From 349b37273ee1337f9b0b3d622c0e27932580cfdd Mon Sep 17 00:00:00 2001 From: Gilles Peskine Date: Sat, 3 Apr 2021 21:40:11 +0200 Subject: [PATCH] Fix an incorrect comment about fix_negative We're subtracting multiples of 2^bits, not 2^(bits+32). Signed-off-by: Gilles Peskine --- library/ecp_curves.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/library/ecp_curves.c b/library/ecp_curves.c index b167443cf8..bf84effb69 100644 --- a/library/ecp_curves.c +++ b/library/ecp_curves.c @@ -1034,7 +1034,7 @@ static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry ) /* * If the result is negative, we get it in the form - * c * 2^(bits + 32) + N, with c negative and N positive shorter than 'bits' + * c * 2^bits + N, with c negative and N positive shorter than 'bits' */ MBEDTLS_STATIC_TESTABLE void mbedtls_ecp_fix_negative( mbedtls_mpi *N, signed char c, size_t bits ) @@ -1049,8 +1049,8 @@ void mbedtls_ecp_fix_negative( mbedtls_mpi *N, signed char c, size_t bits ) } N->s = -1; - /* Add |c| * 2^(bits + 32) to the absolute value. Since c and N are - * negative, this adds c * 2^(bits + 32). */ + /* Add |c| * 2^bits to the absolute value. Since c and N are + * negative, this adds c * 2^bits. */ mbedtls_mpi_uint msw = (mbedtls_mpi_uint) -c; #if defined(MBEDTLS_HAVE_INT64) if( bits == 224 )