 and size_t has 32 bits, then the code is incorrect
* because the size of the memory object that we allocate (in bytes)
* will not fit in a size_t.
* If WINDOW_G > 31 and int has 32 bits, then the code is incorrect
* because certain expressions will overflow.
*/
#if ECMULT_WINDOW_SIZE < 2 || ECMULT_WINDOW_SIZE > 24
# error Set ECMULT_WINDOW_SIZE to an integer in range [2..24].
#endif
#ifdef USE_ENDOMORPHISM
@ -311,7 +327,12 @@ static void secp256k1_ecmult_context_build(secp256k1_ecmult_context *ctx, const
/* get the generator */
secp256k1_gej_set_ge(&gj, &secp256k1_ge_const_g);
ctx->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, sizeof((*ctx->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G));
{
size_t size = sizeof((*ctx->pre_g)[0]) * ((size_t)ECMULT_TABLE_SIZE(WINDOW_G));
/* check for overflow */
VERIFY_CHECK(size / sizeof((*ctx->pre_g)[0]) == ((size_t)ECMULT_TABLE_SIZE(WINDOW_G)));
ctx->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);
}
/* precompute the tables with odd multiples */
secp256k1_ecmult_odd_multiples_table_storage_var(ECMULT_TABLE_SIZE(WINDOW_G), *ctx->pre_g, &gj);
@ -321,7 +342,10 @@ static void secp256k1_ecmult_context_build(secp256k1_ecmult_context *ctx, const
secp256k1_gej g_128j;
int i;
ctx->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, sizeof((*ctx->pre_g_128)[0]) * ECMULT_TABLE_SIZE(WINDOW_G));
size_t size = sizeof((*ctx->pre_g_128)[0]) * ((size_t) ECMULT_TABLE_SIZE(WINDOW_G));
/* check for overflow */
VERIFY_CHECK(size / sizeof((*ctx->pre_g_128)[0]) == ((size_t)ECMULT_TABLE_SIZE(WINDOW_G)));
ctx->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);
/* calculate 2^128*generator */
g_128j = gj;
@ -338,7 +362,7 @@ static void secp256k1_ecmult_context_clone(secp256k1_ecmult_context *dst,
if (src->pre_g == NULL) {
dst->pre_g = NULL;
} else {
size_t size = sizeof((*dst->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G);
size_t size = sizeof((*dst->pre_g)[0]) * ((size_t)ECMULT_TABLE_SIZE(WINDOW_G));
dst->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);
memcpy(dst->pre_g, src->pre_g, size);
}
@ -346,7 +370,7 @@ static void secp256k1_ecmult_context_clone(secp256k1_ecmult_context *dst,
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);
size_t size = sizeof((*dst->pre_g_128)[0]) * ((size_t)ECMULT_TABLE_SIZE(WINDOW_G));
dst->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);
memcpy(dst->pre_g_128, src->pre_g_128, size);
}