From dc406b82b20481bde74a60fa8a776285d3fb9cf3 Mon Sep 17 00:00:00 2001 From: Mahavir Jain Date: Thu, 18 Nov 2021 15:39:30 +0530 Subject: [PATCH] bignum: add provision for combined software and hardware MPI approach For exponential mod (API mbedtls_mpi_exp_mod) operation, some ESP target chips needs to have ability for both hardware and software implementation. Hardware implementation provided performance advantage but it can only support upto 3072 bit operations (e.g., ESP32-C3) and hence we fallback to software implementation in such cases (e.g., 4096 bit operations). Earlier this was handled using linker "--wrap" flag but that does not work in all scenarios as API `mbedtls_mpi_exp_mod` is being used in same tranlation (compilation unit). This approach was found to be next best option with minimal changes in mbedTLS library. --- library/bignum.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/library/bignum.c b/library/bignum.c index 33bab5fced..c8d21db72c 100644 --- a/library/bignum.c +++ b/library/bignum.c @@ -2197,9 +2197,15 @@ cleanup: /* * Sliding-window exponentiation: X = A^E mod N (HAC 14.85) */ +#if !defined(MBEDTLS_MPI_EXP_MOD_ALT_FALLBACK) int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi *E, const mbedtls_mpi *N, mbedtls_mpi *prec_RR ) +#else +int mbedtls_mpi_exp_mod_soft( mbedtls_mpi *X, const mbedtls_mpi *A, + const mbedtls_mpi *E, const mbedtls_mpi *N, + mbedtls_mpi *prec_RR ) +#endif { int ret; size_t wbits, wsize, one = 1;