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Reduce number of temporary MPIs in ECP normalization

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Signed-off-by: Hanno Becker <hanno.becker@arm.com>
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Hanno Becker 2022-01-02 12:47:34 +00:00
parent 02b35bd00a
commit 76f897d699
1 changed files with 13 additions and 18 deletions
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31
library/ecp.c
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@ -1194,30 +1194,25 @@ static int ecp_normalize_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *p
return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
#else
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_mpi Zi, ZZi;
mbedtls_mpi_init( &Zi ); mbedtls_mpi_init( &ZZi );
mbedtls_mpi T;
mbedtls_mpi_init( &T );
/*
* X = X / Z^2 mod p
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &Zi, &pt->Z, &grp->P ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &ZZi, &Zi, &Zi ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &pt->X, &pt->X, &ZZi ) );
/* T <- 1 / Z */
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &T, &pt->Z, &grp->P ) );
/* Y' <- Y*T = Y / Z */
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &pt->Y, &pt->Y, &T ) );
/* T <- T^2 = 1 / Z^2 */
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T, &T, &T ) );
/* X <- X * T = X / Z^2 */
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &pt->X, &pt->X, &T ) );
/* Y'' <- Y' * T = Y / Z^3 */
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &pt->Y, &pt->Y, &T ) );
/*
* Y = Y / Z^3 mod p
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &pt->Y, &pt->Y, &ZZi ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &pt->Y, &pt->Y, &Zi ) );
/*
* Z = 1
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &pt->Z, 1 ) );
cleanup:
mbedtls_mpi_free( &Zi ); mbedtls_mpi_free( &ZZi );
mbedtls_mpi_free( &T );
return( ret );
#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT) */