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Reduce the size of mbedtls_mpi

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Reduce the size of mbedtls_mpi from 3 words to 2 on most architectures.

This also reduces the code size significantly in bignum.o and ecp_curves.o,
with negligible variations in other modules.

This removes the ability to set MBEDTLS_MPI_MAX_LIMBS to a value >=65536,
but we don't support customizing this value anyway (it's always 10000).

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2023-06-29 19:26:48 +02:00
parent 92a55bf5ea
commit 053022fe24
3 changed files with 16 additions and 8 deletions
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7
include/mbedtls/bignum.h
View file

@ -214,10 +214,13 @@ typedef struct mbedtls_mpi {
* Note that this implies that calloc() or `... = {0}` does not create
* a valid MPI representation. You must call mbedtls_mpi_init().
*/
int MBEDTLS_PRIVATE(s);
signed short MBEDTLS_PRIVATE(s);
/** Total number of limbs in \c p. */
size_t MBEDTLS_PRIVATE(n);
unsigned short MBEDTLS_PRIVATE(n);
#if MBEDTLS_MPI_MAX_LIMBS > 65535
#error "MBEDTLS_MPI_MAX_LIMBS > 65535 is not supported"
#endif
/** Pointer to limbs.
*

12
library/bignum.c
View file

@ -114,7 +114,9 @@ int mbedtls_mpi_grow(mbedtls_mpi *X, size_t nblimbs)
mbedtls_free(X->p);
}
X->n = nblimbs;
/* nblimbs fits in n because we ensure that MBEDTLS_MPI_MAX_LIMBS
* fits, and we've checked that nblimbs <= MBEDTLS_MPI_MAX_LIMBS. */
X->n = (unsigned short) nblimbs;
X->p = p;
}
@ -162,7 +164,9 @@ int mbedtls_mpi_shrink(mbedtls_mpi *X, size_t nblimbs)
mbedtls_free(X->p);
}
X->n = i;
/* i fits in n because we ensure that MBEDTLS_MPI_MAX_LIMBS
* fits, and we've checked that i <= nblimbs <= MBEDTLS_MPI_MAX_LIMBS. */
X->n = (unsigned short) i;
X->p = p;
return 0;
@ -1574,8 +1578,8 @@ static void mpi_montred(mbedtls_mpi *A, const mbedtls_mpi *N,
{
mbedtls_mpi_uint z = 1;
mbedtls_mpi U;
U.n = U.s = (int) z;
U.n = 1;
U.s = 1;
U.p = &z;
mpi_montmul(A, &U, N, mm, T);

5
library/ecp_curves.c
View file

@ -4512,12 +4512,13 @@ static const mbedtls_ecp_point brainpoolP512r1_T[32] = {
defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
/*
* Create an MPI from embedded constants
* (assumes len is an exact multiple of sizeof(mbedtls_mpi_uint))
* (assumes len is an exact multiple of sizeof(mbedtls_mpi_uint) and
* len < 1048576)
*/
static inline void ecp_mpi_load(mbedtls_mpi *X, const mbedtls_mpi_uint *p, size_t len)
{
X->s = 1;
X->n = len / sizeof(mbedtls_mpi_uint);
X->n = (unsigned short) (len / sizeof(mbedtls_mpi_uint));
X->p = (mbedtls_mpi_uint *) p;
}
#endif