core: LTC mpi_desc.c: update to mbedTLS 3.4.0 API

MbedTLS 3.4.0 normally doesn't permit access to the internal fields of
mbedtls_mpi. However, mpi_desc.c manipulates the internals of
mbedtls_mpi so define MBEDTLS_ALLOW_PRIVATE_ACCESS to allow accesses to
the internals of mbedtls_mpi.

mbedtls_mpi_is_prime() is replaced by mbedtls_mpi_is_prime_ext() so
switch to use that instead to implement isprime() in the internal LTC
mpi_desc interface.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-By: Jerome Forissier <jerome.forissier@linaro.org>

core/lib/libtomcrypt/mpi_desc.c

@@ -602,9 +602,9 @@ static int rng_read(void *ignored __unused, unsigned char *buf, size_t blen)
 	return 0;
 }
 
-static int isprime(void *a, int b __unused, int *c)
+static int isprime(void *a, int b, int *c)
 {
-	int res = mbedtls_mpi_is_prime(a, rng_read, NULL);
+	int res = mbedtls_mpi_is_prime_ext(a, b, rng_read, NULL);
 
 	if (res == MBEDTLS_ERR_MPI_ALLOC_FAILED)
 		return CRYPT_MEM;

core/lib/libtomcrypt/sub.mk

@@ -148,6 +148,7 @@ srcs-$(_CFG_CORE_LTC_X25519) += x25519.c
 srcs-$(_CFG_CORE_LTC_ED25519) += ed25519.c
 ifeq ($(_CFG_CORE_LTC_ACIPHER),y)
 srcs-y += mpi_desc.c
+cppflags-mpi_desc.c-y += -DMBEDTLS_ALLOW_PRIVATE_ACCESS
 endif
 
 srcs-y += tomcrypt.c