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Remove another local MPI from ecp_normalize_jac_many()

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Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit is contained in:
Hanno Becker
2022-01-04 06:32:11 +00:00
parent 02a999b91a
commit b8442cd9c6
1 changed files with 26 additions and 19 deletions
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45
library/ecp.c
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@ -1279,7 +1279,7 @@ static int ecp_normalize_jac_many( const mbedtls_ecp_group *grp,
#else #else
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
size_t i; size_t i;
mbedtls_mpi *c, u, Zi; mbedtls_mpi *c, t;
if( ( c = mbedtls_calloc( T_size, sizeof( mbedtls_mpi ) ) ) == NULL ) if( ( c = mbedtls_calloc( T_size, sizeof( mbedtls_mpi ) ) ) == NULL )
return( MBEDTLS_ERR_ECP_ALLOC_FAILED ); return( MBEDTLS_ERR_ECP_ALLOC_FAILED );
@ -1287,7 +1287,7 @@ static int ecp_normalize_jac_many( const mbedtls_ecp_group *grp,
for( i = 0; i < T_size; i++ ) for( i = 0; i < T_size; i++ )
mbedtls_mpi_init( &c[i] ); mbedtls_mpi_init( &c[i] );
mbedtls_mpi_init( &u ); mbedtls_mpi_init( &Zi ); mbedtls_mpi_init( &t );
/* /*
* c[i] = Z_0 * ... * Z_i * c[i] = Z_0 * ... * Z_i
@ -1299,33 +1299,40 @@ static int ecp_normalize_jac_many( const mbedtls_ecp_group *grp,
} }
/* /*
* u = 1 / (Z_0 * ... * Z_n) mod P * c[n] = 1 / (Z_0 * ... * Z_n) mod P
*/ */
MPI_ECP_INV( &u, &c[T_size-1] ); MPI_ECP_INV( &c[T_size-1], &c[T_size-1] );
for( i = T_size - 1; ; i-- ) for( i = T_size - 1; ; i-- )
{ {
/* /* At the start of iteration i (note that i decrements), we have
* Zi = 1 / Z_i mod p * - c[j] = Z_0 * .... * Z_j for j < i,
* u = 1 / (Z_0 * ... * Z_i) mod P * - c[j] = 1 / (Z_0 * .... * Z_j) for j == i,
*
* This is maintained via
* - c[i-1] <- c[i] * Z_i
*
* We also derive 1/Z_i = c[i] * c[i-1] for i>0 and use that
* to do the actual normalization. For i==0, we already have
* c[0] = 1 / Z_0.
*/ */
if( i == 0 )
if( i > 0 )
{ {
MPI_ECP_MOV( &Zi, &u ); /* Compute 1/Z_i and establish invariant for the next iteration. */
MPI_ECP_MUL( &t, &c[i], &c[i-1] );
MPI_ECP_MUL( &c[i-1], &c[i], &T[i]->Z );
} }
else else
{ {
MPI_ECP_MUL( &Zi, &u, &c[i-1] ); MPI_ECP_MOV( &t, &c[0] );
MPI_ECP_MUL( &u, &u, &T[i]->Z );
} }
/* /* Now t holds 1 / Z_i; normalize as in ecp_normalize_jac() */
* proceed as in normalize() MPI_ECP_MUL( &T[i]->Y, &T[i]->Y, &t );
*/ MPI_ECP_MUL( &t, &t, &t );
MPI_ECP_MUL( &T[i]->Y, &T[i]->Y, &Zi ); MPI_ECP_MUL( &T[i]->X, &T[i]->X, &t );
MPI_ECP_MUL( &Zi, &Zi, &Zi ); MPI_ECP_MUL( &T[i]->Y, &T[i]->Y, &t );
MPI_ECP_MUL( &T[i]->X, &T[i]->X, &Zi );
MPI_ECP_MUL( &T[i]->Y, &T[i]->Y, &Zi );
/* /*
* Post-precessing: reclaim some memory by shrinking coordinates * Post-precessing: reclaim some memory by shrinking coordinates
@ -1343,7 +1350,7 @@ static int ecp_normalize_jac_many( const mbedtls_ecp_group *grp,
cleanup: cleanup:
mbedtls_mpi_free( &u ); mbedtls_mpi_free( &Zi ); mbedtls_mpi_free( &t );
for( i = 0; i < T_size; i++ ) for( i = 0; i < T_size; i++ )
mbedtls_mpi_free( &c[i] ); mbedtls_mpi_free( &c[i] );
mbedtls_free( c ); mbedtls_free( c );