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Merge pull request #3209 from aurel32/fix-ecp_double_add_mxz

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Fix wrong modulo call in ecp_double_add_mxz
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Manuel Pégourié-Gonnard 2020-04-24 09:28:17 +02:00 committed by GitHub
commit b1c8e41ae3
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2 changed files with 5 additions and 1 deletions
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ChangeLog.d/fix-ecp_double_add_mxz.txt Normal file
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@ -0,0 +1,4 @@
Changes
* Fix minor performance issue in operations on Curve25519 caused by using a
suboptimal modular reduction in one place. Found and fix contributed by
Aurelien Jarno in #3209.

2
library/ecp.c
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@ -2332,7 +2332,7 @@ static int ecp_double_add_mxz( const mbedtls_ecp_group *grp,
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, &D, &Q->X, &Q->Z ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &DA, &D, &A ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &CB, &C, &B ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &S->X, &DA, &CB ) ); MOD_MUL( S->X );
MBEDTLS_MPI_CHK( mbedtls_mpi_add_mod( grp, &S->X, &DA, &CB ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &S->X, &S->X, &S->X ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, &S->Z, &DA, &CB ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &S->Z, &S->Z, &S->Z ) );